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

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 Two functions: Hearing and Balance Hearing: Sound vibrations Hearing: Sound vibrations Equilibrium: Gross movements Equilibrium: Gross movements Mechanoreceptors: respond to physical forces Mechanoreceptors: respond to physical forces Both respond to different stimuli and activated separately Both respond to different stimuli and activated separately

Anatomy of Ear HEARING ONLY HEARING & BALANCE

Anatomy of Ear Divided into 3 regions: External, Middle, Internal External Ear Auricle (pinna) and Auditory Canal Ceruminous Glands in canal secrete earwax Tympanic membrane - eardrum Why do we need earwax??? Earwax protects delicate lining of meatus (auditory canal) and helps prevent microorganisms from entering the ear

Anatomy of Ear Middle Ear Middle Ear Tympanic Cavity – air filled, mucosa- lined Tympanic Cavity – air filled, mucosa- lined Eustachian Tube – connects to throat Eustachian Tube – connects to throat Auditory ossicles (tiny bones) – hammer, anvil, stirrup Auditory ossicles (tiny bones) – hammer, anvil, stirrup Eustacian tube Pressure build up  Swallowing  yawning  “VALSALVA” 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

Anatomy of Ear INNER EAR INNER EAR This is a cavity This is a cavity Bony labyrinth – bony chamber divided into 3 regions Bony labyrinth – bony chamber divided into 3 regions Cochlea Cochlea Vestibule Vestibule Semicircular Canals Semicircular Canals Two fluids: Two fluids: Endolymph Endolymph Perilymph Perilymph Labyrinth: an intricate, sometimes confusing, arrangement or pattern

Figure 8.15 Hearing Within Cochlear duct, membranous labyrinth is Spiral Organ of Corti – hearing receptors or “hair cells” 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

How the ear works… eAs1I eAs1I eAs1I eAs1I What is a cochlear implant? Y8 Y8 Cochlear implants Y8 Y8

Hearing Loss The following factors contribute to age-related hearing loss: Family history (tends to run in families) Family history (tends to run in families) Repeated exposure to loud noises Repeated exposure to loud noises Smoking (smokers are more likely to have such hearing loss than nonsmokers) 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 Chemoreceptor – respond to chemicals in solution OLFACTORY = smell OLFACTORY = smell GUSTATORY = taste GUSTATORY = taste Five types of receptors for taste Five types of receptors for taste Olfactory receptors much more sensitive Olfactory receptors much more sensitive Complement each other, respond to same stimuli 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  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… UPRUI UPRUI UPRUI UPRUI

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

Olfactory Receptors: Smell 1000’s of olfactory receptors roof of nasal cavity 1000’s of olfactory receptors roof of nasal cavity Sniffing intensifies sense of smell Sniffing intensifies sense of smell Olfactory receptor cells have olfactory hairs – long cilia – in mucus layer Olfactory receptor cells have olfactory hairs – long cilia – in mucus layer Chemicals in mucus layer stimulate hairs -> filaments -> nerve Chemicals in mucus layer stimulate hairs -> filaments -> nerve Olfactory impressions long lasting – memories, adaptive Olfactory impressions long lasting – memories, adaptive Figure 8.17

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

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 Most pleasurable sense Approx. 10,000 taste buds, most on tongue Approx. 10,000 taste buds, most on tongue Papillae – projections, taste buds found on sides Papillae – projections, taste buds found on sides Circumvallate papillae – sides of tongue Circumvallate papillae – sides of tongue Fungiform papillae – top, more numerous Fungiform papillae – top, more numerous Figure 8.18

How the tongue works… Kj7MHes Kj7MHes Kj7MHes Kj7MHes

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

Taste Buds Figure 8.18 Gustatory cells – respond to chemicals Gustatory cells – respond to chemicals Gustatory hairs – microvilli, protrude through taste pore Gustatory hairs – microvilli, protrude through taste pore 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

Five Taste Sensations SWEET – sugars, saccharine, some a.a., lead salts SWEET – sugars, saccharine, some a.a., lead salts SOUR -- acids SOUR -- acids BITTER – alkaloids BITTER – alkaloids SALTY – metal ions in solution SALTY – metal ions in solution UMAMI – a.a. glutamate, “beef taste” and MSG UMAMI – a.a. glutamate, “beef taste” and MSG Only slight differences in receptor location. Only slight differences in receptor location. Most buds respond to 2+ stimuli Most buds respond to 2+ stimuli

Taste Homeostatic role Homeostatic role Tastes for salt or sugar – minerals or carbs Tastes for salt or sugar – minerals or carbs Sour – Oranges, lemons – Vitamin C Sour – Oranges, lemons – Vitamin C Umami – protein intake Umami – protein intake Bitter – most poisons and spoiled food bitter, protective Bitter – most poisons and spoiled food bitter, protective

Factors of Taste Temperature, texture Temperature, texture Spicy food excites pain receptors in mouth Spicy food excites pain receptors in mouth Taste and Smell Complementary Taste and Smell Complementary Eating when you have cold 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 Beginning in 60’s ability to taste and smell diminishes Decrease in # of receptors Decrease in # of receptors About 50% over 80 cannot smell About 50% over 80 cannot smell Sense of taste is poor Sense of taste is poor

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

Impact of LOSS Quality of life, often leading to decreased appetite and poor nutrition Quality of life, often leading to decreased appetite and poor nutrition Contributes to depression 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 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

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