Lecture 4: Physiology of Olfaction and Gustation

Question 1

What is anosmia?

Answer 1

Loss of smell

Question 2

What is aguesia?

Answer 2

Loss of taste

Question 3

What tastants trigger the release of serotonin?

Answer 3

Sour and salty

Conventional calcium-triggered release

Question 4

What tastants trigger the release of ATP?

Answer 4

Sweet, umami, and bitter

(SUB sandwiches give you energy)

Calcium triggered release of ATP

Question 5

What stimutas sour tastant?

What does it recognize?

Answer 5

Hydrogen Ions

Presence of dietary acids (can be found in spoiled foods)

Question 6

What stimulates salty tastant?

Answer 6

Na+ binding ENaC

Question 7

What stimulates sweet tastant?

What can it recognize?

Answer 7

Sugars binding GPCRs

Presence of carbohydrates that serve as energy sourse

Question 8

What stimulates umami tastant?

What does it recognize?

Answer 8

Glutamate binding mGluR4 (GPCR)

Food’s protein content due to presence of glutamate

Question 9

What stimulates bitter tastant?

Answer 9

Various compounds binding GPCRs

Question 10

Which tastant binds its GPCR with very high binding affinity?

Answer 10

Bitter (avoid poison)

Question 11

What type of cells are olfactory cells and what NT does it release?

Answer 11

Bipolar Neurons that release glutamate

Question 12

What is activated by the G-olf GPCR pathway?

Answer 12

Adenylyl Cyclase III which increases cAMP, activating CNGC

Question 13

What happens when CNGC channels are open?

Answer 13

Cation influx, resulting in depolarization and opening of a calcium-gated Cl- channel

Question 14

What are the two main ways that adaptation to odorant stimulation occurs?

Answer 14

1. Sensitivity of CNGC to cAMP decreases –> decreased cation influx –> decreased depolarization
2. Inactivation by receptor phosphorylation

Question 15

What happpens to gustatory and olfactory sensitivity with age?

Answer 15

Decreases

Why you can tolerate more salt and spices as you are older

Question 16

What activates the endogenous opioid system?

Answer 16

Sweet-tasted induced beta-endorphin release

Question 17

How is bitter taste in medicine blocked?

Answer 17

Sodium salts can sppress bitter taste at receptor

Question 18

Where do the afferent neurons (1^st order) coming from the taste buds terminate?

Answer 18

Nucleus Tractus Solitarius (gustatory area)

Receives multiple sensory inputs

Question 19

In the ascending taste pathway, where do the 2nd order sensory neuron cell bodies arise?

Where do they terminate?

Answer 19

Arise from nucleus tractus solitarius

Terminate in VPM nucleus of thalamus

Question 20

What is the role of the ventral posterior medal nucleus of thalamus?

Answer 20

Identifying the discriminative aspects of taste

Question 21

Where do the 3rd order neurons of the ascending taste pathway arise?

Where do they terminate?

Answer 21

Arise from VPM and travel through Posterior Limb of IC

Terminate in Gustatory Cortex

• Insular Taste Cortex
• Operculum of Frontal Cortex
• Postcentral Gyrus

Question 22

What role does the hypothalamus and amygdala play with taste?

Answer 22

Emotional context to eating and memories of eating

Role in hunger

Question 23

What role does the orbitofrontal cortex have in the taste pathway?

Answer 23

Interpretation of taste, olfaction, and visual cues regarding food

Appreciation of flavor, food reward, control of feeding

Question 24

How do olfactory receptor neurons relay information to olfactory tract?

Answer 24

1. Olfactory neurons synapse onto glomeruli cells and release GABA + glutamate
2. Local interneurons release GABA to increase specificity of signal
3. Mitral and tufted cells will project to olfactory tract
4. Granular cells release GABA to increase specificity again

Question 25

What is the anterior olfactory nucleus?

Answer 25

Relay station to ipsilateral and contralateral cortices

Poorly understood

Question 26

What is the function of the piriform cortex and lateral hypothalmus?

Answer 26

Control of appetite

How olfactory input influences appetite and hunger

Question 27

What is the function of the piriform cortex and medial orbitofrontal cortex?

Answer 27

Integration of sight, smell, and taste of food

Appreciation of the flavor of food

Question 28

What is the function of the anterior cortical amygdaloid nuclei?

Answer 28

Emotional learning

Olfactory fear conditioning

Question 29

What is the function of the periamygdaloid cortex?

Answer 29

Integration of the emotional aspect of food as elicited by odor

More about response

Question 30

What is the function of the entorhinal cortex and hippocampus?

Answer 30

• Memory formation and how olfactory input facilitates both memory and recall
• Connections within the limbic system and entorhinal cortex are responsible for the highly evocative experience of memory upon odor sensation.