Special Senses: Hearing, Taste, Smell

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

2. 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 Senses

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

4. Anatomy of Ear HEARING & BALANCE HEARING ONLY

5. Anatomy of 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

6. 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

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 http://www.petearclinic.com/images_video.htm http://apps.uwhealth.org/health/hie/2/19596.htm

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” Figure 8.15

10. How the ear works… http://www.youtube.com/watch?v=dCyz8-eAs1I

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. Olfactory epithelium Olfaction 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 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 http://www.youtube.com/watch?v=dIDBG-UPRUI

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 Figure 8.18

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

21. Taste Buds 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 http://pactlab-dev.spcomm.uiuc.edu/classes/08SP/280blogs/first_weblog3/2008/02/digitizing-your-taste-buds.html

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 • 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