taste

tastants

salty, sweet, sour, bitter, umami

taste buds

located on sides of taste pores

between papillae

Circumvallate papillae

back of tongue

Foliate papillae

sides of tongue

Fungiform papillae

front of tongue

Cranial Nerves

bundles of nerves that emerge from brain, controls sensory and motor processing

vagus nerve

Known as the "wandering" nerve, it regulates involuntary motor control of the heart, lungs, and digestive tract, and provides sensory input to the epiglottis/larynx

glossopharyngeal nerve

Primarily provides sensory input (taste and general) to the posterior 1/3 of the tongue, controls the pharynx for swallowing, and supplies the parotid gland.

Facial nerve

Primarily controls muscles of facial expression, taste on the anterior 2/3 of the tongue, and secretion from salivary/lacrimal glands.

taste cells

located within taste buds on the tongue, palate, and throat that detect five basic tastes: sweet, sour, salty, bitter, and umami (not neurons), replaced every 10-14 days - can respond to bitter toxins, protective reflex in airway, and preserve fertility

Transduction

1. Tastant binds to receptor on cilia

2. receptor activation produces receptor potential (like EPSPs, not AP, causing neurotransmitter release)

3. neurotransmitters release onto Glassopharyngeal,Facial, and Vagus cranial nerves, causing AP

4. travels to Thalamus, then cortex

gustatopic map

Distinct neurons are clustered into segregated "hot spots" for each of the five basic tastes: sweet, bitter, umami, salty, and sour

Salty

1. Na ion enter taste cells thru open ion channels in membrane

2. causes depolarization

3. TRPV1 may also contribute

-low concentrations = appetizing and high concentrations = unpalatable

Sour

• acidic solution = sour = H+

-protons enter thru selective ion channel, OTOP1, causing depolarization

• K+ channels blocked, preventing K+ from leaving cell, further depolarizing

Sweet

• binds to T1R2 + T1R3, causing them to dimerize

• activates G protein

• second messenger cascade

• triggers Ca 2+ to taste cells

• receptor potential = neurotransmitter release

Umami

• amino acid binds to heterodimer T1R1 and T1R3

• variant of metabotropic glutamate receptor (activated by L-glutamate and monosodium glutamate)

Bitter

• T2R receptors

• 30 different T2Rs, allows for detection of many bitter components

• protects from spoiled food

Taste receptor pathway

• receptor potentials release neurotransmitters from tastants

• cranial nerves carry AP from taste cells to brainstem (integrates taste info)

• Thalamus (VPM) relays taste signals to gustatory cortex