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Biology
HSC Course
Stage 6
Communication
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Acknowledgments
This publication is copyright Learning Materials Production, Open Training and Education Network –
Distance Education, NSW Department of Education and Training, however it may contain material from
other sources which is not owned by Learning Materials Production. Learning Materials Production
would like to acknowledge the following people and organisations whose material has been used.
•
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. Amended
November 2002
All reasonable efforts have been made to obtain copyright permissions. All claims will be settled in
good faith.
Writer
Jane West and Steve Vassallo
Editor
Ric Morante
Illustrator
Thomas Brown
Photographs
Thomas Brown
David Stanley
Jane West
Layout
Gayle Reddy
Copyright in this material is reserved to the Crown in the right of the State of New South Wales.
Reproduction or transmittal in whole, or in part, other than in accordance with provisions of the
Copyright Act, is prohibited without the written authority of Learning Materials Production.
© Learning Materials Production, Open Training and Education Network – Distance Education,
NSW Department of Education and Training, 2003. 51 Wentworth Rd. Strathfield NSW 2135.
Contents
Module overview
Outcomes ............................................................................................ iii
Indicative time...................................................................................... iii
Resources............................................................................................ iii
Icons .....................................................................................................v
Glossary............................................................................................... vi
Part 1: Making sense of your surroundings.........................1–35
Part 2: Eye can see clearly .................................................1–29
Part 3: I can see the light ....................................................1–30
Part 4: Making sounds ........................................................1–24
Part 5: What’s this ear?.......................................................1–37
Part 6: It’s all in the head.....................................................1–34
Student evaluation of the module
Introduction
i
ii
Communication
Module overview
Humans are great communicators. Every waking hour of the day there is
a flood of information received by the senses. Some of these senses,
such as sight and hearing, play an important role in communication in
humans. Other organisms use sensory information that cannot be
detected by humans for communication. The brain plays an important
role in the interpretation of this information and controls behaviour.
Outcomes
This module increases students’ understanding of the history,
applications and uses of biology, implications of biology for society
and the environment and current issues, research and developments
in biology.
Indicative time
This module is divided into six parts. You need to spend at least five
hours on each part. Therefore, the module Communication is designed
so that you should take at least thirty indicative hours to complete.
Resources
Part 1:
Introduction
•
one single-edged razor blade or knife
•
scalpel
•
scissors
•
paper towel
iii
•
plastic garbage bags
•
rubber gloves.
Part 2:
•
hard clear plastic or glass
•
water
•
newspaper
•
two convex lenses
•
light source.
Part 6:
iv
•
microscope and prepared slides of neurones
•
a sheep’s brain from the butcher or abattoir
•
scalpel or knife
•
rubber gloves
•
newspaper
•
cutting board.
Communication
Icons
The following icons are used within this module. The meaning of each
icon is written beside it.
The hand icon means there is an activity for you to do.
It may be an experiment or you may make something.
You need to use a computer for this activity.
Discuss ideas with someone else. You could speak with
family or friends or anyone else who is available. Perhaps
you could telephone someone?
There is a safety issue that you need to consider.
There are suggested answers for the following questions
at the end of the part.
There is an exercise at the end of the part for you to
complete.
You need to go outside or away from your desk for this
activity.
Introduction
v
Glossary
The following words, listed here with their meanings, are found in the
learning material in this module. They appear bolded the first time they
occur in the learning material.
vi
accommodation
changing the focus in the eye by changing the
shape of the lens using the ciliary muscles
action potential
reversal of voltage across a nerve membrane
caused by the movement of sodium and
potassium ions
acuity
sharpness of vision
aqueous humour
transparent fluid that lies between the cornea
and the lens
axon
an extension on a neurone that takes the
impulse away from the cell body
binocular
involving the use of two eyes with overlapping
field of view resulting in depth perception
bioluminescence
the production of light by living organisms
blind spot
the place on the retina where the optic nerve
leaves the eye, contains no light sensitive cells
cataract
a clouding of the eye’s lens
cell body
part of the neurone that contains the nucleus
and other organelles
cetaceans
order of marine mammals
choroid
a layer between the sclera and the retina
ciliary body
contains the suspensory ligaments and the
ciliary muscles in the eye
cilary muscles
small muscles attached to the lens that change
the shape of the lens to focus on near and far
objects
colour blind
inability to detect particular colours caused by
a lack of specific colour cone cells
cone cell
light sensitive cell found on the retina of the
eye, particularly important in colour perception
conjunctiva
membrane lining the outer layer of the eye
cornea
transparent layer at the front of the eye,
refracts incoming light
Communication
Introduction
dendrite
extension of a neurone that transmits the signal
towards the cell body
effector
a muscle or gland that produces a response to a
stimulus
fovea
point on the retina with the greatest acuity and
the greatest number of cone cells
incus
one of three small bones in the middle ear
ion
a charged atom or group of atoms
iris
coloured part of the eye, controls the amount
of light entering the eye
labyrinth
organ in the inner ear that is responsible for
balance
lateral line
a visible line along the head and body of fish
and amphibians, senses low frequency sound
malleus
first of three small bones in the middle ear
mechanoreceptors
a receptor that responds to sound, pressure,
touch and position
monocular
vision from one eye
myelin sheath
a mixture of fat and proteins that acts as an
insulator around neurones
nerve
a bundle of neuronal fibres
neuromasts
sensory cells found in the lateral line organ of
fish and amphibians
neurone
a single nerve cell
neurotransmitters
chemicals that transmit the nerve impulse in
the synapse between two neurones
ocellus/ocelli
simple eye spot
ommatidia
visual units of the compound eye of
invertebrates
optic nerve
nerve that leaves the retina of the eye
otolith
calcareous mass found in the ear of some
vertebrates, important in sound perception in
fish
oval window
the connecting plate between the middle ear
and inner ear
peripheral
on the outer side
pheromones
chemicals released as a signal
vii
viii
photoreceptor
an organ or cell, sensitive to light
pitch
function of the frequency of a wave, high or
low sounds have high or low pitch
polarisation
separation of positive and negative ions
pupil
the opening in the iris of the eye
receptors
detect changes in the environment
recessive
not expressed in the phenotype unless it is the
only gene present
refraction
bending of light
refractory period
the time taken for a neurone to recover after
firing
resting potential
the normal state of a neurone, negatively
charged internally
retina
light sensitive lining on the back of the eye
rhodopsin
light sensitive pigment found in rod cells
rod cells
light sensitive cells especially useful for the
detection of low light
Schwann cells
a type of cell that produces the myelin sheath
around nerve cells
sclera
tough white coating in the eye
sex-linked
a gene found on one of the sex chromosomes
sound shadow
the acoustic shadow cast by the head, used in
the localisation of sound
spike
graphical interpretation of the firing of a
neurone
stapes
the third bone in the middle ear
stereocilia
hair-like extensions on hair cells that contact
the tectorial membrane and send an impulse to
the brain
stereoscopic
three dimensional view using the overlapping
field of view from two eyes
stimuli
an external message that excites a receptor
stimulus
singular of above
synapse
the gap between two neurones
syrinx
the voice box of birds
Communication
Introduction
threshold
a level of intensity necessary to fire a neurone
transparent
clear, see through
tympanic organ
a hearing organ found in insects that is similar
in structure to the mammalian eardrum
vitreous humour
jelly-like substance that fills the eye between
the lens and the retina
ix
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Biology
HSC Course
Stage 6
Communication
Part 1: Making sense of your surroundings
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Contents
Introduction ............................................................................... 2
The role of receptors ................................................................. 4
Detecting stimuli ...................................................................................4
Response to a stimulus........................................................................5
Senses in communication ......................................................... 7
Communication ....................................................................................7
Visual communication ............................................................. 12
Anatomy and function of the human eye .........................................12
Investigation of a mammalian eye ....................................................15
Detection of energy ................................................................. 20
Vision range........................................................................................22
Summary................................................................................. 25
Suggested answers................................................................. 27
Additional resources................................................................ 29
Exercises – Part 1 ................................................................... 31
Part 1: Making sense of your surroundings
1
Introduction
Spend a couple of minutes thinking about what you are sensing at the
moment. If you are reading this page your eyes are sending messages to
the brain based on the symbols it recognises on the page. What sounds
do you here? Do you feel hot or cold? What are your immediate smell
and/or taste sensations?
Humans and other animals are able to detect a range of stimuli (inputs)
from the environment. Which ones are useful for communication?
What senses are you using when you communicate to another human?
Is it the same as the senses used by other animals?
This part of the module identifies the range of senses involved in
communication. You will look at specific examples of communication in
humans and other animals.
You will be asked to dissect a mammalian eye during this part of the
module. To do this you will need to get an eye from your local butcher
or abattoir. As well as the eye you will need scissors, paper towels
and a single-edged razor blade, knife or scalpel. Alternative activities
are supplied.
In this Part you will be given opportunities to learn to:
•
identify the role of receptors in detecting stimuli
•
explain that the response to a stimulus involves:
•
2
–
stimulus
–
receptor
–
messenger
–
effector
–
response.
identify the limited range of wavelengths of the electromagnetic
spectrum detected by humans and compare this range with those of
other vertebrates and invertebrates
Communication
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•
describe the anatomy and function of the human eye, including the:
–
conjunctiva
–
cornea
–
sclera
–
choroid
–
retina
–
iris
–
lens
–
aqueous and vitreous humour
–
ciliary body
–
optic nerve.
In this Part you will be given opportunities to:
•
identify data sources, gather and process information from secondary
sources to identify the range of senses involved in communication
•
plan, choose equipment or resources and perform a first-hand
investigation of a mammalian eye to gather first-hand data to relate
structures to functions
•
use available evidence to suggest reasons for the differences in range
of electromagnetic radiation detected by humans and other animals.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Amended November 2002. The most up-to-date version can be
found on the Board’s website at:
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_listb.html
Part 1: Making sense of your surroundings
3
The role of receptors
Signals from the environment detected by our sense organs are called
stimuli (singular stimulus). These signals may be in the form of
vibrations, light and even changes in temperature. Organisms have
evolved special senses to detect stimuli and some of these senses are used
in communication. Animals use a range of different receptors to receive
messages involved in communication.
Detecting stimuli
Communication is a message requiring a sender and a receiver.
You observe the environment around you using your senses. Can you
remember all the senses that humans possess? See if you can list
them below.
_________________________________________________________
_________________________________________________________
You sense your environment through the use of your sense organs.
Now try to list as many sense organs as you can in the space below.
_________________________________________________________
_________________________________________________________
Check your answers
Our sense organs contain receptors that convert the stimulus from the
environment to a nerve impulse that goes to the brain. Receptors are
specialised cells. Their role is to detect stimuli. Each type of sense
organ contains a different kind of receptor.
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The receptor in the eye is called a photoreceptor because it
responds to light.
The sense of touch is actually made up of a number of different kinds of
receptors varying in size, shape, number and distribution within the skin.
They are responsible for relaying information about pressure,
temperature and pain.
The table below summarises the stimuli, receptors and organs found
in humans.
Sense organ
Receptor type
Stimulus
eye
photoreceptors
light (visible)
nose
chemoreceptors
chemicals
tongue
chemoreceptors
chemicals
skin
mechanoreceptors
pressure, touch
thermoreceptors
heat (infra-red)
ear
mechanoreceptors
hair cells
sound
semicircular canals
gravity
Some of these are more important than others for communication.
Response to a stimulus
Once a receptor detects a stimulus it sends a message along a nervous
pathway in the form of an electro chemical impulse. The nervous
pathway consists of a sensory neurone (a nerve cell often spelt neuron)
that sends the message to the connecting neurones in the central nervous
system (CNS) of the brain and spinal cord. From here it travels to the
motor neurone that transfers the message to effector organs such as
muscles or glands. You will learn more about this in Part 6 of
the module.
The impulse that travels through nerves is called the messenger. Once it
reaches the effector (in the muscle or in some cases a gland) the message
causes a reaction called a response.
Part 1: Making sense of your surroundings
5
The response to a stimulus can be demonstrated by the ‘knee jerk’ reflex
shown below.
Try this on a friend and/or have it done to you. Tap the knee gently in the
position shown in the diagram. You may have to try a few times until you
hit the right spot. The knee should jerk upwards in response.
The response to a stimulus can be summarized as follows:
stimulus
receptor
sensory neurone
messenger
motor neurone
effector
response
Do Exercise 1.1 now.
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Senses in communication
You have just learnt that a sensory receptor enables you to detect
stimuli and the mechanism whereby it causes a response. This section
will deal with how these actions are used in communication.
Remember communication occurs between a sender and a receiver.
Communication
Information communicated about the various parts of an organism’s
surroundings helps to construct a perception of its environment that
aids survival.
In biological terms communication means transferring or transmitting
a signal from one organism to another. This can be by means of sound,
visual signals, taste or smell, electrical impulse, touch or a
combination of these.
Living organisms are always communicating with each other whether it
is between members of different species or among members of the same
species. Communication is not limited to animals. Most flowering
plants communicate with animals to aid pollination and reproduction.
Animals use a range of senses to communicate a desire to mate with the
opposite sex, gather food and defend territory.
Range of senses used in communication
Humans have five senses, touch, taste, smell, sight and hearing.
Animals are not limited to only these senses. Each species relies on
different senses and has different depths of perception.
Part 1: Making sense of your surroundings
7
Examples of animal senses
Some examples of animal senses not shared by humans are:
•
echolocation
•
lateral line systems
•
Jacobsen’s organ
•
electric field detection.
Echolocation
Dolphins, whales and bats use this form of hearing to communicate and
to navigate. Dolphins produce 700 clicks per second and can locate
objects hundreds of metres away by this method. A bat flying silently
across the night sky is actually using sound to navigate but we are unable
to detect the sound.
Lateral line systems
Many fish have a line that runs the length of their body that is able to
detect changes in water pressure. It helps them feel movements in the
water around them.
(Photo: Jane West)
Jacobsen’s organ
This organ is found in snakes. It is located on the roof of the mouth.
The snake’s forked tongue collects chemicals from the air and presses
them into the organ.
Electric fields
Sharks and some fish track prey by the weak electric fields created in
water. The platypus has electroreceptors in its bill. It uses weak electric
fields to locate prey. The African Electric fish is nocturnal and lives in
murky water. It sends out 300–400 pulses of electricity per second.
It can detect any change in the electric field to locate prey.
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Communicating with the senses
Not all senses are used in communication, however the main senses used
in communication are:
•
hearing (auditory)
•
sight (visual)
•
smell (olfactory)
•
touch (tactile).
Auditory
Often if you go for a walk in the bush you will hear the sounds of many
animals. Usually it is the sounds of animals rather than the sight of them
that is obvious. In the early morning and evening many birds and insects
call to communicate. They may be declaring their territory, alerting
others of a predator or searching for a mate. There are even many sounds
that you can’t hear such as the ultrasonic call of some moths and bats.
An advantage of auditory signals is that the message can travel great
distances. For example, howler monkeys and siamangs call through the
tropical forests declaring their territory. Another advantage of sound
communication is there is no need to be close to communicate by sound.
Visual
Visual displays include body posture, colour, facial expression and
threatening behaviour. The plumage of birds is used in display
and courtship.
A male gorilla will defend his territory by beating his chest and making
aggressive movements. This visual display scares off intruders without
the need for actual physical violence.
Birds use visual displays to great effect. They have four types of colour
receptors on their retinas, one more type than humans. They can see
colour in another dimension. This may explain why some birds have
colourful plumage.
Smell
Olfaction (the sense of smell) is one of the oldest senses in evolutionary
terms. It is the detection of chemicals in the environment. This ability is
used by predators to locate prey and by prey to escape predators.
Part 1: Making sense of your surroundings
9
Many animals use the sense of smell to find sexual partners and to avoid
predators. Scent marking is used to declare territories.
Human sense of smell is limited but animals such as dogs live in a world
of smells. If you have taken your dog for a walk you would have noticed
how interested the dog is in all the smells that abound. Dogs mark their
territory by urinating on prominent objects. They can tell if a female dog
is on heat by the odour given off.
The chemicals that carry messages are called pheromones. They are
signaling molecules. They can tell an individual’s identity. For insects
chemical communication is highly developed. A male moth can detect a
female moth more than a kilometre away. The amount of pheromone can
be very small. In the case of the moth the male only requires to detect
one molecule of the female pheromone to fly off and find her.
Queen bees give off pheromones that prevent the worker bees
becoming sexually mature.
Ants communicate in many ways using pheromones. In ant colonies
pheromones are used to trigger attacks, set trails, exchange food, defend
their territory and control reproduction. Insect pheromones are so
powerful that they are used to control pest species in agriculture.
Female pheromones are released over crops to confuse and overload the
males with stimuli and prevent mating.
Insects have olfactory organs on their antenna to detect odours.
Some have more than 100 000 sensory hairs. Rodents have powerful
responses to pheromones. The golden hamster will give up mating
completely if the olfactory part of the brain is removed.
Tactile
When animals use the sense of touch they are close together.
Therefore it is used in fighting and in courtship behaviour.
Many mothers and infants communicate by touching.
Touching is very important in communicating group bonding especially
in primates. Chimpanzees greet each other by shaking hands.
They groom each other for hours. Horses rub noses apparently to
show affection.
Bees dance to communicate the location of a food source. They give
information on both the distance and direction. This occurs in the
darkness of the hive.
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Taste
Poisonous animals sometimes have an unpleasant taste to communicate
to a predator that they are not to be eaten. Humans do not use taste as a
form of communication.
Identify data sources, gather and process information from secondary
sources to identify the range of senses used in communication.
