Touch, Taste, Smell

• Chemoreceptors– Smell and taste

• Pain receptors– touch

• Thermoreceptors– Taste and touch

• Mechanoreceptors– Hearing

(proprioreceptors)

Dermal StructuresReceptors 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)

• 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