Special Senses: Hearing, Taste, Smell Peripheral Nervous System Chapter 8

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

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 Crash Course: Hearing & Balance Sound vibrations move fluid and stimulate hearing receptors Gross movements of the head disturb fluids surrounding the balance organs.

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.

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.

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

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

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 > external acoustic meatus eardrum vibrates > ossicles set into motion > oval window on vestibule > set fluid in motion > vibrations stimulate “hair cells” in cochlea> vestibulocochlear 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

Cochlear HAIR CELLS Determine volume and pitch Volume = the higher the volume, the more hair cells are stimulated Pitch = the higher the pitch, the faster they move and the lower the pitch, the slower they move

How the ear works… http://www.youtube.com/watch?v=dCyz8-eAs1I What is a cochlear implant? https://www.youtube.com/watch?v=zeg4qTnYOpw Cochlear implants https://www.youtube.com/watch?v=6FhgYcfZZY8

Hearing Loss The following factors contribute to age-related hearing loss: Family history (tends to run in families) Repeated exposure to loud noises Smoking (smokers are more likely to have such hearing loss than nonsmokers) Certain medical conditions and medications also contribute to age-related hearing loss. About half of all people over age 75 have some amount of age-related hearing loss.

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 Crash Course: TASTE & SMELL

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 During old age, 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

How the nose works… http://www.youtube.com/watch?v=dIDBG-UPRUI

Olfaction Olfactory epithelium Olfactory tract Olfactory bulb Nasal conchae Route of inhaled air (a) 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

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

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

Taste Buds and Taste Most pleasurable sense Approx. 10,000 taste buds, most on tongue Papillae – projections that hold taste buds Circumvallate papillae – back of tongue; taste buds on sides Fungiform papillae – top of tongue; taste buds on sides; more numerous Filiform papillae – sides of tongue; taste buds on top Some soft palate and cheeks Figure 8.18

How the tongue works… https://www.youtube.com/watch?v=KuP-Kj7MHes

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

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

Five Taste Sensations SWEET – sugars, saccharine, salts SOUR -- acids BITTER – alkaloids SALTY – metal ions in solution UMAMI– 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 Taste and Smell Complementary Spicy food excites pain receptors in mouth Taste and Smell Complementary Eating when you have cold Ghost chile pepper from India Heat Exceptionally hot Scoville rating 330,000–1,000,000 liquid Oleoresin Capsicum

Loss of Taste & Smell Beginning in 60’s ability to taste and smell diminishes Decrease in # of receptors About 50% over 80 cannot smell Sense of taste is poor

Loss of Taste & Smell Various other factors also can contribute to loss of taste and smell, however, including: Nasal and sinus problems, such as allergies, sinusitis or nasal polyps Certain medications, including beta blockers and angiotensin-converting enzyme (ACE) inhibitors Tooth decay or poor dental hygiene Cigarette smoking Head or facial injury Alzheimer's disease Parkinson's disease

Impact of LOSS Quality of life, often leading to decreased appetite and poor nutrition Contributes to depression Might tempt you to use excess salt or sugar on your food to enhance the taste — which could be a problem if you have high blood pressure or diabetes

Flavor Lab See instructions on worksheet

Homeostatic Imbalances of the EAR & NOSE Disorder Cause Effect Otitis media (292) Skip 3-4 lines Conduction deafness (297) Sensorineural deafness (297) Anosmias (300)