Chemical Senses: Smell and Taste

Question 1

Do we often associate individual molecules with objects?

Answer 1

Nope, it’s often a complex mix of molecules

Question 2

Review: How long are the olfactory nerves?

Answer 2

Really short… just running in the cribriform plate

Question 3

What area of the brain is responsible for smell detection?

Answer 3

The pyriform cortex

Question 4

What area of the brain is responsible for connecting smell with emotion?

Answer 4

The amygdala

Question 5

What is the accessory olfactory system used for?

Answer 5

Individuals of the same species signaling to eachother (sex, fear, etc.)

Question 6

3 types of cells in the olfactory epithelium?

Answer 6

Olfactory Sensory Neurons (OSNs) aka Receptor Cells, Supporting cells, Basal cells

Question 7

What do the basal cells do?

Answer 7

Stem-cell like: give rise to olfactory neurons and support cells

Question 8

What kind of receptor do odorants hit?

Answer 8

GPCRs - with G(olf)

Question 9

2nd messenger used in olfactory receptors? Downstream effects?

Answer 9

cAMP, depolarization with Na+ and Ca++ influx

Question 10

Do we have a lot of genes for olfactory receptors?

Answer 10

Yes, about 400 functional genes (though most animals have more). Largest gene superfamily in genome.

Question 11

How many types of odorant receptors are on one neuron?

Answer 11

One.

Question 12

Is there a 1:1 relationship between odorant and receptor?

Answer 12

No. That wouldn’t make sense, as there are more about 400 things in the world to smell. One receptor can bind many molecules, one molecule may bind many receptors.

Question 13

How are odor quality and intensity encoded?

Answer 13

Combinations of multiple receptors/neurons.

Question 14

3 types of cells in the olfactory bulb?

Answer 14

Mitral/tufted cells, periglomerular cells, granule cells

Question 15

What do the mitral/tufted cells do?

Answer 15

Receive inputs from OSNs, send axons to higher cortical regions (they do the real business here)

Question 16

What do the periglomerular cells do?

Answer 16

Modulate inputs to mitral/tufted cells from OSNs

Question 17

What do the granule cells ddo?

Answer 17

Modulate outputs from mitral/tufted cells to cortical regions

Question 18

What are the glomeruli in the olfactory bulb?

Answer 18

Clusters of dendrites of mitral/tufted cells all receiving input from OSNs with the same receptor.

Question 19

How would you describe the area that signaling from one type of olfactory receptor activates in the piriform cortex?

Answer 19

A disperse field of neurons for “ensemble coding”

Question 20

3 ways to mess up olfaction?

Answer 20

conduction, sensineural (ciliopathy, shear injury after head trauma), central olfactory neural impairment

Question 21

What’s one test to evaluate olfaction clinically?

Answer 21

UPSIT - UPenn Smell Identification Test

Question 22

What happens to smell when you get old? Why?

Answer 22

It gets worse. Vascular or mass lesions, and neurodegenerative disorders.

Question 23

The 5 tastes? Which ones use ion channels? What do the rest use?

Answer 23

Salty (Na+) and sour use ion channels. Bitter, sweet, and Umami use GPCRs.

Question 24

What area of the thalamus does taste hit?

Answer 24

VPM nucleus

Question 25

Where’s the primary gustatory cortex?

Answer 25

The insula - deep in the Slyvian fissure (aka lateral sulcus). Recall destroying your brains’ cortices to look at it.

Question 26

Where do taste afferents first synapse?

Answer 26

In the nucleus of the solitary tract.

Question 27

What specific channel is used for Na+ tasting?

Answer 27

ENaC (epithelial Na+ channel)

Question 28

What specific channel is used for H+ tasting?

Answer 28

TRP (transient receptor potential) channel

Question 29

What do protons do to the ion channels?

Answer 29

open them, allowing Na+ in

Question 30

What is the second messenger system in bitter, sweet, Umami GPCRs?

Answer 30

gustducin -> IP3 -> Ca++ influx -> depolarization

Question 31

What is “labeled-line coding”?

Answer 31

Brain has specialized areas wired to the cells with a specific type of taste receptor. (contrast with diffuse, combinatorial coding of olfaction)

Question 32

Why do medications often cause reduced taste?

Answer 32

Dry mouth. And you need saliva to taste things.

Question 33

When a patient comes in saying they can’t taste, what should you do?

Answer 33

See if they really mean that they can’t smell.