Chemical senses Flashcards
Where are taste perceived?
Tongue
Palate - taste buds present
Epiglottis - taste buds present
Pharynx and nasal cavity - odour detected by olfactory receptors
What is the taste transduction mechanism for saltiness?
Na+ passes through Na+ selective channels
Depolarisation, activation of VGCC
Vesicular release of neurotransmitter is elicited and gustatory afferents activated
Special Na+ selective channel used to detect low concentration of salt, generally stay open as its insensitive to voltage
What is the taste transduction mechanism for sourness?
H+ can pass through proton channels and bind to block K+ selective channels
Leading to depolarisation of the taste cell, activating VGSC and VGCCs
Vesicular release of neurotransmitter is elicited and gustatory afferents actived
Which GPCR are responsible for which taste?
Bitter - T2Rs
Sweet - T1R2 + T1R3
Umami - T1R1 + T1R3
What is the taste transduction mechanism for bitterness?
Bitter tastants bind to T2R which is Gq coupled
PLC - PIP2 → GAG + IP3 = Ca2+ release due to Na+ ion channel activation = depolarisation
Leading to ATP release and gustatory afferents are activated
What is the taste transduction mechanism for sweetness?
Sweet tastants bind to dimer receptor formed from T1R2 and T1R3
Gq, the same as bitterness
What is the taste transduction mechanisms for umami
Umami tastants bind to dimer receptor formed from T1R1 and T1R3 which is Gq
same as bitterness and sweetness
Why do we not confuse bitter, sweet and umami tastes?
Taste cells express either bitter, sweet or umami receptors and connect to different gustatory axons
What is the flow of taste information to the CNS?
Taste cells to gustatory axons to gustatory uncleus (medulla) to ventral posterior medial nucleus (thalamus) and to the gustatory cortex
What 3 main cells make up the olfactory epithelium?
Olfactory receptor cell - site of transduction
Supporting cells - produce mucus so that odorants dissolve on mucus layer before contacting cilia of olfactory receptor cells
Basal cells - immature olfactory receptor cells able to differentiate into mature olfactory receptor cells
What is the olfactory transduction mechanism
Odrant molecules bind to odorant receptor proteins on cilia
Olfactory-specific G-protein (Golf) is activated
AC activation, increases cAMP formation
cAMP-activated channels open, allowing Na+ & Ca2+ influx
Ca2+ activate Cl- channel for Cl- efflux
causes membrane depolarisation of the olfactory neuron
What is the flow of smell information to the CNS?
Olfactory receptor cells send axons into olfactory bulb
same protein receptors project into the same glomeruli of the bulb
signals are relayed in the bulb to:
frontal cortex - concious preception of smell
hypothalamus amygdala - motivational and emotional aspects of smell
hippocampus - odour memory
What is population coding for gustation & olfaction?
Response from the combination of receptor proteins allows for the brain to distinguish odour
