Special Senses: Hearing, Taste, Smell

Special Senses: Hearing, Taste, Smell Chapter 8

Agenda • Anatomy of the Ear • Equilibrium • Hearing • Olfactory Receptors • Taste

The Ear: Hearing and Balance • Two functions: Hearing and Balance • Fluid must be stirred to stimulate receptors • Hearing: Sound vibrations • Equilibrium: Gross movements • Mechanoreceptors: respond to physical forces • Both respond to different stimuli and activated separately

Anatomy of Ear • Divided into 3 regions: External, Middle, Internal • External Ear • Auricle and Auditory Canal • Ceruminous Glands in canal secrete earwax • Tympanic membrane - eardrum

Anatomy of Ear • Middle Ear • Tympanic Cavity – air filled, mucosa-lined • Eardrum and bony wall • Eustachian Tube – connects to throat • Equalize Pressure for free movement of eardrum • Ossicles – hammer, anvil, stirrup

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 • Filled with plasma like fluid – perilymph • Membranous labyrinth – filled with endolymph

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 is Basilar Membrane, hairs bent by Tectorial membrane • Transmitted to Cochlear nerve Figure 8.15

Hearing • Hear “in-stereo” • Auditory receptors adapt • Last sense to leave, first to return

Diseases of the Ear • Deafness – hearing loss of any degree • Conduction – temp or perm loss due to physical interference with sound conduction. • Mechanical problem • Hearing aids can help, use skull bones, air conducted sound • Sensorineural – degeneration or damage to receptor cells in spiral organ of Corti, cochlear nerve, or nerves of auditory cortex • Problem of nervous system structures

Equilibrium • Sense responds to head movements • Equilibrium Receptors - Vestibular Apparatus 2 functions • Monitor Static Equilibrium • Dynamic Equilibrium

Static Equilibrium • Within membrane sacs of vestibule are maculae • Maculae detect change in head position with respect to gravity when holding still • Responsible for sense of up or down, head erect Figure 8.13

Dynamic Equilibrium • Receptors found in semicircular canals • Respond to angular or rotatory movements • Oriented in 3 planes • Ampulla, Crista Ampullaris, Cupula • Movement constant rate, adapts • Both types of receptors, sight, muscles all imp. balance Figure 8.14

Meniere’s Syndrome • Suspected causes – arteriosclerosis, degeneration of cranial nerves, increased pressure of inner ear fluids • Progressive deafness occurs • Nauseated, howling or ringing sounds, vertigo • Anti-motion sickness pills

Presbycusis • Gradual deterioration of spiral organ of Corti • Type of sensorineural deafness • More common in elderly, but seeing more in young due to loud world • Hearing loss is progressive and cumulative

Chemical Senses: Taste and Smell • Chemoreceptor – respond to chemicals in solution • Five types of receptors for taste • Olfactory receptors much more sensitive • Complement each other, respond to same stimuli

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

Anosmias • Olfactory disorder – loss of chemical sense • Due to head injuries, aftermath of nasal inflammation, aging • Brain disorders can destroy or mimic smell • Olfactory auras – epileptics

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 • Gustatory cells – respond to chemicals • Gustatory hairs – microvilli, protrude through taste pore • Stimulated, depolarize, impulses transmitted to brain • Dynamic cells, replaced every 7-10 days by basal cells Figure 8.18

Five Taste Sensations • Sweet – sugars, saccharine, some a.a., lead salts • 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

Special Senses: Hearing, Taste, Smell