Physiology of smell - Olfactory System

Question 1

What type of receptors are for taste and smell?

Answer 1

Chemoreceptors

Question 2

What can taste and to a lesser extent smell regulate?

Answer 2

GI secretions

Question 3

Answer 3

Olfactory bulb

Question 4

What is the messenger system used in olfaction?

Answer 4

G-protein second messenger system

Question 5

Answer 5

Question 6

What are the 7 primary qualities of smell?

Answer 6

Peppermint
Musk
Floral
Ethereal
Pungent
Putrid
Comphoraceous

Question 7

What are the second order sensory neurons?

Answer 7

Mitral cells

Question 8

Answer 8

Olfactory bulb

does not pass through the thalamus

Question 9

What do bi-directional projections give rise to?

Answer 9

Smell localisation

Question 10

Where do olfactory pathways from the nose project to?

Answer 10

The cortex

Question 11

When the receptor on cilia is activated, how is the calcium channel opened?

Answer 11

Via a GPCR, activates adenalate cyclase

activates cAMP, which open the calcium channel

Question 12

What is the effect of Ca coming into the nerve?

Answer 12

Cause an AP, and depolarisation

activates chloride channels, Cl- moves out of the cell

Question 13

What is the negative feedback system of Ca2+?

Answer 13

Activates calmldulin,

1. inhibition of cAMP on the Ca2+ channel
2. caMK, inhibit AC

Question 14

What glamerulae are most highly activated?

Answer 14

Red and green

lateral inhibition

Question 15

What are the zones of the olfactory epithelium?

Answer 15

Zone I to IV in the olfactory bulb

Question 16

What does the vomeronasal organ detect?

Answer 16

Pheromones

Question 17

How does the vomeronasal organ connect to the olfactory bulb?

Answer 17

Anterior to the posterior olfactory bulb

Question 18

Does the vomeronasal organ signal to the olfactory in a gradient?

Answer 18

Yes

Question 19

Do humans have a vomeronasal organ?

Answer 19

Likely no

Question 20

What is the competition model?

Answer 20

olfactory neurons are the only neurons in the CNS which can regenerate.

a) the inactive neurons were competed out as they could not bind ligand.

b) neurons not competed out, as the neurons were exposed to a ligand they could both not detect

Question 21

What are olfactory sheathing cells?

Answer 21

Sheathing cells can support regeneration of olfactory bulb neurons

Could regenerate CNS

Question 22

Where do the olfactory receptor neurons project their axons?

Answer 22

through the cribriform plate and into the olfactory bulb

Question 23

What do the olfactory neurons/axons synapse onto in the olfactory bulb?

Answer 23

second order neurons, called mitral cells

Question 24

What is the role of the mitral cells?

Answer 24

send their olfactory neurons down the olfactory tract to the olfactory cortex

Question 25

What happens when the depolarisation threshold is reached in the cilia?

Answer 25

signal transduced to the olfactory cortex

Question 26

How many types of receptor do each olfactory neurons express?

Answer 26

only 1 type of receptor

Question 27

What happens when the axons reach the mitral cells?

Answer 27

they begin to branch = ready for synapse

Question 28

What is a glomerulus?

Answer 28

where the axonal branches and dendrites are synapsing together

Question 29

What do they colours represent in this image?

Answer 29

the neurons which are expressing the same type of receptor

Question 30

Do the grey and pink neurons synapse with the same glomerulus (same mitral cells)?

Answer 30

no, as they express different receptors. the neurons synapse with specific mitral cells for their receptor creating a specific response

there must be axon guidance

Question 31

When can mitral cells inhibit one another?

Answer 31

if they are strongly activated

Question 32

What are the inhibitory cells? (of mitral cells)

Answer 32

granular and perigomerular cells

block out other background smells

Question 33

What do you call the inhibition of background smells to allow us to pick up stronger scents?

Answer 33

sharpening the odour code

Question 34

How is topography achieved in the olfactory system?

Answer 34

The temporal axons have many receptors for the ligand so are inhibited, don’t stretch far into the tectum and are inhibited

nasal axons, from other side of retina (nose), have less receptor for inhibitory ligands.

they can project their axons much further before hey are inhibited.

Question 35

How do we flip the image the right way round again?

Answer 35

The concentration of receptor for inhibitory ligand is on a gradient. the neurons gets flipped and is does the image