Hint
Find a data source to identify the range of senses used in communication.
This could be on the Internet, a book or a popular scientific journal.
Identify the data source using the referencing system given in the
Additional resources section at the back of this part.
Write the reference that you have found in the space below.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Summarise the information above by placing it in the table in Exercise 1.2.
Part 1: Making sense of your surroundings
11
Visual communication
By far the most important sense organ in humans is the eye. Not only is
the detection of light images important for survival but also the
perception of colour and depth are absolute necessities for some animals.
Visual communication involves the eye registering changes in the
immediate environment.
Anatomy and function of the
human eye
The structure of the eye is delicate and complex. It makes sense of
the light stimuli streaming into it every waking hour of the day.
The anatomy of the eye consists of three layers. The outer layer
consists of the sclera which surrounds the eye and the cornea at the
front of the eye.
sclera
retina
cornea
(Photo: Jane West)
The sclera is the dense white layer of the eye. It protects the eye.
The cornea is the clear jelly-like front of the eye. It protects the front of
the eye and focuses light entering the eye.
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The middle area of the eye consists of the dark pigmented choroid layer.
This membrane layer prevents light from scattering by absorbing light.
It contains the blood vessels that nourish the eye. Suspended from the
choroid layer is the pigmented iris. The iris is a muscular structure that
controls the amount of light that enters the eye by changing the size of
the pupil. The pupil is the hole in the centre of the iris.
Behind the iris is the lens which consists of layers of transparent
proteins. The lens is responsible for the fine focus of light on to the back
of the eye. The lens is moved by the ciliary muscles. The ciliary
muscles and the suspensory ligaments are located in the ciliary body this
links the choroid to the lens. In front of the lens is a clear watery fluid
called the aqueous humour (also spelt aqueous humor). This fluid
transmits light and maintains the pressure of the eye. Behind the lens in
the centre of the eye is the vitreous humour (vitreous humor).
This jelly-like substance allows light to travel through to the back of the
eye and maintains the shape of the eye. The conjunctiva is a
continuation of the epidermis, it covers the surface of the eye and
protects the cornea.
conjunctiva
lens
retina
aqueous
humour
pupil
iris
choroid
ciliary body
vitreous humour
The inner layer of the eye consists of the retina, which detects light with
light sensitive cells (photosensitive), the fovea the area of greatest visual
acuity and the start of the optic nerve. The optic nerve carries the
nervous impulses from the retina to the visual cortex in the brain.
Where the optic nerve leaves the retina is the blind spot. There are no
photoreceptors at that point.
Part 1: Making sense of your surroundings
13
retina
retina
fovea
blind spot
optic nerve
Optional activity: test your blind spot
You can find your blind spot by performing this activity using the
diagram below. Cover your left eye and stare at the cross. You will be
able to see the circle in the periphery of your view. Don’t look at the
circle. Move the page in and out as you look at the cross. The circle will
disappear when the image of the circle is focused on the blind spot.
Try the same with the other eye. This time cover your right eye and look
at the circle.
Do Exercise 1.3 now.
Visit the LMP Science Online webpage for this module to see an interactive
version of the eye diagram at: http://www.lmpc.edu.au/science
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Investigation of a mammalian eye
You have been reading about the structure of an eye now it’s your chance
to examine one in more detail.
Plan, choose equipment or resources and perform a first-hand investigation
of a mammalian eye to gather first-hand data to relate structure to functions.
Hint
Plan your experiment and choose your equipment or resources from the
materials you have available to you. Predict possible issues that may
arise during the experiment. In this case there is a risk assessment
necessary to predict the dangers of using sharp instruments. Address the
potential hazards that may occur. Plan what you will do with waste
material from the experiment and have equipment such as a disposal
plastic bag ready to be used. As you do the dissection try to relate the
structures that you are seeing to the function they perform in the eye.
If you are unable to do the dissection then use the photographs below or see
them in colour at the LMP Science Online web site for this module at:
http://www.lmpc.edu.au/science
Planning
You can order cow’s eyes at a butcher shop or purchase them directly
from abattoirs. Try to get eyes with the muscles and fat still attached.
If possible pick up the cow’s eyes the day of the dissection; eyes are
easier to cut when they are fresh.
There are some risks to assess in this activity. You will be dealing with
animal tissue so make sure that you wear rubber gloves. You will also be
using sharp instruments so be aware of the dangers of cutting yourself.
When you have finished dispose of any waste by wrapping in paper and then
place in a plastic bag before placing in the garbage bin. Wear appropriate
clothing including covered footwear during the activity. Risk of any
infection from the material is very unlikely. In some overseas countries
where BSE (bovine spongiform encephalitis or mad cow disease) is
common there may be a slightly higher risk of infection and more care is
need to be taken with the disposal of the material.
Part 1: Making sense of your surroundings
15
Materials required:
•
one single-edged razor blade, knife or scalpel
•
scissors (optional)
•
paper towels
•
plastic garbage bag
•
rubber gloves.
Procedure
Examine the outside of the
eye. See how many parts of
the eye you can identify.
You should be able to find
the whites (or sclera)
and the clear covering over
the front of the eye (the
cornea). The conjunctiva is
the outer membrane covering
the cornea.
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You should also be able to
identify the fat and muscle
surrounding the eye.
Return your attention to the
outside of the eye. Locate
the optic nerve. To see the
separate fibers that make up
the optic nerve, pinch the
nerve with a pair of scissors
or with your fingers.
Make the first incision where
the sclera meets the cornea.
Cut until the aqueous humour
is released. Rotate the eye
and cut around the cornea.
Be careful not to cut too deep
or you may cut the lens. As
the cornea starts to come
free, hold the cornea in the
centre and make the last cuts
around it.
Once you have removed the
cornea, place it on the board
(or cutting surface) and cut it
with your scalpel or razor.
With the cornea removed, the
next step is to pull out the
iris. Place one finger in the
centre of the eye. Find the
iris and pull it back. It
should come out in one
piece.
Part 1: Making sense of your surroundings
17
It can be a bit tricky to
remove the lens with the
vitreous humour attached. It
works best if you cut slits in
the sclera. Be careful not to
cut the lens.
After enough incisions have
been made in the sclera, you
should be able to remove the
lens. Sometimes the vitreous
humour will be removed
along with the lens. Hold up
the lens and look through it.
If the lens is too slippery, pat
it dry with the paper towel
and try again.
With the vitreous humour
now removed, you should be
able to turn the eye inside
out.
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The thin tissue on the back of
the eye is the retina. Find the
blind spot where the optic
nerve is attached.
Results
Draw a diagram of your dissection (or use the one above) in the space
below. Show the optic nerve, cornea, sclera, lens, retina and the
blind spot.
Conclusion
Describe the functions of each structure of the eye, and hoe each
structure is suited to perform that function.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Part 1: Making sense of your surroundings
19
Detection of energy
An animal senses light using the properties and specialised nature of
light. The light detecting receptors of the eye (called photoreceptors)
can pick up certain wavelengths of energy which we call visible light.
To understand more fully how animals detect and communicate light
you must first learn a bit about the nature of this peculiar type of energy.
Light comes from various sources. Can you list some?
The most important source is the sun. Things like fire, electric lights and
glowing hot objects all produce light. Some animals produce light.
This is known as bioluminescence.
Light is a form of electromagnetic radiation (EM). Light energy is
similar in lots of ways to other forms of energy like heat, ultraviolet
radiation, microwaves and X-rays.
The diagram below shows how these various forms of energy are
distinguished by their wavelengths (measured in nanometres, nm).
gamma
rays
x-rays ultraviolet
infra-red
light
radio waves
microwaves TV
radio
electrical
power
1 cm
1m
1 km
103 km
10–2
100
103
106
Wavelength
0.01 nm
Wavelength in metres
10–11
1 nm
0.1 mm
0.01 mm
0.4–0.7mm
10
–9
10
–7
10–5
The diagram shows that energy is made up of vibrating waves of various
wavelengths. Each wavelength represents a different kind of
electromagnetic radiation. Even light energy is a mixture of different
wavelengths we call colour. Violet light waves are about 380 nm while
red light waves are larger at about 700 nm. Below 380 nm is ultraviolet
and above 700 nm is infra-red neither of these is visible to humans.
Human vision is limited to the visible light range.
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White light is a combination of what is perceive as coloured light.
In 1666 Isaac Newton separated white light into the spectrum of colours
using a glass prism demonstrating that white light is made up of a
mixture of colours.
prism
gamma
rays
10
-5
10
x-rays
rays
-3
10
-1
ultra
violet
rays
10
1
infrared
rays
10
3
10
0.7
ye
llo
w
re
d
0.6
gr
ee
n
bl
ue
0.5
in
di
go
vi
ol
et
0.4
radar
5
10
7
broadcast bands
10
9
10
11
10
13
AC circuits
10
15
10
17
You can view this diagram in colour on the LMP Science Online web site
for this module at: http://www.lmpc.edu.au/science
The range of colour vision that humans perceive is from 390 to 750 nm.
It is very important at this stage for you to understand that the human eye
only senses the range of colour vision from violet to red. Violet light has
the shortest wavelength and the most energy while red light has a longer
wavelength. The most effective wavelength for human vision is around
500 nm, which is blue-green light.
Wavelength of light (nanometres)
Colour
Less than 390
non-visible ultraviolet
390
violet
450
blue
500
blue-green
550
green
570
yellow
600
orange
750
red
Greater than 750
non-visible infra-red
Part 1: Making sense of your surroundings
21
What is the limited range of wavelengths detected by humans?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
Vision ranges
It is important for you to know that not all animals perceive the same
range of wavelengths of electromagnetic radiation as people. The range
of wavelengths that is biologically important for vision is 300–850 nm.
Above 850 nm there is not enough energy to excite the photoreceptors
and below 300 nm the amount of energy is so great that it can destroy the
sensitive photoreceptors.
Many arthropods such as bees, ants and spiders and some vertebrates
such as the Japanese Dace fish, carp and goldfish use the ultraviolet
range (300 to 400 nm) for vision. Butterflies and other flying insects can
see landing lines on flowers using UV vision. To human vision the
landing strips are invisible.
Sharks have almost no colour vision. Sea turtles have good vision for
reds and yellows but not for blues and greens. Dogs see muted colour
but make up for this with greater movement sensitivity and night vision.
Snakes can see in two ways. Firstly they have their eyes to see using the
visual range and then they have infra-red receptors located in pit organs.
These pit organs are usually located on the head or along the jaw.
They are sensitive to heat given off by other animals. It allows them to
locate prey even in the dark.
To see the world through infra-red receptors visit the LMP Science Online
web site for this module at: http://www.lmpc.edu.au/science
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So, there is a range of wavelengths that are detected by animals ranging
from the ultraviolet to the infra-red. The table below summarises some
of this information.
Organism
Example
Wavelength
range
(nanometres)
Part of the
EM
spectrum.
invertebrate
bee
340–540
UV and
visible
ant
340–540
UV and
visible
human
390–750
visible
carp
360–700
UV and
visible
pit viper
400–850
infra-red and
visible
deep sea
fish
470–480
visible
pigeon
360–500
near UV and
visible
vertebrate
Do exercise 1.4 now to complete this first part of the module.
Part 1: Making sense of your surroundings
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Summary
During this part of the module you should have carried out the following
first-hand investigations and other tasks using secondary information.
First hand investigations
Make sure you can describe how you did the following first-hand
investigations. List the precautions that need to be taken during the
experiments and the safe working practices you used.
•
Plan, choose equipment or resources and perform a first-hand
investigation of a mammalian eye to gather first-hand data to relate
structures to functions.
Secondary information
•
Identify data sources, gather and process information from
secondary sources to identify the range of senses involved in
communication.
•
Use available evidence to suggest reasons for the differences in
range of electromagnetic radiation detected by humans and other
animals.
Summary of content
•
Communication is the transfer of information from a sender to a
receiver.
•
Receptors are specialised cells whose role is to detect stimuli.
•
Examples of receptors are photoreceptors (light), chemoreceptors
(chemicals) and thermoreceptors (temperature).
•
Some receptors are used in communication.
Part 1: Making sense of your surroundings
25
•
A stimulus – response pathway is:
stimulus
receptor
messenger
effector
response
muscle
contracts
bright light
26
sensory cells
in eyes
nerve
muscle
•
The electromagnetic spectrum visible to humans ranges from
390–750 nm.
•
Other organisms such as snakes can see into the infra-red range,
insects can see ultraviolet light.
•
The structure of the eyes consists of the conjunctiva, cornea, sclera,
choroid, retina, iris, lens, aqueous and vitreous humour, ciliary body
and optic nerve.
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Suggested answers
Here are suggested answers for many of the questions from
throughout this part. Your answers should be similar to these answers.
If your answers are very different or if you do not understand an answer,
contact your teacher.
Detecting stimuli
1
Human senses are sight (visual), hearing (auditory), smell
(olfactory), touch (tactile) and taste (gustatory).
2
The human sense organs are eyes, ears, nose, skin and tongue.
Detection of stimuli
The range of human vision is from violet to red in the visible spectrum.
The wavelength of waves is 390 to 750 nanometres.
Part 1: Making sense of your surroundings
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Additional resources
Citing References
There are certain standard ways of writing a reference list. Here are
some suggestions.
For a book
•
List the reference alphabetically by the author’s surname.
•
Use initials for the author’s other names.
•
Follow this with the date of publication in brackets.
•
Put the title of the book in italics (if typed) or underline the title if
handwritten.
•
List the publisher.
•
Give the pages that were useful.
Example
Brown, A and Smith, A (1985): Apples. Heinemann Ed Aust.
pp 224–250.
Internet sites
•
As these are constantly changing you should give as much
information as you can.
•
Give the web address, the author and the date accessed
where possible.
Example
Burbank, H. (accessed May 2001): ‘Environmental Resource Room’
http://www3.umassd.edu/Public/Exhibit/DES300/currmat2.html
Part 1: Making sense of your surroundings
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Scientific Journals
•
Author’s surname and initials.
•
The date of publication in brackets.
•
Name of the article.
•
Name of the journal underlined.
•
The volume and series of the journal.
•
The page numbers.
Example
Brown, R.J (1997): Fish recruitment in seagrass beds of NSW. Aust Fish
Biology 52(1), 57–65.
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Exercises – Part 1
Exercises 1.1 to 1.4
Name: _________________________________
Exercise 1.1: The role of receptors
a)
Identify the role of the receptors in detecting stimuli.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) Explain the knee jerk reaction in response to striking the kneecap.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
c)
Look at the diagram below. It has the reactions that occur as your
eye sees a bright light.
muscle
contracts
bright light
sensory cells
in eyes
nerve
muscle
Describe the process shown in the diagram.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 1: Making sense of your surroundings
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Exercise 1.2: Senses in communication
Fill in the table below where possible.
Sense
Example of communication in animals
sight
hearing
touch
smell
taste
other
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Exercise 1.3: The human eye
Fill in the names for the structure of the eye using the following terms:
conjunctiva, choroid, sclera, vitreous humour, fovea, ciliary body, cornea
pupil, retina, iris, lens, aqueous humour, optic nerve, blind spot.
retina
Complete this table.
Part of the eye
Function
conjunctiva
cornea
sclera
choroid
retina
iris
Part 1: Making sense of your surroundings
33
lens
aqueous humour
vitreous humour
ciliary body
optic nerve
Exercise 1.4: The range of vision
a)
Identify the limited range of wavelengths of the electromagnetic
spectrum detected by human eyes.
______________________________________________________
______________________________________________________
______________________________________________________
b) Give an example of an animal that can detect electromagnetic
wavelengths outside the range of human perception. State the range
of vision for your example.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
c)
A pit viper can find its prey even in the darkness of a burrow.
How does this organism detect its prey?
______________________________________________________
______________________________________________________
______________________________________________________
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d) List three parts of the electromagnetic spectrum that humans cannot
detect with their senses.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 1: Making sense of your surroundings
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Biology
HSC Course
Stage 6
Communication
Part 2: Eye can see clearly
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20
I
er
b
to T S
c
O EN
g
in D M
t
a
r EN
o
p
or AM
c
n
2
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Contents
Introduction ............................................................................... 2
The nature of light ..................................................................... 3
Refraction .............................................................................................3
Bending light with your eyes ................................................................6
Accommodation......................................................................... 7
Modeling accommodation....................................................................8
The refractive power of the lens .......................................................11
Visual impairment ................................................................... 14
Hyperopia ..........................................................................................14
Myopia ...............................................................................................15
Correcting technologies ....................................................................16
Cataracts ...........................................................................................18
Summary................................................................................. 21
Suggested answers................................................................. 23
Exercises – Part 2 ................................................................... 25
Part 2: Eye can see clearly
1
Introduction
The eye needs a clear image of both nearby and far away objects.
This part of the module explains how the nature of light and the structure
of the eye work together to enable you to see things clearly.
In this Part you will be given opportunities to learn to:
•
identify the conditions under which refraction of light occurs
•
identify the cornea, aqueous humor, lens and vitreous humor as
refractive media
•
identify accommodation as the focusing on objects at different
distances, describe its achievement through the change in curvature
of the lens and explain its importance
•
compare the change in the refractive power of the lens from rest to
maximum accommodation
•
distinguish between myopia and hyperopia and outline how
technologies can be used to correct these conditions.
