Sensory
Receptors
Receptors
• There are millions of receptors all over the
body. Receptors may be simple naked nerve
endings, encapsulated nerve endings or
complex structures.
• Receptors detect stimuli (internal or external)
& convert them to nerve impulses
The sensory receptors
Each sensory system has three component parts:
1)Sensory receptors which are the branched
endings of sensory neurons or specialized cells
adjacent to them that detect specific stimuli.
2)Nerve pathways lead to the brain.
3)Brain regions process the information into a
sensation; later, perhaps, a perception
(understanding) of the sensation will be made.
How does a sensory receptor work?
• Some sensory receptors are activated when
they are bent, squished, or disturbed in some
way.
• Others are activated by chemicals.
• Others by temperature.
• And others by light.
• Whatever the outside world influence is, we
can call it a stimulus for the receptor
• Whatever the appropriate stimulus is, that will cause a
depolarization to occur in the sensory receptor cell
• The depolarization within the sensory dendrite itself
(due to the stimulus) is called a receptor potential
• When the dendrite is deformed, its membrane stretches,
and ions can flow through the stretch-gated channels. If
this occurs enough, there will be enough of a receptor
potential to trigger an action potential.
In summary
Sense of touch
• Touch may be considered one of
five human senses; however,
when a person touches
something or somebody this gives
rise to various feelings: the
perception of pressure (hence
shape, softness, texture,
vibration, etc.), relative
temperature and sometimes pain.
• The term "touch" is usually
replaced with somatic senses,
to better reflect the variety of
mechanisms involved
• Free nerve endings are simply branched endings of sensory
neurons in the skin that function as mechanoreceptors,
thermoreceptors, and pain receptors.
• Meissner corpuscles adapt slowly to vibrations of low
frequencies.
• The bulb of Krause is a thermoreceptor that is sensitive to
temperatures below 20 degrees C.
• Ruffini endings are sensitive to steady touching and
pressure, and to temperatures above 45 degrees C.
• Pacinian corpuscles are located both in the dermis and near
joints; they are able to detect rapid pressure changes
associated with touch and vibrations.
Sense of vision
• Vision requires a complex system
of photoreceptors and neural
program in the brain that can
interpret the patterns of action
potentials
• All photoreceptors incorporate
pigment molecules that can absorb
photon energy, which can be
converted into excitation energy in
sensory neurons.
• The photoreceptors are located in
the retina
Results
1.Normal Color Vision:
A: 29, B: 45, C: --, D: 26
2. Red-Green Color-Blind:
A: 70, B: --, C: 5, D: -3.Red Color-blind:
A: 70, B: --, C: 5, D: 6
4.Green Color-Blind:
A: 70, B: --, C: 5, D: 2
Sense of hearing
• Hearing is the perception of sounds, which
are traveling vibrations of mechanical
energy
Hearing test
• Normal human hearing ranges from 20 Hz to
20 kHz
• A gradual decline with age is considered
normal
The middle ear contains small bones with amplify the sounds
before transmittal to the inner ear.
The external ear in mammals has a pinna for collecting the
sounds.
In the cochlea of the inner ear, acoustical receptors in the
form of hair cells respond to pressure waves transmitted
through the surrounding fluid.
• Impulses are sent along the auditory nerve to the brain for
interpretation.
• The hair cells of the human ear can be permanently
damaged by prolonged exposure to intense sounds
Sense of smell
• Olfactory receptors are
responsible for our sense of
smell.
• They respond to a variety of
odour molecules
• Humans have about 5 million
olfactory receptor neurons
• Olfactory receptor neurons
reside on the olfactory
epithelium in the nasal cavity
Sense of taste
• Taste receptors enable
animals to distinguish
nutritious from noxious
substances.
Receptors of some animals
are located on antennae,
legs, tentacles, or fins.
In humans, taste receptors
are often components of
taste buds distributed
mostly on the tongue.
Questions
• What are receptors?
• What are the three components of the sensory
system?
• How many senses do we humans have? Five or more?
Name them
• How does a sensory receptor work? (Brief description)
• What is the name of the receptor involved in your
sense of smell?
• Where are the sense of taste receptors located in the
human body?