Special Senses
Ch. 10
Sensory functions
1. Sensory pathways begin with
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Stimulus
Receptor
CNS
2. Receptors
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Vary in structure
They all excite
Stimulus specific
Sensory adaptation: decrease rates of stimuli
3. Receptor types: classified by sensitivity
a. Mechanoreceptors
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Mechanical or physical change
Touch. Pressure, tension, hearing,
equilibrium, & BP
1.Meissner’s corpuscles (touch)
-Found in fingers, palms, soles,
lips external genitalia
2. Merkel’s disc’s (touch)
-End in epidermis
3.Pacinian Corpuscles (pressure)
-Joints, tendons, visceral organs
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Proprioceptors (positional)
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Stretch, tension, position
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muscle, tendons, ear
• Muscle spindles
• Golgi tendon organs
• Thermo receptors
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Temperature changes
Free nerve endings in the skin
<10 ° C - >45° C pain is also triggered
Nociceptors
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Pain from chemical or physical damage
Protective function
Free nerve endings in skin, muscle, organs
Can be generated by other receptors
Referred pain
Photoreceptors
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Changes to amount of light
Only in retina of eye
Chemoreceptor
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Detect chemicals dissolved in
fluid/air
Smell & taste
Provide detection of O2 & CO2 in
blood
4. Sensory pathway
a. General: skin or visceral organs
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1st order neuron-2nd-3rd order to cortex for
processing
b. Special: special sensory organs( eye/ear)
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More variation& # of neurons used
Route impulse to specialized areas of brain
Special Senses
5. Smell: olfaction
a. Chemoreceptor in nasal cavity
b. Olfactory bulb located high in nasal
cavity
c. Detect ~50 smells
d. Neuron travels through cribiform
plate
e. How it works
• Chemicals dissolve in mucous & cause nerve impulse
• Olfactory nerve to frontal lobe/interpretation
• Closely linked to limbic system
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emotional expression
smells can trigger memories/emotions
6. Taste: gustation
a. Associated with smell
b. Both chemoreceptors
c. receptor: taste bud
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10,000 on tongue
infants all over mouth
located on surface of pappilae
gustatory cells/supportive epithelial cells
1. taste hairs( microvilli)
2. taste pores
3. 4 tastes
• sweet
• sour
• salty
• bitter
7. Sight
a. Eyes & accessory structures
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Eye lids: protection
Lashes: protection
Conjunctiva: inner membrane of lid & eye
1. secretes mucous to lubricate eye
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Lacrimal apparatus/gland-duct-sac
1. secrete tears
2. lubrication/antibacterial
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Nasolacrimal duct: empty tears into nasal cavity
muscles
Lateral rectus
VI
Lateral eye movement
Medial rectus
III
Medial eye movement
Superior rectus
III
Elevates/rolls eye upward
Inferior rectus
III
Depresses/rolls eye downward
Superior oblique
III
Elevates & turns eye laterally
Inferior oblique
IV
Depresses and turns eye laterally
b. Eye structure
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Fibrous tunic: thick outermost layer of eye
1. sclera: white of eye
2. cornea: clear front of eye
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Vascular tunic
1. choroids: thin, dark brown membrane
a. absorbs light/minimize reflection
b. vessels nourish the retina
2. ciliary body: connects to lens by
suspensory ligaments
3. iris: attached to ligaments
a. colored part of eye
b. controls light
4. pupil: opening in center of iris
5. lens: elastic structure that helps focus
image
a. accomodation
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Cavities
1. Anterior Cavity: cornea & lens
a. Contains aqueous humor: watery fluid bathes eye
b. Anterior chamber: cornea to iris
c. Posterior chamber: iris to lens
2. Posterior Cavity: behind lens
a. contains vitreous humor: gel-like support of eye
2
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Nervous tunic
1. retina: inner lining of posterior wall
a. detects light- optic nerve
2. photoreceptor cells
a. rods: light intensity
- low light/ shades of grey
- rhodopsin: visual purple
b. cones: color sensitive
-need more light/sharper vision
-red(erythrolabe), green(chlorolabe),
blue(cyanolabe
3. optic disc: “blind spot”
a. area where optic nerve leave back of eye
4. macula lutea: yellowish spot on back of eye
5. fovea centralis: high concentration of cone cells only
a. sharpest vision area
4
4./5
3.
c. eye function
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path of light
1. light is refracted as is passes into the eye
2. image is focused on the retina
3. image is upside down, smaller and reversed left from
right ( due to refracting light)
4. brain coordinates proper image in visual
interpretation center
vision
problems
a. image focused in front of retina
1. myopia: nearsightedness
b. too much refraction
c. eye is too long
2. hyperopia: farsightedness
A, image focus is behind retina
b. weak or lazy lens
c. eye that is too short
3. astigmatism
a. unequal curvatures of the
cornea or lens
b. blurred vision near & far
Because of 2 focal points
Vision disease
4. Color blindness
a. Absence of one or more cone cells
b. hereditary condition
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-sex-linked.