In this Part you will be given opportunities to:
•
plan, choose equipment or resources and perform a first-hand
investigation to model the process of accommodation by passing
rays of light through convex lenses of different focal lengths
•
analyse information from secondary sources to describe changes in
the shape of the eye’s lens when focusing on near and far objects
•
process and analyse information from secondary sources to describe
cataracts and the technology that can be used to prevent blindness
from cataracts and discuss the implications of this technology
for society.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Amended November 2002. The most up-to-date version can be
found on the Board’s website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_listb.html
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The nature of light
The fact that light bends when passing between clear media like
water, glass or plastic has shaped the evolution of the eye into the
complex structure you see today. Light usually travels in straight lines.
The process whereby light bends when it enters a different transparent
medium is called refraction.
This section will help you identify the conditions under which refraction
of light occurs.
Refraction
Refraction is the phenomenon where light appears to bend as the light
rays pass from one medium to another. You have seen the bending effect
when you put a straight stick into clear water such as a fish tank.
This apparent bending effect is shown below. In this case, you are seeing
the refraction of light rays.
observer
apparent bend
surface
apparent position
of stick
water
Diagram showing the image of a stick in water showing refraction.
When spearing a fish an experienced hunter would throw the spear below
where the fish appears to be swimming to hit the fish.
Part 2: Eye can see clearly
3
The scientific understanding of refraction is based on the following facts.
•
As light travels through a given medium, it travels in a straight line.
•
When light passes from one kind of medium into a second medium
with a different optical density, the light path bends. This is
refraction.
•
The refraction occurs only at the boundary. Once the light has
crossed the boundary between the two media, it continues to travel in
a straight line; only now, the direction of that line is different than it
was in the former medium.
normal
The diagram shows refraction or bending of a beam of light as it passes into
material of different density.
Try this demonstration of refraction.
Take a ceramic bowl, a coin and a glass of water. Place the coin in the
bottom of the bowl and move your head so that you are viewing the bowl at
such an angle that you can just no longer see the coin.
See the diagram following.
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angle of
view
angle of
view
bowl
coin
Now add more water to the bowl.
What did you observe to happen as you poured more water into the bowl?
_________________________________________________________
Explain your observations using your knowledge of refraction.
_________________________________________________________
_________________________________________________________
Check your answer.
The whole shape of your eye is designed to make use of refraction in
order to see more clearly.
Part 2: Eye can see clearly
5
Bending light with your eyes
In Part 1 of this module you looked at the structure of the eye.
Which parts are made up of a transparent (clear) medium? You may
remember that the parts called the aqueous and the vitreous humour are
in fact very clear and the cornea is often called the window to the eye.
The lens is also a transparent medium. Each of these parts has a different
density therefore as light passes through them they will refract or
bend light.
The four refractive media found in the eye are:
•
cornea
•
aqueous humour
•
lens
•
vitreous humour.
The result of this refraction is that as light travels through these structures
it bends or refracts in such a way as to focus the light on the retina.
Have a good look at the diagram below. Notice the way light bends so
that it is focused on the retina. The greatest amount of bending occurs at
the cornea-air surface.
lens
aqueous humour
vitreous humour
cornea
The cornea, aqueous humour, lens and vitreous humour are all refractive media
found in the eye.
Do Exercise 2.1 now.
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Accommodation
To enable objects at different distances to be viewed clearly, your eyes
have evolved a method of focusing the image on your retina no matter
where the image is located.
The ability of your eyes to change focus so that objects can be seen
sharply at varying distances is called accommodation. When the lens of
your eye alters to make an image clear and focused, the eye is said to be
accommodated. Try this simple activity with your eyes.
•
Hold your finger up in front of you and look at it so that the finger is in
focus. Depending on your eyesight this could be as close as 25–30 cm.
•
While keeping your finger in focus, observe the objects behind and
further away from your finger. Write down what you notice about
the clarity of these objects.
_____________________________________________________
•
Now focus your vision on a far object while keeping your finger in
exactly the same position. Describe the clarity of your finger while
focusing on the background.
_____________________________________________________
Part 2: Eye can see clearly
7
When focusing on the near object the
distant object is blurred.
When focusing on the distant object
the near object is blurred.
Your eyes can change focus but cannot have everything in focus at the
same time.
Types of lenses
The lens found within the eye is a convex lens. It bulges out in the centre.
An other type of lens is a concave lens. This type of lens goes in at
the center.
Convex lens
Concave lens
Modeling accommodation
A good way to model accommodation is to pass parallel rays of light
through some convex lenses. A convex lens converges (brings together)
light into a focal point. The distance from the lens to the focal point is
called the focal length. The curvature of the lens is responsible for
the focal length. The greater curvature of the lens the shorter the
focal length.
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convex lens
parallel light
F'
focal length
If you have several convex lenses you could shine light through them and
record the focal length for each lens.
Different curvature of a convex lens
In this activity you will measure the focal length of two convex lenses.
The focal length is the distance from the middle of the lens to the point
where the light rays converge. Mark on the diagrams the focal point of each
lens. Now use the grid squares (1 cm) to estimate the focal length of each
lens below by counting the squares from the middle of the lens to the
focal point.
Convex lens 1
Convex lens 2
Part 2: Eye can see clearly
9
Feature
Lens 1
Lens 2
Focal length
Curvature of lens
From the two lenses above what is the relationship between the curvature
of the lens and the focal length?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answers.
On the LMP Science Online webpage there are instructions on how to use a
light box to examine the behaviour of lenses. You can do the above exercise
online in colour if you prefer at: http://www.lmpc.edu.au/science
If you don’t have access to convex lenses then you can model
accommodation in the eye by using drops of water of different thickness
in the activity below.
In this activity you will need a firm sheet of clear plastic such as a CD cover
or a piece of glass like a microscope slide. You will also need access to
water drops.
Procedure
•
Place a drop of water on your sheet of plastic or piece of glass.
drop of water
10
clear plastic or glass
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Notice how you can make a thin drop or a fat drop.
•
Start with a fat drop and hold it over some printing such as a
newspaper.
•
Move the drop up and down to see the distance required to focus the
writing on a sheet of newspaper.
print media
Now make a thin drop and note the different distance required to focus
the print.
thin drop of water
clear plastic or glass
The fat and the thin drop of water models the changing shape of the eye’s
lens. They are examples of convex lenses. The fatter drop should have
had a shorter focal length than the thin drop of water.
The lens is responsible for fine focusing the image onto the retina while
the cornea is responsible for most of the refraction of light in the eye.
Likewise the lens of the eye assumes a large curvature (short focal
length) to bring nearby objects into focus and a flatter shape (long focal
length) to bring a distant object into focus.
The refractive power of the lens
The importance of accommodation is the ability of the eye to change the
shape of the lens and focus on objects whether they are near or far.
This is achieved by the contraction of the ciliary muscles in the
ciliary body.
Part 2: Eye can see clearly
11
Maximum accommodation
When the ciliary muscles contract the suspensory ligaments, that hold the
lens are released and the lens becomes more rounded. This is fully
accommodated and maximum refraction of light. Near objects would be
in focus.
At rest
When the ciliary muscles relax the suspensory ligaments are taut and the
lens is flattened. Vision would be focused on far objects and the
refractory power would be at a minimum.
Distance focused eye:
• ciliary muscles relaxed
• suspensory ligaments tight
• lens is flattened
• minimum accommodation
Close focused eye:
• ciliary muscles contracted
• suspensory ligaments loosened
• lens is rounded
• maximum accommodation
Process and analyse information form secondary sources to describe changes
in the shape of the eye’s lens when focusing on near and far objects.
Hint
A good way of processing information on the changes in the shape of eye’s
lens during accommodation is to draw a diagram like the one above.
The diagram should show the contraction and the relaxation of the ciliary
muscles and the suspensory ligaments. It should also illustrate the change in
shape of the lens through these actions.
On the LMP Science Online web site there is an animation that shows
accommodation and the change in the shape of the lens. If you have access
to the Internet visit the site and have a look at the animation. Use this as a
secondary source of information. Analyse the animation by writing a
description of the changes that occur as the object gets closer to the lens.
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Drawing of the shape the eye’s lens when focusing on close or
distant objects.
Distance focused eye
Close focused eye
Write your description of accommodation in the space below.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Do Exercise 2.2.
Part 2: Eye can see clearly
13
Visual impairment
You have just learnt that to focus on nearby objects requires a different
lens shape to that required for focusing on distant objects. People with
clear vision have eyes where the lens adjusts correctly in all situations.
For people who can’t see clearly in some situations the problem is caused
by their eye’s inability to focus light directly on the retina.
Glasses (or contact lenses) are used to change the way light is refracted
so objects appear in focus. People who wear glasses have a problem with
seeing things clearly either close up or far away.
In this section you are required to distinguish between the two main
kinds of eye focusing conditions, namely myopia and hyperopia.
You might even have one of these conditions yourself - they are
commonly known as short-sightedness and far-sightedness.
Cataract, a clouding of the lens causing blurred vision, is another type of
visual impairment. The technology used to prevent blindness from
cataracts is also detailed and you will be required to discuss the
implications of this technology for society.
Hyperopia
Far-sightedness is the inability of the eye to focus on objects that are
close. The proper term for this is hyperopia. The far-sighted eye has no
difficulty viewing distant objects. There is a problem however, when
people with hyperopia view objects close to the eye.
The lens of the far-sighted eye can no longer assume the very rounded
shape required when viewing nearby objects. This causes these images
to be focused at a location behind the retina meaning the light-detecting
cells will perceive a blurred image. The problem is most common during
later stages in life because of the weakening of the ciliary muscles and
the decreased flexibility of the lens.
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light is focused behind the retina
In hyperopia a close object produces a blurred image because the lens cannot
produce the rounded shape necessary to bend light sufficiently to focus the
image on the retina.
Myopia
Short-sightedness or myopia is the inability of the eye to focus on distant
objects. The short-sighted eye has no difficulty viewing nearby objects
yet the ability to view distant objects is a problem. This is because the
light from distant objects is bent or refracted more than is necessary.
The problem is most common as a youth, and is usually the result of a
bulging cornea or an elongated eyeball.
light is focused in front of the retina
A short-sighted person viewing a distant object focuses the image in front of
the retina.
If the cornea bulges more than its customary curvature, then it tends to
refract light more than usual. The images of distant objects are focused
in front of the retina. If the eyeball is elongated in the horizontal
direction, then the retina is placed at a further distance from the
cornea-lens system; subsequently the images of distant objects form in
front of the retina. On the retinal surface, where the light-detecting cells
are located, the image is not focused. The nerve cells thus detect a
blurred image of distant objects.
Part 2: Eye can see clearly
15
Correcting technologies
Eyeglasses or spectacles and contact lenses are the most common way to
correct these conditions.
Correcting hyperopia
In order to correct the far-sighted eye, some devise must be used to
refract the light. Since the lens can no longer change to the highly
curved shape required to view nearby objects, it needs some help.
The far-sighted eye is assisted by the use of a convex lens that will
converge the light rays further.
A convex lens converges light rays and corrects the problem of hyperopia.
This converging lens will refract light before it enters the eye and
therefore enable the eye to focus light onto the retinal surface. This is
explained in the diagram below.
lens converges the image
A convex lens corrects the problem of hyperopia by focusing the image
onto the retina.
Correcting myopia
The nature of the problem of nearsightedness is that the light is focused
in front of the retina. Light can be refracted artificially using a lens
which diverges the light rays just enough so that it focuses on the retina.
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Hence the cure for the nearsighted eye is to equip it with a diverging lens
called a concave lens. See the diagram below.
lens converges the image
A concave lens corrects the problem of myopia. Note that the lens is still
curved outwards at the front but has a much deeper curvature at the back.
A concave lens diverges light rays.
A diverging lens acts on the light rays before it reaches the eye.
This light will be converged by the cornea and lens producing a focused
image on the retina.
There are also more permanent methods for correcting sight problems.
Surgical modification of the cornea
Refractive laser surgery can be used to change the shape of the cornea
permanently so that it converges or diverges the light enough to correct
the condition. During this surgery a flap of the cornea is cut and lifted
and a laser beam is used to reshape the rest of the cornea, the flap of
tissue is then replaced.
The original corrective eye surgery was known as radial keratotomy or
the ‘Russian Operation’ because of its inventor. Recent advances in laser
surgery have changed the technique. An ultraviolet-argon laser breaks
intermolecular bonds and thin layers are removed from the cornea
Part 2: Eye can see clearly
17
reshaping the curvature of the cornea. The process is computercontrolled for greater accuracy.
Do Exercise 2.3.
Cataracts
The lens of the eye is made up mostly of water and protein. The protein
is arranged to allow light to pass freely. Sometimes the protein clumps
together clouding small areas of the lens. This obstructs light from
reaching the retina causing vision problems and is called a cataract.
A cataract is a progressive clouding of the lens and happens over a
prolonged period of time. The amount of visual impairment depends on
how much clouding of the lens occurs. The degree of cataract formation
depends on factors such as age, lifestyle or diseases like diabetes.
The technology used to prevent blindness
from cataracts
The technology used to prevent blindness from cataracts is the
replacement of the cloudy lens with an artificial intraocular lens (IOL).
There are three methods of cataract surgery:
•
phacoemulsification
•
extracapsular extraction
•
intracapsular extraction.
Phacoemulsification is the most common technique. A small incision is
made where the cornea meets the sclera. A probe is inserted that emits
high frequency vibration that breaks the lens into pieces. The lens is then
suctioned out and replaced with an intraocular lens. The incision is so
small that usually stitches are not required. The operation is very
successful and millions of these operations take place each year.
The other methods are used when the lens does not break up easily.
Fred Hollows Foundation
The social implication of the technology of cataract treatment can be
seen in the work of the Fred Hollows Foundation. Cataract blindness is
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found all around the world. It is estimated that 20 million people in
developing countries are suffering blindness caused by cataracts.
An older person who develops cataracts in a developing country usually
only lives for a few years after blindness sets in. By returning sight to
these people their lives are prolonged and the quality of their existence is
greatly improved.
The operation needed to cure cataract blindness is simple and only takes
about fifteen minutes. People in developing countries cannot afford the
operation without assistance. Fred Hollows trained local doctors in
countries such as Nepal, Vietnam and Eritrea to replace the clouded lens
of cataract sufferers with an artificial lens. Since his death his foundation
has set up factories to produce cheap affordable lenses. During his
lifetime Fred Hollows helped a quarter of million people to see again and
the work is continued by his foundation.
Process information from secondary sources to describe cataracts and the
technology that can be used to prevent blindness from cataracts and use
available evidence to discuss the implications of this technology for society.
There are some useful sites to be found on the Internet. Use a search engine
and search for secondary information using terms such as ‘cataracts’ and
‘cataract surgery’. For the social implications of the technology search for
information using search words like ‘Fred Hollows foundation’.
There are also some useful sites gathered for you on the LMP Science
Online webpage that can be accessed at: http://www.lmpc.edu.au/science
If you do not have Internet access then library books or a letter written to the
Fred Hollows Foundation would be a good source of secondary information.
Process the information that you gather by answering the
following questions.
1
What are cataracts?
2
How do they form?
3
What technology can be used to prevent blindness?
4
How would you search for secondary information to describe
cataracts and the technology used to prevent blindness?
Do Exercise 2.4 to complete this part of the module.
Part 2: Eye can see clearly
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Summary
During this part of the module you should have carried out the following
first-hand investigations and tasks using secondary information.
First hand investigations
Make sure you can describe how you did the following first-hand
investigation. List the precautions that need to be taken during the
experiments and the safe working practices you used.
•
Plan choose equipment or resources and perform a first-hand
investigation to model the process of accommodation by passing
rays of light through convex lenses of different focal lengths.
Secondary information
•
Process and analyse information from secondary sources to describe
changes in the shape of the eye’s lens when focusing on near and
far objects.
•
Process and analyse information from secondary sources to describe
cataracts and the technology that can be used to prevent blindness
from cataracts and use available evidence to discuss the implications
of this technology for society.
Summary of content
•
Refraction is the bending of light as it moves into a
different medium.
•
The cornea, aqueous humour, lens and vitreous humour are
refractive media found in the eye.
•
The result of the properties of light is the image focused on the retina
is upside down, back to front and much smaller than the original
image. The brain is able to interpret this information and you see the
world the right way up.
Part 2: Eye can see clearly
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22
•
Accommodation is the ability to focus objects at different distances
through a change in the curvature of the lens by the contraction of
the ciliary muscles.
•
The lens at rest focuses on distance objects, the ciliary muscles are
relaxed, the suspensory ligaments are taut, the refractive power is at
a minimum and the lens is flatter. At maximum accommodation the
lens is rounded, the refractory power is at its greatest, the ciliary
muscles are contracted and the suspensory ligaments are loose.
•
Myopia is short-sightedness, the image of far objects is blurred
because the refractory power of the lens is too great and the image is
focused in front of the retina.
•
Hyperopia is far-sightedness, close objects are blurred because the
image is focused behind the retina.
•
The technologies that are used to correct these conditions are lenses
such as glasses and contact lenses and refractive eye surgery to
change the shape and refractory power of the cornea. A concave
lens is used for myopia and a convex lens for hyperopia.
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Suggested answers
Refraction
As you add more water the coin becomes visible.
More water has increased the angle of refraction.
Accommodation
When your finger is in focus the objects behind are blurred.
In the second case the image of the finger is blurred while the
background is in focus.
The curvature of a convex lens
Feature
Lens 1
Lens 2
Focal length (cm)
4.5
7.3
Curvature of lens
more curved
less curved
The relationship between the curvature of the lens and the focal length is
that the greater the curvature the less the focal length.
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Exercises - Part 2
Exercises 2.1 to 2.4.
