Gustatory System Flashcards
what are the 4+1 primary tastes?
salty, sweet, sour, bitter and umami.
what are the thresholds for the different tastes?
salty - 0.01M
sour - 0.009M
sweet - 0.01M
bitter - 0.000008M
bitter is so low so doesn’t require a lot to taste it. this is because of our evolutionary ability to detect poisons and indicates when we should avoid eating something.
how does the anatomy of the tongue allow for taste?
there are grooves in the tongue.
chemicals generating taste mixes with saliva that moves into grooves and goes into contact with taste buds.
they have microvilli that move out of supporting structure and chemicals that generate taste sensation and come into contact with microvilli which is where the receptors are.
describe how the tastebud tastes
people have different numbers of taste buds. the number of taste cells decrease as you get older. taste cells are the only sensory cell that generate action potentials. they will generate APs and neurotransmitters are released. there are different sensory afferents that synapse with taste cells. taste cells release glutamate allowing the signal to be transmitted along fibres to the brain area responsible for sensing taste.
organisation of the taste bud
found in grove like structures called papillae.
each taste bud contains 50-100 taste cells.
mature taste cells are very short lived and are continuously regenerated from basal cells.
apical microvilli of taste cells are exposed to saliva through the taste pore.
tasty substance is sensed at microvilli and induces depolarisation and action potential generation.
taste cell action potential releases neurotransmitter which activates gustatory afferent fibre.
how is taste transduced
we can taste salt as we have an ENaC sodium channel. sodium enters cell and depolarises cell, generating AP which can be released onto afferent fibre.
sour tastes respond to protons (H+). they express proton sensitive potassium leak channels, so that sour substance is acidic meaning that H+ will be in abundance and block the K leak channel or they might gate a cation channel (Na) if they block channels there will be less potassium and cause depolarisation of cell causing AP which will release glutamate.
describe transduction mechanisms for taste modalities
ligands (e.g. salt, sweet) activate the taste cell by binding to GPCRs on the microvilli. multiple intracellular pathways are activated (e.g. K+ channel closing, Ca2+ release from intracellular stores, cell depolarisation). Ca2+ signal in the cytoplasm triggers exocytosis. neurotransmitter is release and primary sensory neuron fires. action potentials sent to the brain.
describe innervation of the tongue
vagus nerve innervates the epiglottis region of the tongue. all nerves synapse with taste cells and convey signal of taste to nucleus of solitary tract then signal travels to ventral posterior medial nucleus of thalamus which takes the signal to the primary gustatory cortex.
where is flavour perceived?
taste and smell are first combined in the orbital frontal cortex.
OFC also receives input from primary somatosensory cortex and inferotemporal cortex in visual pathways.
