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Touch, Taste, Smell • Chemoreceptors – Smell and taste • Pain receptors – touch • Thermoreceptors – Taste and touch • Mechanoreceptors – Hearing (proprioreceptors) Dermal Structures Receptors Bare nerve endings Meissner’s corpuscles Pacinian corpuscles Merkel’s Disks Ruffini’s corpuscles Location Function Pain Receptors • Provide protection • Do not adapt rapidly • Stimulated by – Changes in temperature – Mechanical force Smell • Olfactory organ – Appear as the yellowish mass – They are covered by a pinkish mucous membrane – Nasal cavity, superior nasal conchae, nasal septum – Contain the olfactory receptor cells (400 receptors in human) How we smell • Olfactory receptors – bipolar neurons surrounded by columnar epithelial cells – Chemoreceptor • Gas partially dissolves • Knobs at distal end of dendrites covered with hair-like cilia – Generates nerve impulse • (travel along axon through openings of cribriform plates of ethmoid bone) • fibers synapse with neurons located in the enlargement of the olfactory bulbs: – Structures that lie on either side of the crista galli of the ethmoid bone. • Sensory impulses are analyzed within olfactory bulbs. Unique characteristics • Undergo sensory adaptation rather rapidly. – intensity of an odor drops 50% within a second following the stimulation. – Within a minute may become insensitive to odor. • Only nerve cells in direct contact with the outside environment. – Subject to damage – Only damaged neurons that are regularly replaced. Taste • Saliva (must dissolve) • Combination of chemicals binding to specific receptors on taste hair surfaces • Binding results in depolarization • Degree of change is directly proportional to concentration of tasted substance Taste • 5 primary tastes – Flavors results of one (or combination of) flavor(s) on tongue • Sweet (tip) • Sour (margins) • Salty (everywhere) • Bitter (back) • Umami (unknown) – Different factors may influence taste • Temperature • Smell • Texture – Burning Sensation • Capaisin-irritant Taste Receptors • Gustatory/ taste cells – Modified epithelial cells – Function as receptors in the taste buds. – Each of our 10,000 taste buds houses 50-150 taste cells. • spherical • Taste pore – Located on the free surface, an opening where projection (microviilli) protrude • Masticate food • Chemicals dissolve in saliva • Network of nerve fibers are interwoven and wrapped around taste cells. – Ends of the fibers closely contact receptor cell membranes. – Stimulated receptor cell triggers an impulse on a nearby nerve fiber. • Facial • Glossopharyngeal • vagus nerves – Then travels to the brain. Impulses • Medulla oblongata up thalamus to gustatory cortex (parietal lobes for interpretation) • Functions for ~ 3 days then replaced • Exposed to external environment but not as high turnover as nose