Name: _________________________________
Exercise 2.1: Refraction
a)
What is refraction?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) Under what conditions does refraction occur?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
c)
Name the refractive media found in the eye.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
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d) On the diagram following label the cornea, aqueous humour, lens
and vitreous humour and mark with a cross the four points where
refraction occurs.
Exercise 2.2: Accommodation
a)
What is accommodation in the eye?
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
b) How does the eye change the focus from distant to near objects?
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
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c)
Use the following words to fill in the blanks below.
minimum ciliary relaxed rounded distances focus contracted
Accommodation is the ability to __________ objects at different
____________ through a change in the curvature of the lens by the
contraction of the_____________________muscles.
The lens at rest focuses on distance objects, the ciliary muscles
are________________, the suspensory ligaments are taut, the
refractive power is at a ____________ and the lens is flatter. At
maximum accommodation the lens is _____________, the refractory
power is at its greatest, the ciliary muscles are ____________ and the
suspensory ligaments are loose.
d) Describe the change in the shape of the lens when focusing on near
and far objects.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
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d)
Look at the diagrams below and circle the eye that is focused on a
near object. Give three reasons for your answer.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Exercise 2.3: Visual impairment
a)
Distinguish between myopia and hyperopia.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
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b) What sort of lens is required to help a person with myopia?
_____________________________________________________
_____________________________________________________
c)
What sort of lens would help a person with hyperopia?
_____________________________________________________
_____________________________________________________
d) Describe the surgical techniques used on the cornea to correct
myopia or hyperopia.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Exercise 2.4: Cataract
a)
Discuss the social implications of the technology available to
treat cataracts.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 2: Eye can see clearly
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Biology
HSC Course
Stage 6
Communication
Part 3: I can see the light
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20
I
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Contents
Introduction ............................................................................... 2
Photopigments .......................................................................... 4
Photoreceptor cells ..............................................................................5
Nature of photoreceptor cells .............................................................8
The role of rhodopsins in rods ...........................................................10
Colour vision ........................................................................... 12
Seeing colour......................................................................................12
Colour blindness ................................................................................13
Colour communication ......................................................................14
Depth perception ................................................................................17
Summary................................................................................. 21
Suggested answers................................................................. 23
Exercises – Part 3 ................................................................... 25
Part 3: I can see the light
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Introduction
Vision involves the transfer of light energy into electro chemical signals
within the nervous system. These signals or nervous impulses are the
language of the brain and they construct our perception of the
visual world.
Light energy stimulates light sensitive pigments on the retina and
electro chemical signals are carried by nerve fibres to the brain via
the optic nerve.
Photoreceptors in the retina are located in specialised cells called rods
and cones. Both of these cells contain photopigments. Any defect in one
or more of the cone cells will affect colour sensation and causes colour
blindness. Colour blindness results from the lack of one or more of the
colour sensitive pigments. Colour and its perception play a big role in
communication among many different kinds of animals.
In this Part you will be given opportunities to learn to:
2
•
identify photoreceptor cells as those containing light sensitive
pigments and explain that these cells convert light images into
electro chemical signals that the brain can interpret
•
describe the differences in distribution, structure and function of the
photoreceptor cells in the human eye
•
outline the role of rhodopsins in rods
•
identify that there are three types of cones, each containing a
separate pigment sensitive to either blue, red or green light
•
explain that colour blindness in humans results from the lack of one
or more of the colour-sensitive pigments in the cones
•
explain how the production of two different images of a view can
result in depth perception.
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In this Part you will be given opportunities to:
•
process and analyse information from secondary sources to compare
and describe the nature of photoreceptor cells in mammals, insects
and in one other animal
•
process and analyse information from secondary sources to describe
and analyse the use of colour for communication in animals and
relate this to the occurrence of colour vision in animals.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Amended November 2002. The most up-to-date version can be
found on the Board's website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_listb.html
Part 3: I can see the light
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Photopigments
Until the 17th century it was thought the cornea was responsible for the
detection of light. In 1604, the famous astronomer Johannes Kepler
explained in detail how vision works. He said light enters the eye then is
refracted and focused through the lens onto the retina. Kepler identified
the retina as the light sensitive receptor of the eye.
The retina is a thin sheet of cells (0.5 mm thick) that contains
photoreceptor cells. These cells are called rods and cones. They are a
type of modified neurone (nerve cell).
When a vertical section of the retina is examined under a microscope it
is obvious that the retina is a complex structure of many neurones
packed together and contains a number of different nerve cell types.
Ganglion cells (the neurones of the retina taking the message away to the
brain) lie closest to the lens and front of the eye. These are connected
to the bipolar cells which then connect to the photoreceptor cells.
The photoreceptor cells (consisting of rod and cone cells) lie outermost
in the retina against the pigmented epithelium and choroid.
Light must, therefore, travel through the thickness of the retina before
striking and activating the rod and cone cells. Here the light energy is
converted into electro-chemical signals consisting of a stream of sodium
and potassium ions that move across the cell membrane of the neurone.
More about this will be discussed in Part 6 of this module. The optic
nerve contains the ganglion cell axons running to the brain where the
interpretation of the light image is made.
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back of the eye
epithelium cells
rod cells
cone cells
bipolar cells
optic nerve fibre
ganglion cells
optic nerve
light rays
front of the eye
The structure of the retina. Note the direction of the light. Light must pass
through the ganglion and bipolar cells before reaching the light sensitive rod
and cone cells. The electro-chemical signal is sent back through the bipolar
and ganglion cells and on to the optic nerve.
Photoreceptor cells
Photoreceptor cells are responsible for an animal’s perception of vision.
They contain light sensitive pigments that absorb light energy. When the
pigments absorb light they convert the information into an electro
chemical signal that the brain can interpret.
There are two types of light sensitive receptors in the retina of the
human eye.
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∑
Rods are responsible for night vision, and are located in the
peripheral retina.
∑
Cones are responsible for colour vision and fine detail.
They function best under daylight conditions and are mostly
concentrated in a region of the retina called the fovea.
Structure of rods and cones
The diagram below shows the structure of rods and cones. They are
named after their shape. Rod cells are longer and thinner than cone cells
and have a photopigment called rhodopsin. They contain plate-like
membranes containing light-sensitive pigments at one end and a
connection to nerve cells on the other end. Cone cells have a pointed
(cone-shaped) end that contains photopigments called photopsins
arranged in plate-like membranes.
rod cell
cone cell
membranes containing
pigments
mitochodria
nucleus
Structure of rods and cones
Distribution of rods and cones
The photoreceptors are unevenly distributed over the retina. Cones are
concentrated at the fovea, the area of best vision and highest acuity.
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retina
retina
fovea
blind spot
optic nerve
The fovea contains the highest concentration of cone cells. While the rod cells
are scattered over the rest of the retina.
Density (thousands per square mm)
Rods are not present in the fovea and are more concentrated at the sides
of the retina. There are 120 million rods and 6.5 million cones.
200
cone density
150
100
rod density
50
0
–80
–60
–40
rod density
–20
0
20
40
fovea
Angular distance from fovea (degrees)
60
80
The distribution of rod and cone cells across the retina. Note how the number
of cones per square mm drops off rapidly away form the fovea. The rods are
not found at the fovea and also have a decreasing density away form
the fovea.
Function of rods and cones
Rod cells are important in night vision and peripheral (or side) vision.
They are very efficient photoreceptors and respond to low levels of light.
They detect movement and shapes but do not distinguish between
colours. There are more rods than cones and they are more sensitive to
light than the cones. The photosensitive pigment in rods is a form of
rhodopsin that is particularly sensitive to blue-green light (505 nm).
Cones cells are only stimulated by bright light and are important in day
vision, colour vision and acuity of vision. The number of cone cells in
an area decides the visual acuity that is possible. When you are looking
at fine print you position your head so that the image falls directly on the
Part 3: I can see the light
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fovea where most of the cone cells are located. At night it is better to
look out of the side of your eye if you want to see something in dim light.
This forces the image to fall onto an area that has rod cells which are
more sensitive to low light.
Birds such as hawks and eagles have two area of visual acuity (fovea)
and four types of cone cells.
Do Exercise 3.1.
Nature of photoreceptor cells
Seeing has great survival value resulting in the evolution of a variety of
light sensitive cells among animal species. One of the amazing facts
about vision is that rhodopsin is used in all visual systems whether the
organisms are a flatworm or a human.
Simple eyes
Simple eyes (called ocelli) are found in worms (such as the flatworm),
molluscs and crustaceans. Planaria, a type of flatworm, have eyes that
are located in a hollow called a cup eye. These eyes do not detect colour
and only give information on the direction of the light source.
They interpret light signals and turn their bodies so that the minimal
amount of light is falling on their eyes and then swim in that direction
away from the light.
light
photoreceptor cell
nerve fibres
pigment cup
Simple eyes only give directional information. No image is formed.
(Photo: David Stanley)
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Compound eyes
Insects have compound eyes made up of a large number of separate light
receptors called ommatidia. They have three-colour vision including
the ultraviolet range of the spectrum. The eye forms an image.
Each ommatidium has its own cornea and a lens made up of a crystalline
cone. The number of ommatidia varies from only 20 in some crustaceans
to the dragonfly which has more than 28 000. These eyes can have high
flicker speeds for detecting movement; can detect ultraviolet light and the
polarisation of light.
lens
retinal cell
crystalline cone
nerve fibres
to brain
Compound eye of a fly. (Photo: David Stanley)
Single lens eye
Mammals have a more complex camera type of eye found in all
vertebrates and cephalopods. These eyes can focus and form an image.
There are different types of receptors found in the eye. Some are capable
of colour vision while others are important in visual acuity and night
vision. By having two eyes information can be gathered about depth
perception. Each eye has a single lens.
The mammal eye is a single lens eye that produces a colour image although
that colour image may not be seen exactly as humans see it.
(Photo: Jane West © LMP)
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In the following activity you will compare and describe the nature of
photoreceptor cells in the eyes of a mammal, the compound eye of an insect
and in the simple light receptors of a flatworm.
Hint
The information above is a good starting point. You could also look for
information by searching the Internet using search words like ‘animal
vision’. There are also some webpages gathered for you on the LMP
Science Online web site at: http://www.lmpc.edu.au/science
Biology textbooks and popular scientific journals such as New Scientist are
also good secondary sources of information.
A good way to process the information is to summarise the information in a
table. You could use the format given below. When analysing information
you can look for similarities or generalisations that are common to all visual
systems and look for differences such as whether they have colour vision or
form an image.
Group
Examples
Nature of photoreceptor
cells
Vision
flatworm
planaria
rhodopsin located in simple
cup eyes
direction of light
insect
bee
rhodopsin located in
compound eyes that
consist of individual
ommatidia
colour vision, depth
perception,
detection of
movement
mammal
dog, human, cat
rhodopsin, rod and cone
cells
depth perception,
colour vision,
detection of
movement, night
vision
The role of rhodopsin in rods
Rhodopsin is a photosensitive pigment. It consists of two molecules
joined together, they are retinal (a derivative of vitamin A) and opsin.
When light falls on rhodopsin a series of chemical reactions break the
molecule of rhodopsin into retinal and opsin. This generates the
electrical impulse that is transmitted to the bipolar cells, the ganglion
cells and then through the optic nerve where the signal is interpreted by
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the brain. Several milliseconds are required before the absorption of
light can be recorded as electrical activity in the receptor cell membrane.
Opsin and retinal then recombine to form rhodopsin and can then be
split again by light. The reaction is reversible and is known as the
visual cycle.
Rods cells only have a form of rhodopsin often called visual purple.
It responds to light in the blue–green area of the spectrum.
Relative absorbance
rod 498 nm
400
450
500
550
600
Wavelength (nm)
650
700
Absorption spectrum for rhodopsin
Cones have three types of photopigments and will be dealt with in the
next part on colour vision.
Do exercise 3.2
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Colour vision
In 1802 the scientist and medical doctor Thomas Young concluded that
the retina responded to only three principle colours which combined to
form all the other colours in humans. These three colours of light are
red, blue and green.
It is the cone cells that are the photoreceptors responsible for colour
vision. It is now known that cone cells contain three different kinds of
photopigments each sensitive to a different set of colour wavelengths.
Each photopigment has its own form of opsin combined with retinal to
form pigments known as photopsins. These three different
photopigments combine to produce the array of different hues detected
by the human eye.
Seeing colour
There are three types of cone cells:
•
red cones
•
blue cones
•
green cones.
Each type of cone has a different range of light sensitivity but their
sensitivities overlap. When light energy hits the eye, more than one of
the three types of cone cells will be stimulated. The retina and the brain
process the mixture of the stimulation so that different hues and
intensities are perceived, allowing many more colours to be recognised
than the three detected by the cone cells.
The first type of cone cell is called S cones (S for short wavelength
437 nm) or blue cones. These are sensitive to blue and violet light.
Next is the M or green cones (medium wavelength 533 nm) these
respond to green light. The third type is L cone or red cones (long
wavelength 564 nm) these respond to the red end of the spectrum.
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The graph below shows the sensitivity of each type of cone cell.
Notice that they do overlap.
100
green cones
537 nm
red cones
564 nm
Absorbance (%)
blue cones
437 nm
0
350
400
450
500
550
600
Wavelength (nm)
650
700
750
Colour discrimination occurs through the integration of information
arriving from all three types of cones. For example, the perception of
yellow results from a combination of inputs from green and red cones,
and relatively little input from blue cones. If all three cones are
stimulated, white is perceived. If a red light is shone into the eyes then
only the red cones will fire and the colour is perceived as red. If none of
the cones fire the colour is perceived as black.
Do Exercise 3.3.
Colour blindness
Full colour vision depends on having all three types of cone cells being
present and functioning properly. Any defect in one or more of these
cone cells will affect colour sensation and people with this condition are
known as colour blind. The most common form of colour blindness is
red/green colour blindness. People with this condition have trouble
telling the difference between brown, red and green.
Colour blindness is the inability to distinguish certain colours. It occurs
when one or more of the cone types are missing or defective to any
extent. They may be absent entirely or unable to manufacture the
necessary signals to the brain.
Colour blind people may experience no colour sensation or abnormal
colour matching and colour confusions. Colours that look different to
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people with normal colour vision, can look the same to people with
defective colour vision. Grass may appear green to non-colour blind
people, but be the same colour as orange for people with certain colour
defective vision. There is also a reduction in the number of separate
colours that can be distinguished in the spectrum.
Test your own colour vision by looking up the links for this module in the
LMP Science Online web site at: http://www.lmpc.edu.au/science
Do Exercise 3.4 now.
Colour communication
Animals that use colour to communicate include fish, amphibians,
reptiles and birds. Humans and some other primates are among the few
mammals that see colour as you see it.
Animals use colour communication for a variety of reasons including:
•
to signal their availability to mate and other kinds of reproductive
behaviour like courtship
•
to warn off predators
•
protective coloration and camouflage.
If an animal is using colour for communication, to be effective the
receiver must be capable of colour vision. Examples of colour
communication are:
•
camouflage
•
mimicry
•
sexual dimorphism
•
breeding colours
•
warning colours.
Camouflage
Camouflage is hiding by blending into the environment. Some animals
are masters of this and can change the colour of their skin to match
wherever they are. Examples of animals that can do this are chameleons
and the octopus.
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Two chameleons on a stick. The lower one has been there for a while and has
changed colour to match the surroundings. The top chameleon has just
arrived. (Photo: Jane West © LMP)
Mimicry
Many animals that are poisonous advertise this by having striking
colouration. Other animals who are not poisonous have evolved the
same colouration to fool predators into not attacking them. An example
of this is the Monarch butterfly and the Viceroy butterfly. Both have
similar appearance but only the Monarch has a bad taste.
Sexual dimorphism
Sexual dimorphism is different appearance between the sexes. In many
species the males and females can be distinguished by their different
colours or sizes.
The example below shows a male lion. Only the male lion develops
the mane.
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The male lion is sexually dimorphic from the female.
(Photo: Jane West © LMP)
Birds also show dramatic sexual dimorphism. Often the male bird is
brightly coloured while the female is plain coloured.
Warning colours
Some animals change colour to give a warning that they are about to
attack. The blue-ringed octopus is a famous example of this. The small
octopus uses camouflage to hide in rocks but when threatened small
iridescent blue rings appear all over the surface of the skin.
Breeding colours
Many birds take on different colours during the breeding season.
The example below is a male puffin. During the breeding season the
bands on the beak are bright, while outside of the breeding season the
bands fade.
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Male puffin with breeding colours on its beak.
(Photo: Upgrade Business Systems Pty Ltd)
Animals that use colour for communication must be able to send the
message to another organism that can receive the message. This gives a clue
that the species sees in colour. If you look at the examples above you will
see that they are all groups of animals that have colour vision (birds, reptiles,
primates). Find three examples of colour communication in animals and
then relate this communication to colour vision.
There are some useful web sites gathered for you on the LMP Science
Online web site at: http://www.lmpc.edu.au/science
Do Exercise 3.5 to record your answers.
Depth perception
The ability to see depth in our three dimensional world is called
binocular vision or sometimes referred to as stereoscopic vision.
Depth perception results from having forward facing eyes.
This produces an overlap between the view from the left and the view
from the right eye. The images formed by both eyes are sorted in the
brain so that a three dimensional picture is formed.
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angle of field of view
area of depth perception
extent of side vision
Depth perception is achieved by having a field of view overlap.
Activity Field of view overlap
Put a hand over your left eye and note how far to the left your right eye can
see. Then repeat this time using the right eye. See how far to the right your
left eye can see. There is a large overlap between the two fields.
The slightly different angles between the views from each eye gives
depth perception.
