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Special Senses:
Hearing, Taste, Smell
Peripheral Nervous System
Chapter 15
The Senses
 General senses of touch (tactile)
 Temperature - thermoreceptors (heat)
 Pressure - mechanoreceptors (movement)
 Pain - mechanoreceptors
 Special senses
 Smell - chemoreceptors (chemicals)
 Taste - chemoreceptors
 Sight - photoreceptors (light)
 Hearing - mechanoreceptors
 Equilibrium - (balance) mechanoreceptors
The Ear: Hearing and Balance

Two functions: Hearing and Balance
 Hearing:
Sound vibrations
 Equilibrium: Gross movements
 Mechanoreceptors:
respond to physical forces
 Both respond to different stimuli and
activated separately
Anatomy of Ear
HEARING
ONLY
HEARING
&
BALANCE
Anatomy of Ear
Why do we need earwax???

Divided into 3 regions:
 External,
Middle,
Internal
Earwax
protects
delicate
lining of meatus
(auditory canal) and helps prevent
 External Ear
microorganisms from entering the ear
 Auricle
(pinna) and Auditory Canal
 Ceruminous Glands in canal secrete earwax
 Tympanic membrane - eardrum
Anatomy of Ear

Middle Ear
 Tympanic
Cavity – air filled, mucosa-
lined
 Eustachian Tube – connects to throat
 Auditory ossicles (tiny bones) –
hammer, anvil, stirrup
Pressure build up
Swallowing
yawning
“VALSALVA”
Eustacian tube
THROAT
Otitis media
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http://www.petearclinic.com/images_video.htm

http://apps.uwhealth.org/health/hie/2/19596.htm
Middle ear inflammation
Common with sore
throat in children
Enlarge, inflamed
eardrum
Pus, fluid build up
requires incision and
tubes to relieve pressure
and drain
Anatomy of Ear

INNER EAR
 This is a cavity
 Bony labyrinth – bony
chamber divided into
3 regions
Cochlea
 Vestibule
 Semicircular Canals


Two fluids:
Endolymph
 Perilymph

Labyrinth:
an intricate, sometimes
confusing, arrangement or
pattern
Hearing
Sound waves > eardrum > ossicles >
oval window > set fluid in motion >
vibrations stimulate “hair
cells”
> cochlear
Within
Cochlear
duct,
membranous
labyrinth
nerve transmits impulse
to midbrain
> is
Spiral
Organ of
Corti –
auditory cortex of
temporal
lobe
hearing receptors or “hair
cells”
Figure 8.15
How the ear works…

http://www.youtube.com/watch?v=dCyz8eAs1I
Chemical Senses: Taste and Smell

Chemoreceptor – respond to chemicals in
solution
OLFACTORY = smell
 GUSTATORY = taste




Five types of receptors for taste
Olfactory receptors much more sensitive
Complement each other, respond to same
stimuli
 Smell not as good as animals; however, some people
are wine tasters, perfumers
 If you smell a particular odor all day, you won’t
recognize its presence, you become accustomed, ex.
garbage men
 Old people lose sense of smell- lots of perfume
 Humans can distinguish 10,000 or so chemicals
 What we really smell is pain: ex. chili, ammonia,
menthol (cold)
 Specific chemicals cause specific patterns of neurons
to fire
Olfactory
epithelium
Olfactory tract
Olfactory bulb
Nasal
conchae
(a)
Route of
inhaled air
Figure 15.21a
Olfactory Receptors: Smell

1000’s of olfactory receptors roof of nasal cavity

Sniffing intensifies sense of smell

Olfactory receptor cells have olfactory hairs –
long cilia – in mucus layer

Chemicals in mucus layer stimulate hairs ->
filaments -> nerve

Olfactory impressions long lasting – memories,
adaptive
Figure
8.17
Olfactory
tract
Mitral cell (output cell)
Glomeruli
Olfactory bulb
Cribriform plate of ethmoid bone
Filaments of olfactory nerve
Olfactory
gland
Lamina propria connective tissue
Axon
Basal cell
Olfactory receptor cell
Olfactory
epithelium
Supporting cell
Mucus
(b)
Dendrite
Olfactory cilia
Route of inhaled air
containing odor molecules
Figure 15.21a
Pathway of smell
Nostril > nasal cavity > olfactory
receptors (sensory neurons) in membrane
(top of nasal cavity) > through ethmoid
(bone) > olfactory neurons in
olfactory bulb > brain

http://www.youtube.com/watch?v=dIDBGUPRUI
Taste Buds and Taste

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Most pleasurable sense
Approx. 10,000 taste
buds, most on tongue
Papillae – projections,
taste buds found on
sides


Circumvallate papillae –
sides of tongue
Fungiform papillae –
top, more numerous
Figure 8.18
Taste Buds
Filiform
papilla
Fungiform
papilla
Circumvallate Papilla
Connective tissue
Tongue epithelium
Taste Buds

Gustatory cells – respond
to chemicals
 Gustatory
Chewed food mixes with
saliva hairs
> –
microvilli,
protrude >
solution slides down to sides
of papillae
through taste
pore
enters taste pore > stimulate
gustatory
hairs > stimulate gustatory receptor cells >
impulse travels by nerves to brain
Figure 8.18
Five Taste Sensations
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SWEET – sugars, saccharine,
some a.a., lead salts
SOUR -- acids
BITTER – alkaloids
SALTY – metal ions in
solution
UMAMI– a.a. glutamate,
“beef taste” and MSG
Only slight differences in
receptor location.
Most buds respond to 2+
stimuli
http://pactlab-dev.spcomm.uiuc.edu/classes/08SP/280blogs/first_weblog3/2008/02/digitizing-your-taste-buds.html
Taste

Homeostatic role
Tastes for salt or sugar – minerals or carbs
 Sour – Oranges, lemons – Vitamin C
 Umami – protein intake
 Bitter – most poisons and spoiled food bitter,
protective
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Factors of Taste

Temperature, texture

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Spicy food excites pain receptors in mouth
Taste and Smell Complementary

Eating when you have cold
Loss of Chemical Senses

Beginning in 40’s ability to taste and smell
diminishes
Decrease in # of receptors
 About 50% over 80 cannot smell
 Sense of taste is poor
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The End