Physiology of Taste and Smell

Question 1

What occurs when taste receptors are signalled?

Answer 1

usually depolarizing –> opens voltage-gated Ca channels –> NT release

Question 2

What NT do Sour and Salty taste receptors release and what does it signal?

Answer 2

Serotonin –> post-syn primary gustatory neurons

Question 3

What NT do Sweet, Bitter, and Umami receptors release and what does that stimulate?

Answer 3

(these things give you energy)

ATP –> post-syn primary gustatory neurons

or pre-synaptic salty/sour recptor cells –> 5-HT

or Autocrine signaling

Question 4

What is P2Y?

Answer 4

receptor for ATP

on SUB cells or Sour/Salty cells

Question 5

What is P2X?

Answer 5

ATP receptor on SUB cells

(can do autocrine signaling)

Question 6

How is salt allowed into taste receptors?

Answer 6

Na goes in via ENaC –> diffuses down gradient into cell –> depolarizes membrane –> increased Ca –> 5HT released

Question 7

What molecule do sour foods use to stimulate taste receptors and what is its effect?

Answer 7

H+ from the acid –> inhibits potassium channels from flooding more + charges –> depolarization –> increased Ca –> 5-HT released

Question 8

What type of receptor binds sweet, umami, and bitter flavors?

Answer 8

GPCR

all are Gq

Question 9

What is the general mechanism of SUB taste cell signaling?

Answer 9

SUB molecule binds Gq GPCR –> PLC- IP3 –> increased intracellular Ca –> TRPM5 activation –> Na in –> depolarization –> release of ATP through PanxI channels = NT release

Question 10

What is the specific receptor for umami flavors?

Answer 10

mGluR4 = GPCR for glutamate

Question 11

Where are secondary sensory neuron cell bodies for the ascending taste pathway?

Answer 11

nucleus tractus solitarius

Question 12

How does the brain integrate visual, somatosensory, olfaction, and gustatory stimuli?

Answer 12

VPM –> gustatory cortex –> orbitofrontal cortex

Question 13

How does the brain do emotion and memory associated with eating/

Answer 13

Gustatory cortex –> amygdala

Question 14

How does the brain integrate homeostatic mechanisms of eating (hunger)?

Answer 14

Hypothalamus –> nucleus tractus solitarius

Question 15

Where do medularry reflex arcs occur (salivating, swallowing, etc)?

Answer 15

nucleus tractus solitarius

Question 16

What type of cells are olfactory cells?

What are their receptor proteins?

Answer 16

bipolar neurons

GPCRs = Gs

Question 17

What happens when an odorant binds its receptor?

Answer 17

binds Golf –> increased cAMP –> opes CNGC –> cation influx –> depolarization

Question 18

How does odorant desensitization occur?

Answer 18

odorant persists –> sensitivity of CNGC to cAMP decreases –> reduces cation influx

or inactivated by receptor phophorylation

Question 19

What is the relationship btw the number of odor receptors and a glomerulus?

Answer 19

one olfactory neuron expresses the same odorant receptor on all of its cilia

neurons with similar receptors all put their axons into the same glomerulus

Question 20

How do we detect a ton of different odors w/ only ~350 odorant receptors?

Answer 20

one odorant can bind more than one type of OR

Patterns of OR binding –> different smells

Question 21

What NT do granular cells and periglomerular cells release?

Answer 21

GABA –> increases specificity of signal

Question 22

What type of NT do ORNs release?

Answer 22

glutamate

Question 23

What is the major difference btw taste receptors and olfactory receptors?

Answer 23

taste = modified epithelial cells

olfactory receptors = neurons

Question 24

What part of the brain is essential for perception of flavor?

Answer 24

gustatory and olfactory cortices =

medial orbitofrontal cortex

Question 25

What path integrates taste, sight and smell, and allows for appreciation of flavor (but not identification)?

Answer 25

piriform cortex –> thalamus –> medial orbitofrontal cortex

Question 26

What does the anterior olfactory nucleus do in smell?

Answer 26

poorly understood

goes to bilateral cortices and olfactory bulbs

Question 27

Where do all parts of the olfactory cortex go?

Answer 27

DILO

DM thalamic nucleus

Insular and orbital cortex

lateral hypothalamus

olfactory bulb

Question 28

What is the extra place tha the lateral entorhinal cortex go and what is encoded here?

Answer 28

hippocampus

memory formatio and recall related to smell

Question 29

What does the piriform cortex help encode?

Answer 29

control of appetite

Question 30

What does the anterior cortical amygdaloid nucleus do?

Answer 30

emotional learning, smell fear conditioning

Question 31

What does the periamygdaloid cortex do?

Answer 31

integrates emotional aspects elicited by odor