Lemur
Human
Field of view overlap in a lemur and a human.
You can make assumptions about the ability of other animals to see depth
by studying the arrangement of their eyes. Animals that have forward
facing eyes are probably able to see depth and the need to judge distance
is important for their survival. Predators have forward facing eyes while
many mammals such as horses and antelopes have eyes on the side of
their heads. This is good for keeping an eye out for predators but,
because the field of view overlap is limited, there is less depth
perception. Horses and cows have a field of view of 350 degrees but only
65 degrees of that is overlap for depth perception.
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monocular vision
monocular vision
binocular vision
Field of view overlap in a herbivore
Humans have the eyes of a predator. Animals that do not have an
overlap of vision have monocular vision. Rock doves can see
300 degrees but only 30 degrees of binocular vision.
Animals like monkeys that jump from tree branch to tree branch need a
very sharp sense of depth perception. Birds of prey would also need
excellent stereoscopic vision to swoop down on their prey at high speeds.
Peregrine falcon has excellent depth perception provided by the forward facing
eyes. (Photo: Jane West © LMP)
Part 3: I can see the light
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The table below shows a list of animals with forward facing eyes. Complete the
table by describing how their perception of depth helps them survive in
their environment.
Animal
Survival value
Gorilla
Cat
Koala
Owl
(Photo: Jane West © LMP)
Check your answers.
Do Exercise 3.6 to complete this part of the module.
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Summary
During this part of the module you should have carried out the
following tasks using secondary information. There were no first-hand
investigations.
Secondary information
•
Process and analyse information from secondary sources to compare
and describe the nature of photoreceptor cells in mammals, insects
and one other animal.
•
Process and analyse information from secondary sources to describe
and analyse the use of colour for communication in animals.
Summary of content
•
The retina is a thin sheet of cells that contains the photoreceptors
rods and cones. These cells contain light sensitive photopigments.
•
The cone cells are most profuse in the central area called the fovea,
they have a cone shaped end and are important in visual acuity and
colour perception. There are three types of cone cells each
containing a different photopigment that is sensitive to either red,
blue or green light.
•
Rod cells are located away from the fovea, they have a rod shaped
end and they are important in vision when the light conditions
are dim.
•
There are four types of photopigments found in the human eye.
Three are found in cone cells and each is sensitive to different
wavelength ranges of the visual spectrum. The fourth is found in rod
cells and is sensitive to blue-green light.
•
Colour blind people have a type of cone cell missing in their retina
so are unable to distinguish between some colours.
•
Depth perception is dependent on a field of view overlap.
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Suggested answers
Depth perception
Animal
Survival value
Monkey
Forward facing eyes with great field of view overlap give good depth
perception important when jumping from tree to tree.
Cat
Predator eyes facing forward important when springing onto prey when
hunting.
Koala
Forward facing eyes with great field of view overlap allows the koala to move
between branches.
Owl
Good depth perception for swooping down onto prey.
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Exercises - Part 3
Exercises 3.1 to 3.6
Name: _________________________________
Exercise 3.1: Photoreceptor cells
a)
Name the two types of photoreceptors found in the human eye.
_____________________________________________________
_____________________________________________________
b) Fill in the table
Features
Rod cells
Cone cells
Draw the
structure
Distribution
Function
Part 3: I can see the light
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Exercise 3.2: Photoreceptor cells continued
a)
What are some of the differences in visual perception between a
simple cup eye in a flatworm, the compound eye of an insect and the
camera type of eye found in mammals?
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
b) Outline the role of rhodopsin in rod cells.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Exercise 3.3: Seeing colour
a)
Describe the difference in sensitivity of the three kinds of
photopigments found in cone cells.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
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Exercise 3.4: Colour blindness
From the syllabus you are asked to:
explain that colour blindness in humans results from the lack of one or
more of the colour-sensitive pigments in the cones.
The verb explain has a specific meaning in the context of the Biology
syllabus. This meaning is:
relate cause and effect; make the relationship between things evident;
provide why and/or how.
The scaffold following sets out to show how to approach a question that
uses the verb explain.
Question
Explain that colour blindness in humans results from the lack of one or
more of the colour-sensitive pigments in the cones.
Method of answering
Step 1 Firstly you need to describe the relationship between colour
blindness and the lack of one or more colour sensitive pigments in
the cones.
Step 2 To do that fill in the tables below showing the cause and
effect between colour blindness (the effect) and lack of one or more
colour-sensitive pigments in the cones (the cause).
Step 3 Next you have to describe why or how one is caused by the other.
That is, why does the lack of a colour-sensitive pigment result in colour
blindness?
Step 4 Now take your answer out of the boxes and write down the same
information in complete sentences.
Part 3: I can see the light
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Cause
Effect
Why?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
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Exercise 3.5: Colour communication
a)
Give three examples of animal communication using colour and then
relate this to the occurrence of colour vision.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Exercise 3.6: Depth perception
a)
How does the production of two images lead to depth perception?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
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b) The mountain goat below has forward facing eyes. Most sheep have
eyes on the side of their heads for good peripheral vision. What
possible survival benefits would forward facing eyes be for the
mountain goat?
(Photo: Jane West © LMP)
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
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Biology
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Contents
Introduction ............................................................................... 2
Sound energy............................................................................ 3
Sound is a useful and versatile form of communication.....................4
Looking at sound ....................................................................... 5
Vibrating objects...................................................................................5
Describing a wave................................................................................7
What’s the pitch?................................................................................10
Making sounds ........................................................................ 14
The human larynx...............................................................................14
Structures used for sound communication by other animals ...........15
Summary................................................................................. 17
Suggested answers................................................................. 19
Exercises – Part 4 ................................................................... 21
Part 4: Making sounds
1
Introduction
Sound is a very important for communication in humans and other
animals. Sound is a form of energy that requires a medium to be
transmitted therefore sound cannot travel in a vacuum. For animals
sound is a useful way of communicating and different structures have
evolved to create and to perceive sound. The human larynx is an
example of this.
In this Part you will be given opportunities to learn to:
•
explain why sound is a useful and versatile form of communication
•
explain that sound is produced by vibrating objects and that the
frequency of the sound is the same as the frequency of the vibration
of the source of the sound
•
outline the structure of the human larynx and the associated
structures that assist the production of sound.
In this Part you will be given opportunities to:
•
plan and perform a first-hand investigation to gather data to identify
the relationship between wavelength, frequency and pitch of a sound
•
gather and process information from secondary sources to outline
and compare some of the structures used by animals other than
humans to produce sound.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Amended November 2002. The most up-to-date version can be
found on the Board’s website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_listb.html
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Sound energy
If you go out into the bush or National Park and listen to all the
sounds you will notice that most of them are animals calling each other.
Whether they are calling for a mate, signaling danger or announcing
a food source, sound is very important for communication among
most animals. Some animals such as bats use sound to ‘see’
their environment.
Animals living in water are very dependent on sound vibrations as water
is a very effective medium for carrying sound energy. Solids like rocks
transmit sound waves well and animals living close to the ground like
snakes can detect vibrations.
Two snakes with most of their bodies in contact with the ground.
(Photo: Jane West © LMP)
Part 4: Making sounds
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Sound is a useful and versatile form
of communication
Sound is one of the most important forms of communication. If you
listen to birds singing there are different sounds to communicate a threat,
willingness to mate and the location of food. Dogs have many different
sounds for communication. If you own a dog you will probably be able
to tell if there is someone coming to the door by the sound your dog
makes. If the dog is in pain it will let you know by whining.
This ability to communicate different messages reaches a peak in humans
where speech is used to communicate a range of emotions and intentions.
Sound can also travel over vast distances. Howler monkeys can be heard
throughout the forest areas where they live and the song of Humpback
whales is heard across oceans.
Sound may also be used to locate organisms. If the sound is loud the
animal is close so changing directions may find the source of the sound.
In summary sound is useful because:
•
a variety of sounds with different meanings can be made by one
organism
•
sound travels over distances through both air and water
•
sound works in dark environments
•
the sender and the receiver do not have to be visible to each other
•
the sound gives information on the location of the sender
•
sound can travel around objects.
Do Exercise 4.1 now.
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Looking at sound
What are the features of sounds that you hear? Sounds can be loud or
soft and they can have a variety of tones. The most important aspect of
sound that you need to understand for this unit of work is the pitch.
You might remember from music that pitch describes how high or low a
sound is. The best way to look at a sound is to describe sound energy as
sound waves.
Vibrating objects
When an object vibrates sound is produced. Sound is a form of energy
that travels through a medium. The medium vibrates as the energy
passes through it.
Vibrations produce compressions (zones where the particles are pushed
together) and rarefactions (zones where the particles are spread apart) in
the material or medium that it passes through. The figure below shows
you a sound vibration moving forward as a series of compressions and
rarefactions. The medium can be a solid, liquid or gas.
compression
rarefaction
one sound wave
A sound vibration traveling forward showing a series of compressions and
rarefactions.
The frequency of sound waves is the same as the frequency of the source
vibrations. The way sound energy travels can be analysed using a model
like the one described below.
Part 4: Making sounds
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Optional activity: Modeling sound
You will need a slinky spring for this demonstration then follow these
instructions.
•
Attach one end to a fixed object (or get someone to hold one end
tightly).
•
Stretch the slinky spring until the coil is under tension.
•
Compress a small bunch of the spring up near your hand. See the
diagram below for details.
•
Let go and observe the pulse of energy traveling through the spring
in a forward direction. You will also notice the way it reflects or
bounces back when it hits the end.
compression
rarefaction
rarefaction
compression
rest
compression
The spring represents the medium through which the sound is traveling.
Do exercise 4.2 now.
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Describing a wave
Another way of describing a wave is by using a diagram such as the one
below. This shows one complete wavelength (rarefaction and
compression). A wavelength is the horizontal length of one cycle
of a wave.
One complete wavelength
Continue this wave on by drawing a wave shape pattern so that you draw in
another complete wavelength on this diagram.
Check your answer.
Other aspects of the shape of a wave are the amplitude, and frequency of
the wave. The amplitude is defined as the height of the wave from a
position of rest to the top of the crest of the wave. The greater the
amplitude the louder the sound.
wavelength
amplitude
Frequency is measured in hertz (Hz). This shows the number of cycles
(complete wavelengths) that pass a given point in one second.
The higher the frequency the higher the pitch of a sound. Pitch is the
perception of frequency.
Part 4: Making sounds
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Making a wave
You may like to try this experiment yourself by using one hand to move a
pen up and down on a sheet of paper while slowly pulling the paper away
from the pen with your other hand. Alternatively, have someone else help
you by pulling the paper as you move the pen up and down.
Repeat the experiment twice making sure you pull the paper away at the
same speed each time. Firstly, model a low sound (pitch) by moving the
pen up and down slowly. Then model a high pitch by moving the pen up
and down quickly.
Compare the two drawings by describing the differences between them.
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
The waveform gives a lot of information about the sound. The amplitude
of the wave is the loudness of the sound. The frequency (the
wavelengths passing a particular point in second) is heard as the pitch of
the wave. We hear sounds as high and low. High frequency waves
produce high pitch and we describe the sound as a high sound.
Low sounds have a low pitch and a low frequency.
A more scientific way of looking at sound is to use an instrument called a
cathode ray oscilloscope (CRO).
Cathode ray oscilloscope
A cathode ray oscilloscope is an instrument that allows you to see a
pictorial representation of a sound wave on a screen.
Sound energy is converted into an electrical signal by a microphone.
The microphone in this activity acts a data collector to produce an
electrical signal. This signal is fed into the CRO input where it produces
a curve on a screen. Here is a picture or trace of a sound made by a
human voice.
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Human voice trace
Notice how it doesn’t look smooth but it does have regularity. This is
because voice is made up of a mixture of waves each having a
different pitch.
If you use an instrument such as a tuning fork that can produce a single
pitch the image produced by the CRO will look more like this.
Sound 1
Now you can analyse these waves better because they are clearer.
Part 4: Making sounds
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What’s the pitch?
The higher the number of waves that pass a point in a second the higher
the pitch of the sound. If you are looking at sound waves of different
pitch and the CRO settings are identical then the higher pitched sound
will have more wavelengths on a trace.
Below is a picture of a higher pitch sound recorded on the same CRO as
the one above with exactly the same settings.
Sound 2. Higher frequency, higher pitch and reduced loudness when
compared to Sound 1.
Record the number of crests of the waves in both traces above.
Sound 1 =
crests
Sound 2 =
crests
Check your answers.
Just by counting the number of waves you will notice that there are more
in this one for the same amount of space.
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The two sounds that produced these traces can be compared in the
table below.
Feature
Sound 1
Sound 2
frequency
less
greater
pitch
lower
higher
amplitude
higher
lower
volume
louder
softer
You are required to perform a first-hand investigation and gather
information to analyse sound wave forms.
You can complete this activity by using a digital oscilloscope program that
you can download from the Internet. To see a site where you can download
a digital oscilloscope program visit the LMP Science Online webpage at:
http://www.lmpc.edu.au/science
If you are able to download a program from the Internet to analyse sound
waves you will need to use a microphone to input the sound signal to
your computer. If you don’t have a microphone use the bud earphones
from a walkman radio plugged into the microphone input on your
computer. The small speaker can act as a microphone.
Explore the waveforms by carrying out the following:
•
speak into the microphone and observe the waveform
•
make a high-pitched sound
•
make a low-pitched sound
•
speak loudly
•
speak softly.
Record the waveforms of each of the above.
If you cannot download a digital oscilloscope then use the diagrams
following to answer the questions below.
Part 4: Making sounds
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The three sound waves below all have the same amplitude. They therefore
would all have the same loudness. They have different wavelengths and
different frequencies. They would therefore have different pitches.
Use your knowledge of waves to describe the sound that you would hear for
each of the three waves below.
Trace 1
2
1
2
1
2
3
4
5
6
7
8
9
2
3
4
5
6
7
8
9
2
3
4
5
6
7
8
9
-1
-2
Trace 2
2
1
2
1
-1
-2
2
Trace 3
1
2
1
-1
-2
Trace 1
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
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Trace 2
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Trace 3
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answers.
Do Exercise 4.3.
Part 4: Making sounds
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Making sounds
To be able to communicate, animals have to be able to produce different
sounds. In humans, sounds are made by a combination of the lungs, the
nasal cavity, the voice box, the lips, the tongue and the hard and
soft palates.
The human larynx
Another name for the voice box is the larynx. It is located in the throat.
If you feel your neck you will notice some hard bumps. These are
cartilage that forms the outer structure of the trachea (windpipe).
The larynx is located towards the top of the trachea.
epiglottis
hyoid bone
thyroid cartilage
or Adam’s apple
vocal ligament
cricoid cartilage
Adam’s apple
tracheal cartilage
larynx
trachea
cartilage
Location of the larynx
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Structure of the larynx
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The larynx is also made up of rings of cartilage. Within the cartilage
there are the vocal cords. As you have already read, sound is the result
of vibrations. Therefore to produce sound it is necessary to produce
vibrations. This function is done by the vocal cords.
As you breathe in and out the vocal cords are open. When you start to
talk the vocal cords close and the air passing through causes them to
vibrate. My changing the shape of the vocal cords and the interaction of
the other organs involved in speech (tongue, mouth, respiratory system)
it is possible to get a vast array of sounds.
open
closed
Open and closed vocal cords
Do Exercise 4.4.
Structures used for sound
communication by other animals
To make sound there has to be a mechanism to produce vibrations in the
surrounding medium. The medium may be air or water. There are four
common methods that animals use to produce sound. These are:
•
vibrating a membrane in a flow of air
•
vibrating a membrane like a drum
•
stridulating
•
hitting or slapping a surface.
Vibrating a membrane in a flow of air
This is the method used by frogs and mammals. The larynx contains the
vocal cords, which vibrate to produce different sounds. Air flows past a
membrane and the frequency of the vibration can be changed by the
muscles that contract and relax the membrane.
Part 4: Making sounds
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Birds have a similar structure called the syrinx. It contains a membrane
that vibrates as air passes. The syrinx is located further down the
respiratory system than the larynx and is located at the junction of the
two bronchi. This means that birds can get their sound from two sources
of air and can sing for long periods of time by alternating between the
two air sources while breathing from the other. Dolphins have a larynx
that does not have vocal cords but it is thought that the whistles that
dolphins make come from the larynx while the clicks come from the
nasal sac. This produces ultrasonic sound that is used for both
communication and navigation.
Vibrating a membrane like a drum
Many insects such as cicadas have a membrane called a tymbal that they
vibrate directly through muscles.
Stridulating
In many organisms there is a stridulatory organ. This consists of a
scraper or small peg that is struck against a file like structure. Pitch is
changed depending on how fast the two structures move against each
other. Examples of animals that have stridulatory organs are crickets,
grasshoppers and ants.
Hitting or slapping a surface
Some animals slap surfaces to give off signals. For example, beavers,
woodpeckers and termites.
As far as sound communication goes there are a variety of structures used by
different animals for the production of sound. Gather and process
information from secondary sources to outline and compare some of the
structures used by animals other humans to produce sound.
Hint
This can be done by using a search engine on the Internet or by visiting a
local library for books and journals. You can also use the information
above. The information can be processed by using a table such as the
one in Exercise 4.5.
Some useful starting points have already been gathered for you on the LMP
Science Online webpage at: http://www.lmpc.edu.au/science
Do Exercise 4.5 to finish this part of the module.
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Summary
During this part of the module you should have carried out the following
first-hand investigation.
First-hand investigation
•
Plan and perform a first-hand investigation to gather data to identify
the relationship between wavelength, frequency and pitch of a
sound.
