Taste Flashcards
Stimulus of Taste
chemicals sensed by chemoreceptors
Where are taste receptors?
tongue, palate, pharynx and epiglottis
Papillae
folds in epithelium
Sweet stimulus
sugar
Sour stimulus
acid
Salty stimulus
sodium (NaCl)
Bitter stimulus
alkaloids (e.g. coffee)
Umami stimulus
amino acids - especially glutamate
How many cells in a taste bud?
50-100 columnar epithelial cells (type I, II and III)
What tastes activate Type I receptors?
not involved in taste, help to maintain homeostasis of the taste bud
What tastes activate Type II receptors?
sweet, bitter and umami
What tastes activate Type III receptors?
sour and salty
What happens after tastant interacts with receptor?
Ca2+ influx into the cell
What does Ca2+ influx cause?
Release of neurotransmitter or signalling molecule that interacts with an afferent nerve fibre
Transduction Mechanism neurotransmitters (4)
ATP
GABA
Serotonin
Ach
Type II taste cell G-protein mediated signalling
Gq protein pathway: phospholipase C
Sugar receptor
Type I homodimer
on Type II cell
Umami receptor
Type I heterodimer (on Type II cell)
Bitter receptor
Type II monomer (on Type II cell)
Otop1
Sour
ENaC
Salt
Capsaicin
Active componant of chillis
Piperine
alkaloid that gives pepper its pungency
Astringent foods
High amounts of tannins, causes contraction of mucus layers in mouth leaving mouth dry
- popcorn, unripened bananas, pomegranates
CD36
fatty acid receptor
Sour transduction pathway
When an acid interacts with a type III taste cell, proton influx via OTOP 1, pH decreases (more acidic)depolarises cell, blocks the leaky K+ channel and stops K+ from leaving, leading to depolarisation, opening voltage gated Na+ channel, influx of Na+ leading to an action potential, which opens the Ca2+ channels and we get an influx of Ca2+, which leads to the release of vesicles containing neurotransmitters to be released onto afferent nerve fibres
Salt transduction pathway
Na enters cells through ENaC ( Epithelial Sodium Channel) causing depolarisation, opening voltage gated calcium channels, Ca comes in and cause release of neurotransmitters onto afferent nerve fibres
Taste bud innervation (4)
Chorda tympani
Lingual
Trigeminal
Glossopharyngeal
Motor nerve to tongue muscle isn mainly:
Hypoglossal
Taste signal transduction pathway
Afferent fibres -> medulla -> thalamus -> cortex
Aguesia
Total loss of taste
Dysguesia
Persistent horrible taste in mouth
Hyperguesia
Partial loss of one type of taste
What causes a decrease in pH / influx of protons into Type III sour receptor cells?
Acid interaction / sour
What does a decrease in pH in /influx of protons into Type III receptor cells result in?
Blocking of leaky K+ channels
What happens when leaky K+ channels are blocked?
Depolarisation of cell
What happens when the cell depolarises from blocking K+ channels?
Opens Na+ channels
What does the opening of Na+ channels cause?
Firing of action potentials and opening of Ca2+ channels
Which cells are G-protein mediated?
Type II taste cells