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- 1-30 people, 1-12 men affected
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- most common is red-green
Vision Problems
5. Cataract
a. Lens or cornea become cloudy or opaque
b. Light is scattered and causes blurred vision
Vision disease
6. Glaucoma
a. Aqueous humor formation exceeds rate of removal
-usually from blockage/restriction of drain
b. Increases eye pressure
c. Decreases blood supply to retina
d. Can cause permanent blindness
Visual Acuity
Snellen Eye chart
20/20: what a normal person
can see from 20 feet.
20/10: what you can see @ 20
feet a normal person has to
see @ 10 feet.
20/100: what a normal person
can see @ 100 feet you see
@ 20
Astigmatism Test
: curvature of the eye is unequal
If lines appear darker in one
direction then there is an
astigmatism.
The ear
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The ear
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- has external, middle and inner parts
organ of hearing & equilibrium
II. External Ear
1. auricle or pinna
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-outer funnel-like structure
-collects sound waves
2.External auditory meatus
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S- shaped tube that passes through the temporal Bone
carries sound waves to ear drum
hair & ceruminous glands (Cerumen) protect ear
III. Middle Ear
1.Typanic membrane “ear drum”
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outer surface- Thin skin layer
inner surface- mucous membrane
oval-cone shape; apex is attached to auditory ossicles
( malleous)
sound waves cause pressure changes- which results in
movement of the ear drum and the auditory ossicles
2. Auditory ossicles
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thin bones in the inner ear
Malleous (hammer) attach to ear drum , attaches to
incus (anvil) & stapes (stirrup) attaches to the oval
window on tympanic cavity
lever system that increases/amplifies
vibration=22x@ oval window
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tympanic reflex- muscles that make
middle ear more rigid reducing
vibration= muffles loud sounds
3. Auditory (eustachian ) tube
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connect middle ear to throat
helps maintain air pressure balance on each side
of the tympanic membrane (ear drum) needed for
normal hearing
IV. Inner ear
1. Labyrinth
• complex system of interconnected tubes & chambers
• osseous labyrinth- bony canal in temporal b.
• membranous labyrinth- tube within the osseous labyrinth filled
with liquid = endolymph
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A. Semicircular canals
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provide sense of equillibrium
3 axis
B. Cochlea
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coiled, bony canal connected to oval window & round
window
round window dissipates vibrations through cochlea
i. Organ of Corti (microphone)
- contains hair like hearing receptors
- stimulated by vibrations through endolymph
- receptor frequency differentiated
- receptors move against tectoral membrane
- epithelial cells that act like neurons
- transmit to vestibulocochlear N.(VIII)
cochlear branch- hearing
vestibular branch- equilibrium
How we hear
 http://msjensen.cehd.umn.edu/1135/Links/
Animations/Flash/0019swf_effect_of_soun.swf
 http://www.sumanasinc.com/webcontent/a
nimations/content/soundtransduction.html
V. Equilibrium
1. Static : position of head & body when motionless
A. Structures
- receptors located in vestibule
(bony chamber between cochlea & semicircular canals)
-utricle & saccule chambers inside vestibule
- contain hair cells & supporting cells called _macula
-cells have vertical or horizontal orientation inside chambers
- otolithic membrane- gelatinous material
- otoliths-calcium carbonate crystals give weight to O.M.
b. How it works
1. head moves
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O.M. moves across hair cells & macula causing them to
bend
nerve impulses sent via the vestibulocochlear n. to the
CNS
2. Dynamic- sense of position when body is
moving
a. structures
-semicircillar canals occupy the 3 planes
- ampulla -swelling at end of canal
communicates with utricle
- crista ampullaris sensory hair cells
(similar to macula)
-cupula - gelatinous mass in canal
b. How it works
1. movement of head causes canal to
move with head
2. Cupula stays stationary because of inertia
3. Movement bends hair cells in opposite
direction of movement
4. Impulse sent via vestibulocochlear n.
 Side
note:
Brain gains other information about equilibrium from Proprioceptors
(mechanoreceptors) and visual input from the _eyes.
How it works
http://www.sumanasinc.com/webcontent/animations/content/vestibular.html