During this part of the module you should have carried out the following
tasks using secondary information.
Secondary information
•
Gather and process information from secondary sources to outline
and compare some of the structures used by animals other than
humans to produce sound.
Summary of content
Sound is a useful and versatile form of communication.
Vibrating objects produces sound. The frequency of the sound is
the same as the frequency of the vibration of the source of the sound.
In humans the larynx produces sound. Other animals use different
methods to produce sound including stridulating and
vibrating membranes.
Part 4: Making sounds
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Suggested answers
Here are suggested answers for many of the questions from
throughout this part. Your answers should be similar to these answers.
If your answers are very different or if you do not understand an answer,
contact your teacher.
Describing a wave
Making a wave
Moving the pen up and down slowly produces a longer wavelength than
moving the pen quickly up and down.
What’s the pitch?
The first trace had 16 crests while the second had 26 crests.
Trace 1 would have a high pitched sound but equal loudness.
Trace 2 would have a lower pitched sound than Trace 1 but
equal loudness.
Trace 3 would have the lowest of the three sounds but equal loudness.
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Exercises - Part 4
Exercises 4.1 to 4.5
Name: _________________________________
Exercise 4.1: Sound energy
a)
Explain why sound considered to be a useful and versatile form of
communication?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) Identify three examples of how animal use the versatility of sound.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
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Exercise 4.2: Vibrating objects
How are sound waves produced?
What is the relationship between the frequency of a sound and the
frequency of the vibration of the source of the sound?
_________________________________________________________
_________________________________________________________
_________________________________________________________
Exercise 4.3: Describing a wave
Label the diagram to show the wavelength and amplitude of the wave.
Define the following terms:
wavelength
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
pitch
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
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frequency
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
amplitude
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Identify the relationship between pitch and frequency. How does this
relate to wavelength?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Exercise 4.4: The larynx
a)
Name the structures of the human body that are involved in
sound production.
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) Outline the structure of the larynx.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
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Exercise 4.5: Animal sound production
Fill in the table below with the information you have gathered about the
different structures animals use to produce sound. The first one is done
for you.
24
Animal
Method of sound production
Human
Vocal cords within the larynx open and close. This causes the
air to vibrate, which produces different sounds.
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Biology
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Part 5: What’s this ear?
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Contents
Introduction ............................................................................... 2
Detection of vibration................................................................. 4
Insects...................................................................................................4
Fish .......................................................................................................6
Mammals .............................................................................................8
The frequency range ...........................................................................9
The ear ................................................................................... 12
Outer ear.............................................................................................13
Middle ear ...........................................................................................13
Inner ear .............................................................................................15
The role of the Eustachian tube.........................................................17
Sound shadow....................................................................................20
Hearing devices ...................................................................... 21
Hearing aids .......................................................................................21
Cochlear implants...............................................................................22
Summary................................................................................. 25
Suggested answers................................................................. 27
Exercises – Part 5 ................................................................... 29
Part 5: What’s this ear?
1
Introduction
The previous part of the module looked at sound as a very
important form of communication for humans and other animals.
Different methods of creating sound were examined. In this part of the
module the other end of sound communication is looked at, the detection
of sound. The human ear is a complex organ that has a role in balance as
well as hearing. Other organisms may have different methods of
sound detection.
When the ear does not work there are artificial ways of
improving hearing.
In this Part you will be given opportunities to learn to:
2
•
outline and compare the detection of vibrations by insects, fish and
mammals
•
describe the anatomy and function of the human ear, including:
–
pinna
–
tympanic membrane
–
ear ossicles
–
oval window
–
round window
–
cochlea
–
organ of Corti
–
auditory nerve
•
outline the role of the Eustachian tube
•
outline the path of a sound wave through the external, middle and
inner ear and identify the energy transformations that occur
•
describe the relationship between the distribution of hair cells in the
organ of Corti and the detection of sounds of different frequencies
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•
outline the role of the sound shadow cast by the head in the location
of sound.
In this Part you will be given opportunities to:
•
gather, process and analyse information from secondary sources on
the structure of a mammalian ear to relate structures to functions
•
process information from secondary sources to outline the range of
frequencies detected by humans as sound and compare this range
with two other mammals, discussing possible reasons for the
differences identified
•
process information from secondary sources to evaluate a hearing
aid and a cochlear implant in terms of:
–
the position and type of energy transfer occurring
–
conditions under which the technology will assist hearing
–
limitations of each technology.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Amended November 2002. The most up-to-date version can be
found on the Board’s website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_listb.html
Part 5: What’s this ear?
3
Detection of vibration
Sound waves are vibrations of molecules. Humans and other mammals
have ears as receptors for sound vibrations. Other organisms use a
variety of structures to detect vibrations. Regardless of the structure
hearing is dependent on mechanoreceptors. These are usually hair cells
in a fluid.
Insects
In Australia you are used to the sound of insects throughout the summer.
The song of cicadas, crickets and grasshoppers may reach such a
level of sound that it is difficult to hear conversations comfortably.
Or sometimes it is only when the sound stops that you hear it.
These sounds are communicating information and for this to occur
insects have developed different organs of sound detection.
Unlike mammals, which have easily identified ears, insects have hearing
organs in many different parts of their bodies. The illustration below is a
composite of different hearing organs and their locations in insects.
The location of sound detection organs found in insects.
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Three of the main types of sound detection organs in insects are:
•
tympanic organs
•
auditory hairs
•
vibration receptor.
Tympanic organs
The tympanic organ consists of a membrane stretched across an air sac.
In grasshoppers, the tympanic organs are located on the legs. This organ
works in a similar way to the mammalian ear. When sound waves reach
the tympanic organ the membrane vibrates and this stimulates the hair
cells attached to the inside of the membrane and a message is sent via a
nerve to the brain. These insects move their legs to pick up the most
intense signal.
Insect with tympanic organ on leg. (Photo: David Stanley)
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Auditory hairs
Many insects are covered in auditory hairs that are sensitive to sound
waves. These have different lengths and stiffness and respond to
vibrations at different frequencies. The hairs are connected to nerve cells
and are particularly abundant on the antennae and legs. Mosquitoes have
auditory hairs on their antennae. Male mosquito can detect female
mosquitoes by the buzz of their wings using these hairs. A tuning fork
with the same frequency as the buzz of female mosquitoes will attract
male mosquitoes.
Vibration receptor
Insects that fly at night have adaptations that can detect ultrasonic sound
produced by bats. Hawk moths hear the ultrasonic sound of bats through
two sets of modified mouthparts. One set of mouthparts form an airfilled chamber while the other is a brush-like organ. These organs detect
ultrasound at the same frequency as the bats that prey upon them.
Give three examples of sound perception organs in insects. What do all of
these organs have in common?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answers.
Fish
Before the invention of sonar and hydrophones to listen to sound
underwater, it was thought that the depth of the ocean was a quiet place.
Looking around at fish there were no visible ears to be seen.
However, nothing could be further form the truth as there is large range
of underwater sounds that are beyond the hearing frequency of humans.
With all this sound going on where were the sound perception organs on
aquatic animals?
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Fish have several different organs to detect sound waves. These include:
•
internal ears
•
lateral line organ
•
swim bladder amplification.
Internal ears
Fish have an ear but unlike mammals they do not have an external
opening or an eardrum. This adaptation relates to physical properties of
sound waves. Sound travels about four times faster in water than air and
the soft tissue of fish has the same acoustic properties as water.
Therefore the sound travels directly through the soft tissues of the fish
without needing an external opening.
Once the sound reaches the internal ear there are two structures. One is
involved in balance (labyrinth) the other containing otoliths is involved
in sound perception. Otoliths and the labyrinth make up the inner ear of
fish. Otoliths are made from calcium salts and are suspended over a
gelatinous membrane that is covered in sensory hair cells. Otoliths are a
different density to the rest of the fish tissue so they vibrate more slowly
than the rest of the tissues as sound waves pass through the fish.
The movement of the otolith across sensory hair cells is interpreted as
sound by the fish.
Lateral line
Along the body of fish and extending over the head is a visible line called
the lateral line. This line is capable of sensing low frequency vibrations
in water. It consists of fluid-filled canals below the surface of the skin
with tiny pores that are open to the exterior.
Fish with lateral line organ. (Photo: Jane West)
Within the fluid-filled canals are collections of sensory hairs
(mechanoreceptors) called neuromasts. These respond to low frequency
sound. The neuromast consists of hair cells covered with a gel-like
Part 5: What’s this ear?
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cupula. When there is movement in the fluid in the lateral line the cupula
is moved and this stimulates the hair cell to fire off an impulse along the
attached nerve to the brain.
The swim bladder
The swim bladder is an organ in fish that is primarily responsible for
equalising pressure between the surrounding water and the fish. It is an
extendable air sac. A fish swimming uses the swim bladder to maintain
buoyancy. In some fish there is a close association between the swim
bladder and the internal ear. The swim bladder acts as an amplifier to
any sound, passing the vibrations directly onto the inner ear.
In some fish such as catfish and goldfish, there are a series of four small
bones (Weberian apparatus) that connect the swim bladder directly to the
inner ear. Hair cells in the inner ear detect the sound.
Give three examples of sound perception organs in fish. What do all of
these organs have in common?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answers.
Mammals
Mammals have ears to detect sound. These ears are located either side of
the head allowing directional information to be acquired. Sound enters
the ear, and travels along the auditory canal. It then causes the tympanic
membrane to vibrate at the same frequency as the sound waves. In the
middle ear the ossicles (small bones) transfer and amplify the sound
vibrations to the oval window. The oval window transfers the sound
vibrations to the fluid-filled cochlea. Inside the cochlea is the organ of
Corti. This has rows of hair cells that respond to different frequencies
and transfer the message to brain via the auditory nerve.
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All of the organisms above have specialised hair cells that act as
mechanoreceptors for sound waves. The difference is in the type and
location of the organ of hearing.
Do Exercise 5.1 now.
The frequency range
Different organisms have the ability to hear a range of sound
frequencies. For example, some fish have a small frequency range from
2 to 500 Hz. Other animals such as whales and dolphins have
frequency ranges that go from 10 to 100 000 Hz. Dogs hear between
60 to 45 000 Hz.
Establishing hearing frequency ranges in animals is very difficult.
It often means that the animal has to be trained to respond to a signal as
animals are not capable of directly reporting if they hear a sound.
The table below gives the approximate frequency ranges of some
mammals hearing.
Animal
Frequency range (Hz)
human
20–25 000
dog
67–45 000
cat
45–64 000
bat
2 000–110 000
Beluga whale
1 000–123 000
elephant
16–44 000
dolphin
75–150 000
mouse
1 000–91 000
rat
200–76 000
If you go to different sources you will find differences to these frequency
range. Even within a species different individuals have different ranges,
for example some breeds of dogs have different hearing ranges.
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Human frequency range
Humans can hear in the range 20 to 20 000 Hz. Younger children can
hear frequencies up to 25 000 Hz but this ability decreases with age.
A typical male about 40–years of age can hear sounds up to about
17 000–18 000 Hz.
Bat frequency range
If you have ventured out at night you may have heard the high-pitched
squeaks of bats. As well as these noises, bats flying around at night are
emitting sound that is well above the human ability to hear. Bats emit
high frequency sound that they use to navigate in the dark. Solid objects
reflect the sound waves back and these are detected by the specialised
ears of the bats.
Bats produce sound in 2 000 to 110 000 Hz range through their mouths
or through elaborate nose organs. The insect-catching bats use
echolocation to locate their prey in mid air. To do this they send out
high frequency sound (ultrasonic) and then interpret the echo that
bounces back. This gives them information on the distance and the
direction of movement.
Whale frequency range
Whales, dolphins and porpoises belong to a group of aquatic mammals
known as cetaceans. They are further divided into toothed whales
(eg. dolphins, Orcas) and baleen whales (eg. Humpbacks, Blue whales).
Toothed whales have a very high frequency hearing range while baleen
whales have very low frequency hearing. Both of these groups have
specialised inner ears. They have more nerve endings than terrestrial
animals with toothed whales having more than baleen whales.
There are differences in the thickness of the basilar membrane in the
inner ear. A thicker membrane is an adaptation for high frequency
sounds. Toothed whales have adaptations for very high frequency sound
detection such as a thick basilar membrane and bony supports for the
cochlea. Baleen whales have a very elastic basilar membrane. This is an
adaptation for low frequency sound detection.
To hear some animal sounds visit the LMP Science Online webpage for this
module at: http://www.lmpc.edu.au/science
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Reasons for different ranges
Sound becomes important in environments where visual information is
limited. It plays an important role in finding mates, prey and avoiding
predators. Bats use sound to navigate in dark environments to avoid
objects and to locate prey. They use high frequency sound which is only
useful over short distances. Humpback whale songs can be heard from
100 kilometres away. This helps to keep the groups in contact and to
locate other members of the species for mating. The frequency of
Humpback hearing is in the low frequency range to be able to detect the
sound of other whales. Other groups of toothed whales such as dolphins
have high frequency hearing. High frequency sound is used over short
distances to locate prey.
Process information from secondary sources to outline the range of
frequencies detected by humans as sound and compare this range with two
other mammals, discussing possible reasons for the differences identified.
Hint
The information above is useful and there are some good starting points on
the LMP Science Online webpage at: http://www.lmpc.edu.au/science
A good way to process the information is to use a graph to display the
information from a hearing frequency table. Go to Exercise 5.2 to carry out
this activity.
Part 5: What’s this ear?
11
The ear
You may have been to the doctor with an ear problem and have been
told that you have a middle ear infection. What does that mean?
Knowing the structure and function of the ear will help to answer
this question.
The human ear is an organ that has two functions, balance and the
detection of sound. In this part of the module the detection of sound will
be discussed.
The ear can be divided into three sections:
•
the outer ear
•
the middle ear
•
the inner ear.
Find these three areas in the diagram below.
outer ear
middle
ear
inner ear
The three major areas of the ear
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Outer ear
The outer ear is the part that you can see from the outside and by looking
into the ear canal. It starts at the external ear and ends at the eardrum.
Anatomy
The outer ear consists of the fleshy organs located on the side of
your head that you call your ears, the ear canal and the eardrum.
The scientific names for these parts are pinna (external part of the ear)
auditory canal (ear canal) and tympanic membrane (eardrum).
Locate these structures on the diagram below.
outer ear
tympanic
membrane
(eardrum)
pinna
auditory
canal
Structures of the outer ear.
Function
The pinna collects sound waves and channels the sound into the ear.
From here the vibrations travel along the auditory canal until they reach
the eardrum. Here they cause the tympanic membrane to vibrate at the
same frequency as the incoming sound waves. The sound waves in air
have been changed into vibrations in a solid (the tympanic membrane).
Middle ear
The middle ear is an air-filled chamber that contains the ear ossicles and
the Eustachian tube. It lies between the eardrum and the oval window.
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Anatomy
The ear ossicles are three tiny bones that are found in the middle ear.
They are named after their shapes. You may recall the names hammer,
anvil and stirrup. The scientific names for these bones are the malleus
(hammer), incus (anvil) and stapes (stirrup). The stapes is the smallest
bone in the human body. Also in the middle ear is the Eustachian tube,
which has a role that will be discussed later. Locate these structures on
the diagram below.
tympanic
membrane
middle
ear
stapes
malleus
incus
Eustachian tube
Structures of the middle ear.
Function
The function of the middle ear is to transmit and amplify the vibrations
from the outer ear to the inner ear. The first of the ossicles, the hammer
is attached to the tympanic membrane and vibrates at the same frequency
as the vibrating tympanic membrane. The vibrations then pass through to
the anvil and the stirrup. These tiny bones act as levers and magnify the
vibrations by up to twenty-two times. The stirrup is attached to the oval
window, which lies between the middle and the inner ear. As the stirrup
pushes against the oval window the vibrations are transmitted through to
the fluid in the inner ear.
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incus
malleus
connects to the
oval window of
the cochlea
stapes
tympanic membrane
(eardrum)
The three ossicles of the middle ear, malleus, incus and stapes.
Inner ear
The inner ear is located within the bone of the skull. It consists of fluid
filled chambers called the semicircular canals and the cochlea. It extends
from the oval window to the auditory nerve.
Anatomy
The oval window is a membrane that separates the middle and inner ear.
The fluid filled inner ear contains the semicircular canals and the
cochlea. The semicircular canals are involved in balance. The cochlea is
the sense organ of hearing. It is a spiral tube, about the size of a pea, and
similar in shape to a snail’s shell (thus the name which means snail). It is
divided into three parts, which are separated by two membranes.
Find these structures on the diagram below.
inner ear
semicircular canals
auditory nerve
cochlea
oval window
round window
Structure of inner ear.
Within the cochlea is the organ of Corti. The organ of Corti has hair
cells located on the basilar membrane. These hair cells have cilia that are
in touch with another membrane called the tectorial membrane.
Part 5: What’s this ear?
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Function
As the vibrations from the stirrup push on the membrane of the oval
window the vibrations are transferred into waves in the liquid filled
chambers of the cochlea. The round window allows the liquid in the
cochlea to bulge outwards allowing movement in the fluid within the
cochlea. Depending on the frequency and amplitude of the sound
different receptors (hair cells) within the organ of Corti are stimulated
and fire a nerve impulse that travels along the auditory nerve to be
interpreted by the brain. The hair cells in the organ of Corti transduce
(transfer energy from one medium to another) the energy of vibrating
fluids into action potentials in the nerves.
semicircular canals
auditory nerve
oval window
round window
cochlea
The inner ear
Gather, process and analyse information for secondary sources on the
structure of a mammalian ear to relate structures to functions.
