Gustation Flashcards
Primary tastes
- salty; TFS = 0.01M
- sour; TFS = 0.009M
- sweet; TFS = 0.01M
- bitter; TFS = 0.000008M
- umami
Why is the threshold for stimulation of bitter taste very low
it is primarily used to detect poisons (avoid)
Role of the papillae
- help grip food while your teeth are chewing
- small buds on tongue
- contain taste buds
Components of the taste buds
- taste cell
- microvilli
- supporting cell
- connective tissue
- sensory nerve fibres
Role of the taste cell
sense various chemical compounds in foods and transmit these signals through gustatory nerve fibers to the central nervous system
Role of the taste cell
sense various chemical compounds in foods and transmit these signals through gustatory nerve fibers to the central nervous system
Organisation of taste bud
- found in papillae
- ~4000 on average, number declines with age
- each bud contains ~50-100 taste cells
- apical microvilli of taste cells are exposed to saliva through taste pore
Taste cell
- mature taste cells are short-lived and continuously regenerated from basal cells
- action potential releases NT which activates gustatory afferent fibre
How are substances sensed
- at microvilli
- induces depolarisation and AP generation
Salty transduction
- satly-sensing taste cells express amiloride-sensitive sodium channels (ENaC)
- sodium enters through channel to depolarise cell
- potassium-type salts also stimulate cells because of leak potassium channels and change in EK
Sour transduction
- sour-sensing taste cells express proton-sensitive potassium leak channels
- sour is the taste of acid (H+)
- Acid protons block potassium channels, reducing aK and depolarising cell
- newly discovered acid-sensing cation channel gated by H+
Bitter transduction
- bitter-sensing taste cells use 7-TM receptors coupled to various G proteins
- recognises toxic compounds
- family of related bitter receptors (T2 receptors)
- some receptors couple to Gq which activates PLC to increase Ca2+ through IP3
- other receptors couple to gustducin which activates cyclic nucleotide phosphodiesterases
- few bitter compounds block leak potassium channels
Sweet transduction
- sweet-sensing taste cells use 7-TM receptor coupled to Gs
- sugars act through Gs to produce cAMP
- PKA phosphorylates and closes K leak channels (depolarisation)
Sweet transduction
- sweet-sensing taste cells use 7-TM receptor coupled to Gs
- sugars act through Gs to produce cAMP
- PKA phosphorylates and closes K leak channels (depolarisation)
Transduction of artificial sweeteners
- bind receptors coupled to Gq which activates PLC to increase Ca2+ through IP3
Transduction pathway
- ligands activate the taste cell
- multiple intracellular pathways are activated
- Ca2+ signal in the cytoplasm triggers exocytosis
- neurotransmitter is released and primary sensory neuron fired
- APs are sent to the brain
Coding of taste
- pattern of activation of different taste receptors provide complexity in taste
- non congruent with label-line principle
Labelled line
stimulus will activate one specific receptor, which will activate only one specific pathway to the CNS (not happening in reality)
Pattern code
stimulus will activate all receptors in different manners and proportions, then CNS decodes the signal
Intensity of taste
taste cell neurons increase firing rate with increases in stimulus concentration (mmol)
Orbital frontal cortex (OFC)
- responses from taste and smell are first combined
- recieves input from primary somatosensory cortex and inferotemporal cortex
Role of bimodal neurons in inferotemporal cortex
- respond to taste and smell as well as taste and vision
- firing of these neurons is affected by the level of hunger of the animal for a specific food
