L10 - Gustation & Olfaction

Question 1

5 sensory stimuli and 1 new one is

Answer 1

Acid, bitter, sweet, salt, umami (MSG) AND fatty acid

Question 2

Where are fatty acid receptors found in mouth

Answer 2

in palate, upper part roof of mouth

Question 3

Why is fat so delicious?

Answer 3

Odorants are dissolved into fats - Olfaction via diffusion of volatie odorants into nasal cavity

Question 4

Where are taste buds found?

Answer 4

In papilae

Question 5

How long do taste cells and olfactory cells take to turn over (make new cells)?

Answer 5

2 weeks

Question 6

T/F: Taste cells in a single taste bud have different sensitivites

Answer 6

True

Question 7

Tip of tongue is used for which taste

Answer 7

Sweet

Question 8

How do the 5 sensory stimuli depolarise taste cell

Answer 8

Salt - Na+ ions depolarize taste cell via amiloride sensitive Na channels

Acid - H+ ions depolarize via H+ channels

Sweet, Umami and Bitter (G-protein coupled) - alpha-gustducin (G-protein to phospholipase C and hence to depolarising mechanisms (IP3 -> Ca2+)
*TRPM5 channel (menthol receptor that allows Ca2+ influx as well - related to capsaicin)

Question 9

Specifics about sweet, umami, bitter receptors

Answer 9

Sweet and Umami have > 1 receptor

• each operate via a heterodimer receptor
• Sweet (T1R2/T1R3)
• Umami (T1R1/T1R3) - these receptors respond to glutamate, enhanced by inosine

Bitter (T2R - taste number 2 receptor)

Question 10

Pannexin channel?

Answer 10

Recent argument that release is not via vesicle release but through this channels that opens gaps in the cytoplasm to allow NT to go into extracell. space

Question 11

List of taste cell transmitters

Answer 11

Serotonin, glutamate, ACh, Noradrenaline, GABA (usually inhibitory but excitatory in these cells), ATP

Question 12

Where do gustatory afferents synpase?

Answer 12

In gustatory nucleus, part of solitary nucleus of medulla (ipsilateral projection)

Question 13

Central taste pathways

Answer 13

Perception mediated via gustatory projection to ventral posterior medial nucleus of thalamus -> primary gustatory cortex (insula and frontal operculum)

Question 14

Where is the olfactory epithelium found?

Answer 14

On roof of nasal cavity

Question 15

Whats different from olfactory receptor cells and taste cells turn over?

Answer 15

Olfactory receptor cells have the same rate of turn over but olfactory receptor cells send axons through Cribiform plate to the olfactory bulb

Question 16

Olfactory transduction

Answer 16

G-protein coupled receptor (G olf/ alpha - transducin) a trimer -> activated by odorant -> increase cAMP in cell -> acts on cAMP dependent Na+ channel -> depolarization

Also lets Ca2+ in -> activating Cl channel -> Cl- exit cell -> depolarizing it

Question 17

Where are the olfactory receptors found?

Answer 17

On the cillia

Question 18

In a current trace, a downward deflection = ___, voltage trace is opposite

Answer 18

Depolarization

Question 19

Does specifity of odor detected occur in olfactory bulb or cortex?

Answer 19

Bulb

Question 20

Structure of olfactory bulb

Answer 20

Projection neurons (1 class called mitral cell) are second order olfactory neurons that have branching dendritic trees that form glomeruli with terminals of olfactory receptor cells. Individual glomeruli encode only one odour. Granule cell neurons (similar to amacrine cells in visual system) act as tuning interneurons that leads to output.

Question 21

T/F: Individual glomeruli encode only one odour.

Answer 21

True

Question 22

T/F: Receptor cells that synapse on a particular glomerulus all have the same receptive field (express the same odorant receptor)

Answer 22

True

Question 23

Central olfactory pathways

Answer 23

Olfactory receptors -> olfactory nerve -> Projection neurons of olfactory bulb -> olfactory tract -> olfactory bulb targets (Pyriform cortex, olfactory tubercle, amygdala, entorhinal cortex) -> Orbitofrontal cortex, thalamus, hypothalamus, hippocampal formation