Hint
To do this use a search engine to look for the structure and function of
the human ear on the Internet. Use search terms such as ‘human
ear+structure’. Another good source of information would be Biology
textbooks. Use the index to find the correct page. Or use the information
given above.
Analyse the information by relating structure to function. For example,
the auditory nerve links the ear with the brain therefore allowing the
transmission of signals between the two organs. The tympanic
membrane is a thin membrane stretched across the ear canal.
Its flexibility allows it to vibrate when sound waves enter the ear.
The pinna is shaped so that it picks up sound waves but blocks sounds
that are coming from behind the head. This allows the direction of
sound to be determined.
Process the information by completing the table in Exercise 5.3.
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The role of the Eustachian tube
You may have had the experience of your ears ‘popping’ when you go up
a mountain or dive to the bottom of a swimming pool. This is caused by
rapid air pressure adjustment in the Eustachian tube. The Eustachian
tube connects the middle ear with the back of the throat. It is filled with
air and responds to changes in pressure. The role of the Eustachian tubes
is to keep the pressure in the middle ear and the throat and therefore the
outside atmosphere equal and to drain the middle ear. It also replaces the
air in the middle ear after it has been absorbed.
From your understanding of the structure of the ear you should now have
a better understanding of where a middle ear infection would occur and
how bacteria could gain access into the middle ear.
Do Exercise 5.4 looking at the role of the Eustachian tube.
The organ of Corti
The organ of Corti detects the different frequencies or pitch of sound.
This is achieved by the sensory hair cells that are arranged in parallel
rows along the basilar membrane. This membrane is about 2.4 cm long
and lies coiled within the cochlea. There are more than 15 000 hair cells
in the organ of Corti. Different hair cells respond to different frequencies
of sound. Each hair cell has stereocilia which look like tiny hairs (thus
the name hair cells) attached at the end.
Rows of hair cells in the organ of Corti.
The last of the ossicles (stapes) causes the oval window to vibrate and
this sends pressure waves into the fluid in the cochlea. Pitch is a function
of the wave frequency of sound waves. It is recognised in the organ of
Corti because the basilar membrane is not uniform along its length. It is
thicker and less flexible at the start of the organ of Corti and narrow and
more flexible at the other end of the membrane. Different frequencies
bend the basilar membrane along it length. When a region of the basilar
Part 5: What’s this ear?
17
membrane is stimulated by a particular frequency of sound the basilar
membrane moves upwards (flexes) and the stereocilia then contact the
tectorial membrane. High frequency sound waves flex the membrane a
short distance along the membrane while low frequency sounds travels
further into the cochlea. The volume of the sound (amplitude of the
sound waves) increases the number of hair cells that are bent and results
in more nerve impulses to the brain.
The stereocilia that responds fires off a message to the brain.
The combination of hair cells that fire gives information about the
frequency, intensity and length of the sound wave and is then
interpreted to be a particular sound.
tectorial membrane
stereocilia
hair cell
basilar membrane
The organ of Corti
Do Exercise 5.5 now.
Path of sound
Sound enters the ear at the pinna as energy in the form of sound waves in
a gas. When the sound waves reach the tympanic membrane the energy
is changed into vibrations in a solid. The energy is then transferred and
amplified by the ossicles in the inner ear. At the oval window the energy
is transferred to vibrations in a fluid in the cochlea of the inner ear.
Here the energy is transduced into electro chemical energy by the
stereocilia of the hair cells. The stereocilia are attached to neurones.
The axons of the neurones join together to form the auditory nerve.
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outer ear
sound energy
middle ear
mechanical energy
inner ear
electro-chemical energy
Energy transformations in the ear
Trace the path of sound through the ear by using the following words to fill
in the blanks below.
cochlea, middle, tympanic, ossicles, hair, malleus, pinna, incus, stapes,
organ of Corti, auditory
When sound waves enter the_____________ they travel along the
auditory canal and cause the ___________________ membrane
(eardrum) to vibrate. These vibrations are carried and amplified by the
_____________in the____________ ear. The ossicles are three tiny
bones also known as the ______________ (hammer), the
_________________ (the anvil) and the ____________ (the stirrup).
The ossicles join the inner ear at the oval window. The ____________ is
a snail-shaped, fluid-filled structure in the inner ear. Inside the cochlea is
another structure called the ________________________. Inside the
organ of Corti there are _________ cells located on the basilar
membrane. These are in contact with the tectorial membrane. When
vibrations reach the hair cell the message is converted into an electrochemical response which travels via the ____________nerve to the brain.
Check your answers.
Do Exercise 5.6.
Part 5: What’s this ear?
19
Sound shadow
When a human hears a sound there is information about the direction of
the sound. This comes from the location of the ears on either side of the
head. If the volume of the sound is the same then the sound is coming
from straight ahead. If it is to the left then the stimulus reaching the left
ear will be greater than the stimulus that arrives at the right ear.
There will also be a slight time delay. This is because the head forms a
sound shadow.
sound source
sound shadow
The sound shadow
The sound waves have to travel around the head to the opposite ear.
The brain interprets the difference between the waves arriving at each ear
and the direction of sound is then known. When you hear a sound you
usually turn your head so that the sound is equal in both ears at that point
you will looking in the direction of the source of the sound.
Do Exercise 5.7.
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Hearing devices
When hearing is not working efficiently there are some devices that can
improve or return hearing. Two of these devices are:
•
hearing aids
•
cochlear implants.
Hearing aids
Hearing aids are small electrical devices that sit behind the ear.
They consist of a microphone, an amplifier, a receiver and a speaker.
The hearing aid takes sound waves arriving at the ear, increases the
volume and redirects the sound into the ear.
Position and type of energy transfer
occurring
Hearing aids detect sound waves. The energy is then transferred to
electrical energy which is then transformed back into sound waves which
are amplified into the auditory canal.
Conditions under which the technology will
assist hearing
Hearing aids are useful when there has been damage to the outer and
middle ear. They will not improve hearing if there has been damage to
the inner ear. The technology is much cheaper than the cochlear implant
and does not have the risks associated with surgical treatments.
Part 5: What’s this ear?
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Limitations of technology
Hearing aids are amplifiers, making the sounds in the environment
louder. Louder does not necessarily lead to better hearing. Hearing aids
are a simple device that are relatively cheap but some people find them
annoying as they amplify all sound including background noise.
Cochlear implants
Cochlear implants are also known as the bionic ear. This is an Australian
invention by Dr Graeme Clark. They consist of external parts and
surgically implanted parts. They return a sense of hearing to people who
have damaged middle or inner ear function.
Position and type of energy transfer
occurring
The external parts include a microphone, speech processor and a
transmitter. The microphone picks up sound waves and sends them
to the speech processor. This is usually located behind the ear or in
a pocket.
Sound waves are picked up by the microphone and are processed by the
speech processor into an electrical signal. The speech processor is a
computer that digitises the sound. This signal is then sent to the
transmitter coil located on the outside of the ear. FM radio waves
transfer the signal to the implanted receiver. This then transmits the
signals to the electrodes inside the cochlea which is interpreted by the
brain. The electrodes stimulate the nerve fibres in the auditory nerve.
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microphone
hook over ear
implant receives radio
waves (and sends signals
through electrode)
electrode stimulates nerve
endings inside cochlea
speech
processor
ear drum
transmitting coil (sends FM radio
waves through skin to implant)
The cochlear implant
Conditions under which the technology will
assist hearing
Cochlear implants are particularly useful to people who have sustained
middle ear damage or damage to the hair cells in the middle ear.
These people would not benefit from traditional hearing aids.
The cochlear implant directly stimulates the auditory nerve therefore bypassing the hair cells.
Limitations of technology
The cochlear implant does not help all people with hearing difficulties.
It has some limitations including:
•
it is different from hearing sound
•
it requires the person to learn to interpret the sensations they receive
•
it takes time and experience for this to occur.
There are also risks associated with the surgery that requires a
general anaesthetic including risks to the facial nerves and the chance
of infection.
Part 5: What’s this ear?
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Process information from secondary sources to evaluate a hearing aid and a
cochlear implant in terms of:
–
the position and type of energy transfer occurring
–
conditions under which the technology will assist hearing
–
limitations of each technology.
Hint
Use Biology textbooks, CD ROMs or the Internet to search for information
on hearing aids and the cochlear implants. There are some useful sites
gathered for you on the LMP Science online webpage for this module at:
http://www.lmpc.edu.au/science
The information above would also be useful.
Use the table in Exercise 5.8 to process the information from secondary
sources on technologies that assist hearing.
This completes Part 5 of Communication.
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Summary
There were no first-hand investigations in this part of the module.
However, during this part of the module you should have carried out the
following three tasks using secondary information.
Secondary information
•
Gather, process and analyse information from secondary sources on
the structure of a mammalian ear to relate structures to functions.
•
Process information from secondary sources to outline the range of
frequencies detected by humans as sound and compare this range
with two other mammals, discussing possible reasons for the
differences identified.
•
Process information from secondary sources to evaluate a hearing
aid and a cochlear implant in terms of:
–
the position and type of energy transfer occurring
–
conditions under which the technology will assist hearing
–
imitations of each technology.
Summary
•
Organisms have different ranges of frequency in their hearing.
•
Hair cells are the sense organs that detect sound in animals but these
are found in different types of organs.
•
The structure of the mammalian ear is related to the function of
hearing and balance.
•
The Eustachian tube equalises the air pressure between the ear and
the back of the throat.
•
Sound waves arrive at the ear and are changed to vibrations in the
tympanic membrane. The ossicles transfer these vibrations to the
cochlea via the oval window. The hair cells in the organ of Corti
Part 5: What’s this ear?
25
respond to specific frequencies. This information is changed into
electro chemical impulses which travel via the auditory nerve to the
brain where the sound is interpreted.
26
•
The sound shadow cast by the head assists in the location of sound
by comparing the different signals that arrive at each ear.
•
When there are hearing difficulties some devices such as hearing
aids and the cochlear implant may be useful to restore hearing.
Each of these has specific uses and limitations.
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Suggested answers
Here are suggested answers for many of the questions from
throughout this part. Your answers should be similar to these answers.
If your answers are very different or if you do not understand an answer,
contact your teacher.
Insects
Examples of sound perception organs in insects are tympanic organs,
auditory hairs and modified mouthparts. All of these organs have
sensory hairs.
Fish
Examples of sound perception organs in fish are internal ears, lateral line
organ and swim bladder amplification. In all cases it is sensory hairs that
are associated with the perception of sound.
Fill in the blanks
When sound waves enter the pinna they travel along the auditory canal
and cause the tympanic membrane (eardrum) to vibrate. These vibrations
are carried and amplified by the ossicles in the middle ear. The ossicles
are three tiny bones also known as the malleus (hammer), the incus (the
anvil) and the stapes (the stirrup). The ossicles join the inner ear at the
oval window. The cochlea is a snail-shaped, fluid-filled structure in the
inner ear. Inside the cochlea is another structure called the organ of
Corti. Inside the organ of Corti there are hair cells located on the
basilar membrane. These are in contact with the tectorial membrane.
When vibrations reach the hair cell the message is converted into an
electro chemical response which travels via the auditory nerve to
the brain.
Part 5: What’s this ear?
27
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Exercises - Part 5
Exercises 5.1 to 5.8
Name: _________________________________
Exercise 5.1: Detection of vibration
a)
Outline the detection of vibrations by insects, fish and mammals.
Insects _______________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Fish _________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 5: What’s this ear?
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Mammals _____________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Compare has a specific meaning for your Biology course. It is
defined as ‘show how things are similar and different’. To answer
this question describe how the detection of vibrations by insects, fish
and mammals are similar and how they are different.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Exercise 5.2: Frequency of hearing
a)
30
Use the table and graph paper below to graph the hearing
frequencies of a range of organisms. You may choose to use a
spreadsheet program if you have access to one.
Animal
Frequency range (Hz)
human
20–25 000
dog
67–45 000
cat
45–64 000
bat
2 000–110 000
Beluga whale
1 000–123 000
elephant
16–44 000
dolphin
75–150 000
mouse
1 000–91 000
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b) Name two of the organism above and compare the frequency range
with that of humans. What possible reasons can you suggest for the
differences observed?
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Part 5: What’s this ear?
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______________________________________________________
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______________________________________________________
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______________________________________________________
Exercise 5.3: The ear
a)
32
On the diagram below label the following structures: the outer,
middle and inner ear, pinna, tympanic membrane, ear ossicles, oval
window, round window, Eustachian tube, cochlea, auditory canal,
auditory nerve.
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b) Fill in the table outlining the anatomy and function of structures of
the ear.
Structure
Anatomy
Function
pinna
tympanic membrane
ear ossicles
oval window
round window
cochlea
organ of Corti
auditory nerve
Part 5: What’s this ear?
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c)
Choose three of the structures above and describe how the structure
is related to the function.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Exercise 5.4: The role of the Eustachian tube
Outline the role of the Eustachian tube.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Exercise 5.5: The organ of Corti
Describe the relationship between the distribution of hair cells in the
organ of Corti and the detection of sounds of different frequencies.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
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_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Exercise 5.6: Path of sound
Trace the path of a sound wave through the external, middle and inner
ear and identify the energy transformations that occur.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Exercise 5.7: The sound shadow
a)
What is the sound shadow?
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) Outline the role of the sound shadow cast by the head in the location
of sound.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
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Exercise 5.8: Hearing devices
a)
Fill in the table below to illustrate the differences between hearing
aids and the cochlear implant.
Feature
Hearing aid
Cochlear implant
energy transfer
type of hearing loss
limitations
advantages
b) Evaluate the two devices in terms of:
i)
the position and type of energy transfer occurring
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
ii) conditions under which the technology will assist hearing
__________________________________________________
__________________________________________________
__________________________________________________
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iii) limitations of each technology
_________________________________________________
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Part 5: What’s this ear?
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Biology
HSC Course
Stage 6
Communication
Part 6: It’s all in the head
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Contents
Introduction ............................................................................... 2
The nervous system .................................................................. 3
The neurone .........................................................................................3
The nerve impulse................................................................................8
The brain ................................................................................. 11
Cerebrum............................................................................................11
Cerebellum .........................................................................................13
Medulla oblongata..............................................................................14
Dissection of a sheep’s brain.............................................................14
Looking at a model brain....................................................................20
Interpretation of sensory signals ......................................................22
Summary................................................................................. 25
Suggested answers................................................................. 27
Exercises – Part 6 ................................................................... 29
Part 6: It’s all in the head
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Introduction
Once stimuli have been detected it is the function of the nervous system
to transfer the information as electro chemical signals to the relevant
parts of the brain for interpretation. There is some practical work to do
in this part. You will need a cutting board, a sheep’s brain, a scalpel or
knife and newspaper. Alternative exercises are provided.
In this Part you will be given opportunities to learn to:
•
identify that a nerve is a bundle of neuronal fibres
•
identify neurones as nerve cells that are the transmitters of signals by
electro chemical changes in their membranes
•
define the term threshold and explain why not all stimuli generate an
action potential
•
identify those areas of the cerebrum involved in the perception and
interpretation of light and sound
•
explain, using specific examples, the importance of correct
interpretation of sensory signals by the brain for the coordination of
animal behaviour.
In this Part you will be given opportunities to:
•
perform a first-hand investigation using stained prepared slides
and/or electron micrographs to gather information about the structure
of neurones and nerves
•
perform a first-hand investigation to examine an appropriate mammalian
brain or model of a human brain to gather information to distinguish the
cerebrum, cerebellum and medulla oblongata and locate the regions
involved in speech, sight and sound perception
•
present information from secondary sources to graphically represent
a typical action potential.
Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Amended November 2002. The most up-to-date version can be
found on the Board’s websites at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_listb.html
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The nervous system
For the perception of information to be used there must be a rapid system
of communication within the body of an organism. This task is achieved
by the nervous system. The nervous system consists of a coordinating
organ, the brain and a system of branching nerves that reach to all parts
of the body. The basic structure of the nervous system is the neurone
(neuron) or nerve cell. Neurones receive the signals from the sense
organs and transmit the information by electro chemical changes in their
membranes. A bundle of neuronal fibres are known as a nerve.
Nerves connect to the central nervous system (CNS) that consists of the
brain and the spinal cord. The transfer of a stimulus from the body
extremities to the brain takes only milliseconds to occur.
The neurone
Neurones are nerve cells that transmit signals by electro chemical
changes in their membranes. They consist of a cell body containing a
nucleus, cytoplasm and organelles, and extensions or processes to either
end called dendrites and axons.
The neurone transmits the electro chemical signal in one direction only.
The axons conduct the signal away from the cell body (an easy way to
remember is away and axon both start with the letter a). The dendrites
take the signal to the cell body.
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direction of impulse
synaptic terminals release
neurotransmitters into the synapse
cell body
dendrites
nucleus
myelin sheath
axon
A neurone
Axons
Many neurones only have one axon. Axons are branched at the
end leading to many synaptic terminals. These release the
neurotransmitters into the gap between neurones called the synapse.
Some axons have a fatty insulating material known as the myelin sheath
wrapped around the axon. This is part of some specialised cells known
as Schwann cells. Axons may be more than a metre in length, for
example in the sciatic nerve, although some in the brain are less
than a millimetre. At the end of the axons are sacs that contain
the neurotransmitters.
Dendrites
Dendrites are small branch-like projections that connect to other cells.
