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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 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 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 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 Factors of Taste Temperature, texture 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 The End