Touch, Taste, Smell

Chemoreceptors Pain receptors Thermoreceptors Mechanoreceptors Smell and taste Pain receptors touch Thermoreceptors Taste and touch Mechanoreceptors Hearing (proprioreceptors)

Dermal Structures Receptors Location Function Bare nerve endings Meissner’s corpuscles Pacinian corpuscles Merkel’s Disks Ruffini’s corpuscles

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)

Sensory impulses are analyzed within olfactory bulbs. 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 Burning Sensation 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 spherical Taste pore 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

Chemicals dissolve in saliva 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