1. Special Senses: Hearing, Taste, Smell
Peripheral Nervous System
Chapter 15

2. The Senses General senses of touch (tactile) Special senses
Temperature - thermoreceptors (heat)
Pressure - mechanoreceptors (movement)
Pain - mechanoreceptors
Special senses
Smell - chemoreceptors (chemicals)
Taste - chemoreceptors
Sight - photoreceptors (light)
Hearing - mechanoreceptors
Equilibrium - (balance) mechanoreceptors

3. 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
Sound vibrations move fluid and stimulate hearing receptors
Gross movements of the head disturb fluids surrounding the balance organs.

4. Anatomy of Ear HEARING ONLY HEARING & BALANCE
External and Middle-Hearing only
Internal-both equilibrium and hearing
Auricle-focus sound into the auditory canal for most animals, for humans lost most function
Earwax-sticky trap for foreign bodies and repels insects, Cleaning your ears everyday
Sound waves travel down canal to eardrum.

5. Anatomy of Ear Divided into 3 regions: External Ear
Why do we need earwax???
Earwax protects delicate lining of meatus (auditory canal) and helps prevent microorganisms from entering the ear
Divided into 3 regions:
External, Middle, Internal
External Ear
Auricle (pinna) and Auditory Canal
Ceruminous Glands in canal secrete earwax
Tympanic membrane - eardrum
External and Middle-Hearing only
Internal-both equilibrium and hearing
Auricle-focus sound into the auditory canal for most animals, for humans lost most function
Earwax-sticky trap for foreign bodies and repels insects, Cleaning your ears everyday
Sound waves travel down canal to eardrum.

6. Anatomy of Ear Middle Ear Tympanic Cavity – air filled, mucosa-lined
Eustachian Tube – connects to throat
Auditory ossicles (tiny bones) – hammer, anvil, stirrup
Eustachian tube normally flattened or closed. Yawning or swallowing can open it to equalize pressure
Eardrum-hammer-anvil-stirrup-oval window-fluid in inner ear into motion stimulating hearing receptors
Pressure build up
Swallowing
yawning
“VALSALVA”
Eustacian tube
THROAT

7. Otitis media 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

8. 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

9. Hearing
Sound waves > eardrum > ossicles > oval window > set fluid in motion > vibrations stimulate “hair cells” > cochlear nerve transmits impulse to midbrain > auditory cortex of temporal lobe
Within Cochlear duct, membranous labyrinth is Spiral Organ of Corti – hearing receptors or “hair cells”
Lengths of fibers over region vibrate at certain frequencies. Shorter – high pitche sounds, hairs closer to oval circle, longer low pitched, further from circle
Figure 8.15

10. How the ear works…

11. 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

12. Facts About Smelling
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

13. Olfaction Olfactory epithelium Olfactory tract Olfactory bulb Nasal
conchae
Route of
inhaled air
(a)
Figure 15.21a

14. 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

15. Mitral cell (output cell)
Olfactory
tract
Mitral cell (output cell)
Glomeruli
Olfactory bulb
Cribriform plate of ethmoid bone
Filaments of olfactory nerve
Lamina propria connective tissue
Olfactory
gland
Axon
Basal cell
Olfactory receptor cell
Olfactory
epithelium
Supporting cell
Dendrite
Olfactory cilia
Mucus
Route of inhaled air
containing odor molecules
(b)
Figure 15.21a

16. 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

18. Taste Buds and Taste 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
Some soft palate and cheeks
Figure 8.18

19. Taste Buds Circumvallate Papilla Fungiform papilla Filiform papilla
Connective tissue
Tongue epithelium

21. Taste Buds Gustatory cells – respond to chemicals
Chewed food mixes with saliva > solution slides down to sides of papillae > enters taste pore > stimulate gustatory hairs > stimulate gustatory receptor cells > impulse travels by nerves to brain
Gustatory cells – respond to chemicals
Gustatory hairs – microvilli, protrude through taste pore
Figure 8.18

22. Five Taste Sensations
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

23. 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

24. Factors of Taste Temperature, texture Taste and Smell Complementary
Spicy food excites pain receptors in mouth
Taste and Smell Complementary
Eating when you have cold

25. 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

26. The End