Lecture 7: Gustation and olfaction

Question 1

What is flavour?

Answer 1

the sensory experience of food and drink and is dominated by smell and taste but includes texture, appearance, temperature, pain (chilli) and fat

Question 2

What are the five defined tastes?

Answer 2

salt, sweet, umami, sour and bitter

also have fat, heat (chilli, mustard, pepper), kokumi (mouth feel, a flavour)

Question 3

How many different odours can humans detect?

Answer 3

more than 2,000

none are tastes

Question 4

What can food/drink activate in the mouth?

Answer 4

taste (gustatory) afferents and olfactory afferents

Question 5

How is olfaction detected?

Answer 5

via diffusion of volatile odourants into the nasal cavity

Question 6

How are taste signals transmitted to the brain?

Answer 6

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

Question 7

What happens when a NT is released from a taste cell?

Answer 7

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

Question 8

What is a significant difference smell has to all other sensations?

Answer 8

smell doesn’t have to be processed in the thalamus

Question 9

What are the different types of taste cell and what do they detect?

Answer 9

type I TRCs (low salt conc.), type II TRCs (sweet, umami, bitter and kokumi?) and type III TRCs (sour acids)

Question 10

What do different types of TRCs express?

Answer 10

different receptors

Question 11

How does transduction differ between taste cells?

Answer 11

transduction can be simple (TRC1), via G-protein coupled receptors (TRC2) or via otopetrin-1 (TRC3)

Question 12

What does each of the different tastes activate?

Answer 12

a different type of receptor group

Question 13

How are NTs released from the taste cell? What is the transmitter likely to be?

Answer 13

release mechanism not via conventional vesicle exocytosis

ATP acting via ionotropic P2X2/P2X3 receptors

Question 14

What does the depolarisation of a taste cell result in?

Answer 14

releases ATP which depolarises gustatory afferent terminals

Question 15

Which NTs alter signals in the taste pathway?

Answer 15

serotonin, GABA, acetylcholine, noradrenaline and glutamate

Question 16

Where is the olfactory epithelium and what does it contain?

Answer 16

on the roof of the nasal cavity and contains olfactory receptor cells (neurons) that turn over continuously

Question 17

Where do olfactory receptor cells send axons to?

Answer 17

through Cribiform plate to the olfactory bulb

Question 18

What does selectivity depend on in olfactory transduction?

Answer 18

depends on the odourant receptor molecule

pathway is common after the activation of the receptor

Question 19

What do different olfactory neurons have?

Answer 19

different response profiles to arrays of odourants

profile determines “receptive field”

Question 20

What is the structure of the olfactory bulb?

Answer 20

second order olfactory neurons have branching dendritic trees that form glomeruli with terminals of olfactory receptor cells

Question 21

What do granule cell neurons act as?

Answer 21

tuning interneurons

Question 22

What do individual glomeruli encode?

Answer 22

only one odour

Question 23

What do receptors cells that synapse on a particular glomerulus all have?

Answer 23

the same receptive field (express the same odourant receptor)

Question 24

Where do neurons of the olfactory bulb project?

Answer 24

directly to olfactory cortex and then to thalamus

also have projection via olfactory tubercle to medial dorsal thalamus and then orbitofrontal cortex

Question 25

What are the central olfactory pathways integrated with?

Answer 25

mood and affect via amygdala