The branching nature increases the available surface area and allows
connection for incoming impulses. Dendrites can grow and shrink
during the life of the neurone. Alcohol and old age has been shown to
reduce dendrites while a situation where the person is learning can
increase the growth of dendrites. Dendrites are shorter and thinner than
the axon.
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Types of neurones
There are many different types of neurones but they can be grouped into
three major categories:
•
sensory
•
motor
•
connecting.
Sensory neurones have the dendrites attached to a sensory organ such as
the ear. They change the information form the stimulus such as sound
into an electro chemical response in the neurone. Sensory neurones have
their axons attached to another neurone.
Motor neurones are in a way the opposite of sensory neurones.
They have their dendrites connected to other neurones but their axons are
connected to effector organs such as muscles and glands.
Connecting neurons (interneurones) have both their axons and dendrites
attached to other neurones. They are most common in the spinal cord
and brain.
The synapse
Between each neurone is a small gap called a synapse. For an impulse to
cross the synapse neurotransmitters are released by the axon terminals.
Common neurotransmitters are dopamine, histamine and endorphin.
When these chemicals reach the dendrites of the next cell it causes the
next neurone to fire. This explains why the signal in neurones is
known as an electro chemical response. Along the neurone the signal
is electrical while at the synapse the signal is changed into a
chemical signal.
The effects of many drugs such as depressants and stimulants affect the
transmission of nerve impulses across the synapses of nerve cells by
suppressing or increasing the release of neurotransmitters.
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direction of signals
synapse
axon terminal
axon
dendrite of
next neurone
neurotransmitters
The synapse between two neurones
Nerves
Nerves are bundles of nerve fibres (that is dendrites or axons) outside of
the brain. The fibres are surrounded by myelin which acts as an
insulator. You have already learnt about the auditory nerve and the optic
nerve when studying the ear and the eye. These are the collective axons
coming from the hair cells in the cochlea or the rod and cone cells in
the eye.
blood vessel
nerve
axon
connective tissue
A nerve bundle is made up of neuronal fibres.
Do Exercise 6.1 now.
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Microscopic examination of neurones
Perform a first-hand investigation using stained prepared slides and/or
electron micrographs to gather information about the structure of neurones
and nerves.
If you do not access to a microscope and slides there are some micrographs
on the LMP Science Online websites at: http://www.lmpc.edu.au/science
There are also some links to pages on the Internet that have more
micrographs including electron micrographs. Below is a micrograph of
some neurones as seen under a light microscope. The clearest feature in the
picture is the large cell bodies with the darker stained nucleus.
neurone
nucleus
cell body
Light micrograph of nerve cells. (Photo: J West)
In the space below draw a diagram of the above microscopic slide.
Label the neurones, cell body and nucleus.
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Drawing of micrograph of neurones
Name the features seen on the micrograph of neurones as seen through a
light microscope.
_________________________________________________________
_________________________________________________________
Check your answers.
The nerve impulse
When an atom or a group of atoms is electrically charged it is called an
ion. Some ions within cells are positive (calcium ion Ca+, sodium ion
Na+, potassium ion K+) while others carry a negative charge (chloride Cl–
and some proteins). Cells are surrounded by a semipermeable membrane
that controls the passage of ions into and out of the cell. In the
membrane are ion channels that allow particular ions to pass through.
The difference between the concentration of particular chemical ions
inside and outside of a cell results in a negative electrical charge within a
neurone. If a positive charge occurs in a neurone it will be passed to the
next neurone as a voltage pulse.
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Resting potential
At rest the inside of a neurone is negative compared to the outside of the
neurone. This charge is obtained by potassium ions (K+) passing easily
through the membrane to the outside while chloride ions (Cl–) and
sodium ions (Na+) cannot cross as freely. The negatively charged
proteins within the neurone are also prevented from crossing the
membrane. As well as ion channels in the membrane there are ion
pumps. These use energy to move more ions across the membrane.
All of this results in the resting potential being a negative charge of
–70 millivolts within the neurone.
Action potential
An action potential is the name given when a neurone sends an impulse
to the next neurone. It occurs when there is a rapid movement of
potassium and sodium ions across the cell membrane. When a neurone is
stimulated the first response is for sodium channels to open and this
results in sodium ions rushing into the cell. The positive charge on the
sodium ions depolarises the cell and the overall negative charge starts to
fall towards zero. When it reaches approximately –55 millivolts the
neurone will fire and an impulse or spike will occur. This is the
threshold for the reaction. It is a non-graded or ‘all or none’ response.
It is called an ‘all or none’ response because there is no variation in the
response. It either fires completely or not at all. Therefore if the
stimulus is not great enough to reach the threshold level the neurone will
not fire. Following the opening of the sodium channels, the potassium
channels open and potassium moves out of the cell. This repolarises the
cell and it moves back towards the resting potential. The time taken to
return to the resting potential is known as the refractory period.
During this time the neurone cannot fire again.
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Potential across plasma membrane (mV)
action potential
0
threshold level
–50
–70
resting potential
resting potential
refractory
period
0
1
2
3
4
5
6
Time (ms)
Graph of a typical action potential
Present information from secondary sources to graphically represent a
typical action potential.
Hint
The diagram above is one example of a graphical representation of a typical
action potential.
Animations are good graphical representations as well. Visit the LMP
Science Online website for this module to view some of these animations at:
http://www.lmpc.edu.au/science
Do Exercise 6.2 looking at the action potential of a neurone.
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The brain
The brain is a large organ located within the protective skull. It is
important as it controls the functioning of the rest of the body. It is the
location of emotions and thought. Any damage to the brain results in
changes to behaviour and coordination of the body. The three parts of
the brain that you will be looking at are the cerebrum, the cerebellum and
the medulla oblongata.
cerebrum
cerebral cortex
medulla oblongata
cerebellum
Three parts of brain: cerebrum, cerebellum and the medulla oblongata.
Cerebrum
The cerebrum is the most obvious and largest part of the brain. It is
highly folded therefore increasing the surface area available within the
small size of the skull.
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The human brain showing the highly folded nature of the cerebrum.
(Photo: © LMP)
When viewed from above the human brain is divided into two
hemispheres. The left hemisphere controls the right side of the body
while the right hemisphere controls the left side of the body.
The cerebrum is divided into the following lobes:
•
frontal
•
parietal
•
occipital
•
temporal.
Locate these lobes of the diagram following.
parietal lobe
frontal lobe
occipital lobe
temporal lobe
Lobes of the cerebrum
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Frontal lobe
The frontal lobes are located behind the forehead at the front of the head.
This part of the brain is involved in ‘higher order’ thinking.
This includes planning, problem solving and personality. It is the
location of ‘consciousness’. In the lower part of the left frontal lobe is
Broca’s area an important area for speech production.
Parietal lobe
The parietal lobes are at the top of the head towards the back. This area
is especially important for interpreting sensory signals including sight
and sound.
Occipital lobe
These lobes are located at the back of the head. The occipital lobe is
concerned with vision as well as other perceptions such as touch,
pressure, temperature and pain. It is the site of the visual cortex.
Temporal lobe
The temporal lobes are located at the side of the head above the ears.
This area interprets the impulses from the ears and gives meaning to the
information. It is an important region for the sense of hearing.
Wernicke’s area is in this region and is responsible for speech and
language function.
Do Exercise 6.3 now.
Cerebellum
Beneath the hemispheres of the brain there is the cerebellum. This part
of the brain is concerned with coordination. It receives information
about the position of joints and muscles. It also has a role in learning and
in hand-eye coordination.
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Medulla oblongata
The medulla oblogatais part of the brain stem and continues into the
spinal cord. It controls functions such as breathing, vomiting, digestion
and heart rate.
Perform a first-hand investigation to examine an appropriate mammalian
brain or model of a human brain to gather information to distinguish the
cerebrum, cerebellum and medulla oblongata and locate the regions involved
in speech, sight and sound perception.
If you are carrying out a first-hand investigation of dissecting an appropriate
mammalian brain such as a sheep’s brain make sure that you have assessed
the possible risks before you start. If you are using a sharp cutting
instrument be aware of cutting injuries. Have first aid equipment available
to treat any cuts. Have plenty of newspaper to work on and to wrap up the
dissection when you finished. Make sure that you dispose of any waste
safely in a garbage bin. Wear covered shoes in case you drop the
cutting instrument.
A dissection of a sheep’s brain is available as a webpage on the LMP
Science Online web site for this module at: http://www.lmpc.edu.au/science
Dissection of a sheep’s brain
You can obtain a sheep’s brain from your local butcher.
You will need:
•
a cutting board
•
a sheep’s brain
•
a scalpel or knife
•
newspaper.
Aim
To carry out a dissection of a sheep’s brain to distinguish the cerebrum,
cerebellum and medulla oblongata and locate the regions involved in
speech, sight and sound production.
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Method
Step 1
Place the sheep’s brain on the cutting board.
External features of a sheep’s brain
Without cutting anything examine the outside of the brain and find the
following; cerebrum, cerebellum and medulla oblongata.
cerebellum
cerebrum
(Photo: © LMP)
The underside is best to see the medulla oblongata.
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(Photo: © LMP)
Step 2
Cut the brain longitudinally as shown in the photograph below.
Taking a longitudinal section. (Photo: © LMP)
You should be able to see the leaf-like structure of the cerebellum at the
rear of the brain.
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Leaf-like cerebellum. (Photo: © LMP)
Step 3
Now cut a transverse section across the cerebrum.
Cutting a transverse section of the cerebrum. (Photo: © LMP)
The dark coloured material at the top of the cerebral cortex is the ‘grey’
matter. This is where the cell body containing the nucleus of the
Part 6: It’s all in the head
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neurones is found. The central ‘white’ matter is where the long axons of
the neurones are located. Identify these regions.
Grey and white matter in the cerebrum. (Photo: © LMP)
Step 4
Locate the regions of the brain that are involved in speech sight
and sound production by using the diagrams following.
The temporal lobe of the cerebrum is the auditory cortex. It controls speech
and hearing. (Photo: © LMP)
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occipital lobe
The occipital lobe of the cerebrum is the visual cortex. It is involved in sight.
(Photo: © LMP)
Results
Draw a longitudinal section of the brain in the space below. Locate and
name the cerebrum, the cerebellum and the medulla oblongata. Shade in
the areas involved in speech sight and sound.
Conclusion
A detailed drawing of the sheep’s brain was done showing the location of
the cerebrum, cerebellum and medulla oblongata and also the regions
involved in speech, sight and sound production.
Do Exercise 6.4 now.
Part 6: It’s all in the head
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Looking at a model brain
If you are unable to get a sheep’s brain for dissection then the alternative
is to look at a model of a human brain. Below are two photographs of
human brain models. The first shows the external features of the brain
including the cerebrum, cerebellum, medulla oblongata and the spinal
cord. Locate all of the features from the photograph.
cerebrum
cerebellum
medulla oblongata
spinal cord
(Photo: © LMP)
If the brain is cut between the hemispheres than the view below can
be seen.
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cerebrum
corpus callosum
medulla oblongata
cerebellum
spinal cord
Model of the human brain cut in a longitudinal section. (Photo: © LMP)
As well as these major structural areas there are areas associated with
sound or visual perception. These are in the visual cortex and the
auditory cortex. Other important areas dealing with sound and visual
perception are Broca’s area and Wernicke’s area. These are illustrated
on the diagram following.
motor cortex
sensory cortex
parietal lobe
Wernicke’s area
(comprehension of
language)
frontal lobe
occipital lobe
(visual cortex)
Broca’s area
(speech)
temporal lobe
(auditory cortex)
cerebellum
brain stem
Diagram of brain areas
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Brain area
Function
visual association area
processing of visual information
visual cortex
detection of information from the eye
auditory association area
processing of audio stimulus
Wernicke’s area
language
auditory cortex
detection of sound
Broca’s area
speech production
Do Exercise 6.5. Examining a model human brain.
Interpretation of sensory signals
The brain interprets the incoming sensory signals for the organs of
perception throughout the body. Using this information the behaviour of
an animal is coordinated. Behaviour is the actions of an organism. If the
information is not correctly interpreted this will lead to abnormal
behaviour in the animal.
Any damage to the brain can lead to misinterpretation. Two examples of
incorrect interpretation of sensory signals are:
•
Wernicke’s aphasia
•
Broca’s aphasia.
Wernicke’s aphasia
The condition was recognized in 1874. A patient who was unable to
comprehend language but was capable of speech was found to have a
brain tumor on the brain in this area called Wernicke’s area after its
discoverer. This condition may also be caused by stroke or head injury.
Wernicke’s area is usually located on the left side of the brain in the
temporal lobe close to the junction with the parietal lobe. It is not found
in exactly the same location in every brain. It is important in
understanding language. If there is damage to this area then a condition
known as Wernicke’s aphasia occurs. People with this condition cannot
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understand language but can still make sounds. They can hear and read
words but not understand the information that is conveyed in the
sounds or words. This leads to confusion and this may lead to
behavioural changes.
Broca aphasia
Another important area in sound perception is Broca’s area. It is located
in the lower part of the left frontal lobe. Damage to this region results in
the understanding of what is said but the inability to produce sounds to
reply. The damage prevents people from producing speech or otherwise
the speech is slurred and slow.
Do Exercise 6.6 now.
This completes the Option Communication.
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Summary
First-hand investigations
There were two first-hand investigations to do in this part:
•
perform a first-hand investigation using stained prepared slides
and/or electron micrographs to gather information about the structure
of neurones and nerves
•
perform a first-hand investigation to examine an appropriate
mammalian brain or model of a human brain to gather information to
distinguish the cerebrum, cerebellum and medulla oblongata and
locate the regions involved in speech, sight and sound perception.
Secondary information
During this part of the module you should have carried out the following
task using secondary information.
•
Present information from secondary sources to graphically represent
a typical action potential.
Summary
The interpretation of sensory information occurs in the brain. The basic
unit of the nervous system is the neurone or nerve cell. The neurone
consists of dendrites, the cell body and an axon. Between neurones there
is a gap known as a synapse. The impulse across the synapse involves
chemicals known as neurotransmitters. The impulse that travels along
the neurone is an electrical signal while the crossing of the synapse is
chemical. This explains that the nerve impulse consists of electro
chemical signals.
A nerve is a collection of neuronal fibres (axons and dendrites). When a
neurone sends an impulse it is called an action potential. This follows an
Part 6: It’s all in the head
25
‘all-or-none’ response. After firing a neurone is unable to fire again for a
certain period of time known as the refractory period.
The main areas of the brain are the cerebrum, cerebellum and the
medulla oblongata. The cerebrum forms a large part of the brain.
The areas involved in perception are the visual cortex and auditory
cortex, Wernicke’s area and Broca’s area. If the brain is damaged there
may be aphasia and the behaviour of the organism is affected.
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Suggested answers
Your answer should be similar to this answer. If your answer is very
different or if you do not understand an answer, contact your teacher.
Microscopic examination of a neurone
The main features visible in the micrograph of neurones as seen through
a light microscope are the cell body and nucleus.
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Exercises – Part 6
Exercises 6.1 to 6.6
Name: _________________________________
Exercise 6.1: Nerves and neurones
a)
What is a neurone?
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) In the space below, draw a simple diagram of a neurone labeling the
cell body, dendrites, axons, axon terminals, myelin sheath and cell
nucleus.
c)
What is a nerve?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
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d) Draw in the space below a nerve showing the bundles of neuronal
fibres.
Exercise 6.2: The action potential
a)
Define the term threshold and explain why not all stimuli generate
an action potential.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
b) Describe the transmission of a signal from one neurone to the next.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
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Draw a graphical representation of an action potential.
Potential across plasma membrane (mV)
c)
0
threshold level
–50
–70
0
1
2
3
4
5
6
Time (ms)
Exercise 6.3: The brain
a)
Name the four lobes of the cerebrum.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) For each lobe describe its function.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
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Exercise 6.4: Dissection of a sheep’s brain
During your Biology course you would have carried out a dissection off a
sheep’s brain.
a)
Outline the steps you used during the investigation.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
b) What possible risks did you identify and what did you do to reduce
these risks?
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
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Exercise 6.5: Model of a human brain
a)
On the photograph below of a human model brain label the
cerebrum, the cerebellum, the medulla oblongata or the brain stem.
(Photo: © LMP)
b) On the diagram below identify those areas of the cerebrum involved
in the perception and interpretation of light and sound including the
visual cortex, the auditory cortex, Wernicke’s Area and
Broca’s Area.
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Exercise 6.6: Interpretation of sensory signals
Explain, using specific examples, the importance of correct interpretation
of sensory signals by the brain for the coordination of animal behaviour
Example 1_________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Example 2_________________________________________________
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34
Communication
Student evaluation of the module
Name: ________________________
Location: ______________________
We need your input! Can you please complete this short evaluation to
provide us with information about this module. This information will
help us to improve the design of these materials for future publications.
1
Did you find the information in the module clear and easy to
understand?
_____________________________________________________
2
What did you most like learning about? Why?
_____________________________________________________
_____________________________________________________
3
Which sort of learning activity did you enjoy the most? Why?
_____________________________________________________
_____________________________________________________
4
Did you complete the module within 30 hours? (Please indicate the
approximate length of time spent on the module.)
_____________________________________________________
_____________________________________________________
5
Do you have access to the appropriate resources? eg a computer, the
internet, scientific equipment, chemicals, people that can provide
information and help with understanding science
_____________________________________________________
_____________________________________________________
Please return this information to your teacher, who will pass it along to
the materials developers at OTEN – DE.
BIOHSC43457 Communication
Learning Materials Production
Open Training and Education Network – Distance Education
NSW Department of Education and Training