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MODULE 12-A&P 1.docx - MODULE 12 Module Objectives: Upon...

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MODULE 12Module Objectives:Upon completion of this module, the student will be able to:Describe the structure and function of the eye and accessory eyestructures.Trace the pathway of light through the eye to the retina, and explainhow light is focused for distant and close vision.Describe the events involved in the stimulation of photoreceptors bylight, and compare and contrast the roles of rods and cones in vision.Trace the visual pathway to the visual cortex, and briefly describethe steps in visual processing.Describe the location, structure, and afferent pathways of taste andsmell receptors, and explain how these receptors are activated.Describe the sound conduction pathway to the fluids of the internalear, and follow the auditory pathway from the spiral organ (of Corti) to thetemporal cortex.Explain how the balance organs of the semicircular canals and thevestibule help maintain dynamic and static equilibriumIntroduction to the Special SensesThe special senses include vision, audition (hearing), equilibrium(balance), gustation (taste), and olfaction (smell). Special senses aredistinguished from the somatosensory modalities in that they have aspecific organ dedicated to them, namely the eye, the ear, the tongue,and the nose. Sensory receptors for the tongue and the nose arechemoreceptors, those for the ear are mechanoreceptors, and the eyeutilizes photoreceptors.Chemical SensationsGustation (taste):The tongue is covered by stratified squamous epithelium. Raised bumpscalledpapillaecontain taste buds. Within the taste buds are specializedgustatory receptor cells that respond to chemicals in the ingested food.There are five recognized tastes, to which the gustatory receptor cellsrespond. These include sweet, salty, sour, bitter, and umami (savory,meaty). When the various tastes are present in food, the gustatoryreceptor cells release neurotransmitters based on the amount of thechemical in the food. Once activated, the gustatory receptor cells can
MODULE 12stimulate sensory neurons in the glossopharyngeal, vagus, and facialnerves. These cranial nerves then transmit the information to the cortex.Salty taste is transmitted when the ingested food contains high amountsof NaCl that dissociates in the saliva. The Na+ then enters the gustatoryreceptor cells causing depolarization and activation. Likewise, sour tasteresponds to H+ in the food, which enters the gustatory receptor cells tocause depolarization and activation.The remaining tastes work through second messenger systems using G-proteins. For example, sugars bind to receptors on the gustatory receptorcells that utilize G-proteins to activate second messengers, whichultimately lead to depolarization of the cells. Umami taste is perceivedwhen the amino acid L-glutamate is present in food and binds to itsspecific G-protein coupled receptor. Bitter taste is the most variablebecause in some cases bitter chemicals can depolarize gustatory receptor

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Term
Fall
Professor
Kris Amatuli
Tags
Physiology, Anatomy, pigmented layer

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