olfaction (smell) & gustation (taste)

olfaction

detection of airborne molecules called “odorants”

how many odorants can humans distinguish

~1 trillion odorants

odorants are detected by

cells called olfactory receptor cells, which live ~2 months before being replaced

for olfaction mucus serves to

moisten & clean air, keeps olfactory receptor cells from drying out, contains antibodies to fight foreign invaders, transports odorants, degrades odorants over time

how many olfactory receptor cells do humans have

~10 million; each one makes slightly diff type of odorant receptor for the membrane of its dendrites

how much mucus is produced per day

~1.5 liters

mucus

is swept to the back of the throat, where its swallowed & kills any foreign invaders

newly made mucus

takes ~10 minutes to be swept to back of throat & swallowed

the brain can localize smell

by comparing intensity of smell in left & right nostril

gustation

detection of molecules dissolved in the saliva

where does gustation take place

mostly on the tongue, but some in back of throat

papilla

“bumps” on tongue; house taste buds

5 basic tastes

salty, sour, sweet, bitter, savory

salty

detection of sodium (Na+) ions

sour

detection of H+ ions (acid)

sweet

detections of small sugars (glucose)

bitter

detection of bitter molecules

savory (umami)

detection of amino acids & nucleotides

basic tastes

have their own unique transduction pathway