Physiology of Olfaction and Gustation

Question 1

What is …
Anosmia
Aguesia

Answer 1

• loss of smell

- loss of taste

Question 2

What are the domains of the taste bud cells?

Answer 2

Taste cells are specialized epithelial cells. Apical domain has the chemosensory part that binds chemicals while basal domain has the parts that contacts afferents and makes electrical signals to send to brain

Question 3

*How does sensory transduction work in taste cells?

Answer 3

Taste receptors (like TRP) are on microvilli and bind taste molecules > depolarization > increase Ca2+ influx > vesicle release (serotonin or ATP) on basal afferents

Question 4

Sour and salty bind which ligands and release which NTs?

Answer 4

Sour binds H+ while salty binds Na+. Both release serotonin

Question 5

Sweet, umami and bitter bind which ligands and release which NTs?

Answer 5

Sweet binds sugars, umami binds glutamate and bitter binds various compounds (all are via taste specific GPCRs). All release ATP as NT

Question 6

What kind of neurons are olfactory neurons and what NT do they release?

Answer 6

Bipolar neurons. NT is glutamate

Question 7

How does the sensory transduction of olfactory neurons work?

Answer 7

Odorants bind to receptors on cilia > activation of G olf (G protein) > activation of adenylate cyclase > increase in cAMP > opens cation channel > increase in Na+ and Ca2+ > depolarization > increase in Ca2+ and Cl- > strong receptor potential > AP

Question 8

How is olfaction desensitized?

Answer 8

Two ways. Decreasing cation channel sensitivity to cAMP by Ca binding to calmodulin (thus reducing the cation influx) or phosphorylate a receptor to inactivate it.
Results in getting used to the smell

Question 9

What do these tastes indicate that’s good for the body?
Sweet
Salty
Umami

Answer 9

• presence of carbs = energy source = eat that
• oversees intake of salts for water balance and homeostasis
• presence of protein due to glutamate

Question 10

What do these tastes indicate that’s bad for the body?
Sour
Bitter

Answer 10

• aversive due to presence of dietary acids. Tells you to avoid excess acids to not disrupt acid-base balance
• aversive due to possible poisons

Question 11

How did bitter GPCRs evolve to prevent death by poison?

Answer 11

High binding affinity so that low concentrations of the bitter are enough to make you gag and not eat more

Question 12

What is the importance of decreased salt sensitivity as you age?

Answer 12

Can’t taste salt = add more salt. Older people are vulnerable due to HTN and possibly disrupting electrolyte balance by consuming more salt

Question 13

What is the relationship of sweet stuff to babies?

Answer 13

Babies are primed in utero to like sweet things. Sweet (sucrose) seems to have pleasure/analgesic effects in infants by inducing a beta endorphin system that activates the opioid system.
-Could also be related to babies needing to grow while adults don’t need to as much so there is decreased appetite for sweet as you grow older

Question 14

How do sweet/salty mask bitter tastes?

Answer 14

Sweet suppress it at the cognitive level while salty suppresses it at the level of the bitter receptor

Question 15

*What is the role of solitary tract in taste processing?

Answer 15

Receives info from viscera via vagus nerve

Responsible for taste reflexes (salivating, swallowing etc.)

Question 16

*What is the role of the VPM?

Answer 16

Relay station in the thalamus. Processes discriminative taste

Question 17

What makes up the gustatory cortex? What does it do?

Answer 17

Insula, pars opercularis and post central gyrus

-sends gustatory info to the orbitofrontal cortex

Question 18

*What roles do the hypothalamus and amygdala play in taste processing?

Answer 18

Hypothalamus = relates food with homeostatic/physiological stuff (e.g. hunger)
Amygdala = emotional parts as well as memories of eating

Question 19

*What role does the orbitofrontal cortex play in taste processing?

Answer 19

Puts all the input together from all senses to collectively appreciate food (flavor)

Question 20

*What does the anterior olfactory nucleus do in olfaction processing?

Answer 20

Relay station to ipsilateral and contralateral cortices

Question 21

*What does the piriform cortex and lateral hypothalamus do in olfaction processing?

Answer 21

Appetite control using olfactory input

Question 22

*What does the piriform cortex and medial orbitofrontal cortex do in olfaction processing?

Answer 22

Integration of the sight, smell and taste of food (flavor appreciation)

Question 23

*What does the anterior cortical amygdaloid nuclei do in olfaction processing?

Answer 23

Emotional learning and fear conditioning via olfaction

Question 24

*What does the periamygdaloid cortex do in olfaction processing?

Answer 24

Integrates emotional aspects of food from odor

Question 25

*What does the entorhinal cortex and hippocampus do in olfaction processing?

Answer 25

Memory and recall upon odor sensation

Question 26

Neurodegenerative diseases and olfaction

Answer 26

Olfaction impairment is common in neurodegenerative diseases like Parkinsons (first to be defective)