Lecture 7: Gustation and olfaction Flashcards
What is flavour?
the sensory experience of food and drink and is dominated by smell and taste but includes texture, appearance, temperature, pain (chilli) and fat
What are the five defined tastes?
salt, sweet, umami, sour and bitter
also have fat, heat (chilli, mustard, pepper), kokumi (mouth feel, a flavour)
How many different odours can humans detect?
more than 2,000
none are tastes
What can food/drink activate in the mouth?
taste (gustatory) afferents and olfactory afferents
How is olfaction detected?
via diffusion of volatile odourants into the nasal cavity
How are taste signals transmitted to the brain?
food particles activate GPCRs present on taste cells
upon activation a G protein dissociates and undergoes intracellular pathways which result in an increase in internal calcium which in turn leads to the release of a NT
What happens when a NT is released from a taste cell?
activates afferent sensory nerve fibres which run in cranial nerves VII, IX and X up into a region of the brain called the nucleus soltarius in medulla and from there axons run to the thalamus and from there different axons run into the gustatory cortex
What is a significant difference smell has to all other sensations?
smell doesn’t have to be processed in the thalamus
What are the different types of taste cell and what do they detect?
type I TRCs (low salt conc.), type II TRCs (sweet, umami, bitter and kokumi?) and type III TRCs (sour acids)
What do different types of TRCs express?
different receptors
How does transduction differ between taste cells?
transduction can be simple (TRC1), via G-protein coupled receptors (TRC2) or via otopetrin-1 (TRC3)
What does each of the different tastes activate?
a different type of receptor group
How are NTs released from the taste cell? What is the transmitter likely to be?
release mechanism not via conventional vesicle exocytosis
ATP acting via ionotropic P2X2/P2X3 receptors
What does the depolarisation of a taste cell result in?
releases ATP which depolarises gustatory afferent terminals
Which NTs alter signals in the taste pathway?
serotonin, GABA, acetylcholine, noradrenaline and glutamate
Where is the olfactory epithelium and what does it contain?
on the roof of the nasal cavity and contains olfactory receptor cells (neurons) that turn over continuously
Where do olfactory receptor cells send axons to?
through Cribiform plate to the olfactory bulb
What does selectivity depend on in olfactory transduction?
depends on the odourant receptor molecule
pathway is common after the activation of the receptor
What do different olfactory neurons have?
different response profiles to arrays of odourants
profile determines “receptive field”
What is the structure of the olfactory bulb?
second order olfactory neurons have branching dendritic trees that form glomeruli with terminals of olfactory receptor cells
What do granule cell neurons act as?
tuning interneurons
What do individual glomeruli encode?
only one odour
What do receptors cells that synapse on a particular glomerulus all have?
the same receptive field (express the same odourant receptor)
Where do neurons of the olfactory bulb project?
directly to olfactory cortex and then to thalamus
also have projection via olfactory tubercle to medial dorsal thalamus and then orbitofrontal cortex
