Ch.8 The Chemical Senses

Receptor cells

receive inputs for different senses. they themselves have receptor subunits on their cells. *different from traditional receptors

Chemical senses

refers to taste and smell b/c of chemical messengers that bind to chemoreceptors on receptor cells

Taste

gustation

Sweet

ensures enough intake of carbs for energy in the body

Sour

prevents intake of toxic substances, also detects ripeness

Salty

ensures enough intake of salt to regulate the amount of water

Bitter

prevents intake of poisonous substances

Umami

ensures enough intake of proteins for proper growth and maintenance

Papillae

small projections on tongue that contain 1-100s of taste buds

Taste buds

each contain 50-100 taste receptor cells

Receptor potential

when a chemical activates a taste receptor, its membrane potential changes, like a graded potential

If receptor potential reaches threshold concentration,

it triggers voltage-gated Ca2+ to open, triggering neurotransmitter release

Sour relases

serotonin

Salty, sweet, bitter, and umami release

ATP

Specialists

respond exclusively to 1 of 5 basic tastes

Generalists

respond to 2 or more basic tastes

Transduction

process where an environmental stimulus causes an electrical response in a sensory receptor cell

Tastant can either…

pass directly through ion channels (salty and sour)

or bind to GPCRS and activate second messengers to open ion channels (sweet, bitter, umami)

ENaC

low concentrations of Na+ are detected by Na+ selective channels

it is blocked by amiloride, is concentration-dependent, and voltage-independent

High concentrations of Na+

activate bitter and sour taste cells, leading to avoidance behavior

Salty pathway

Na+ enters via ENaC → membrane depolarizes → stimulates Ca2+ entering the cell → stimulates release of serotonin-filled synaptic vesicles → gustatory afferent axon

Sour pathway

H+ ions detected by OTOP1 → H+ ions appear to block K+ selective channels from either inside or outside the cell → membrane depolarizes → stimulates release of serotonin-filled synaptic vesicles → gustatory afferent axon