Olfaction

Question 1

What detects airborne odorants?

Answer 1

The olfactory epithelium in the nasal cavity

Question 2

How do some species enlarge the olfactory epithelium

Answer 2

Turbinates

They also improve airflow contact

Question 3

What happens to odorants that reach the olfactory epithelium

Answer 3

Dissolve in the mucus film (possibly in association with an odorant binding protein) and then interact with receptors on the olfactory cilia

Question 4

How often are olfactory receptors renewed?

Answer 4

Every 60 days by basal cell division

Question 5

Whete does olfactory transduction take place

How does it work (give the cascade)

Answer 5

In the olfactory cilia

• The odorant interacts with the receptor molecule (a GPCR) which activates Golf (a G protein)
• Golf stimulates AC to produce cAMP
• cAMP opens cyclic nucleotide gated cation channels in the ciliary membrane, allowing Ca2+ and Na+ to enter and depolarise the cell, firing APs
• Ca2+ open Ca2+ gated Cl- channels and Cl- ions exit the cell, augmenting the depolarisation

Question 6

does the receptor current change with [odorant]?

Answer 6

Current increases as [odorant] increases

Question 7

Which ion is principally involved in olfactory adaptation

What is the mechanism

Answer 7

Ca2+

Calcium acts via calmodulin to reduce the sensitivity of the cation channels to cAMP thus contributing to olfactory adaptation

Question 8

How is Ca2+ extruded from olfactory receptor cells

Answer 8

Na+/Ca2+ exchanger

Ca2+ ATPase May contribute in some species

Question 9

True or false

Each olfactory receptors cell expresses only one receptor molecule and therefore only responds to one odorant

Answer 9

False

Each olfactory receptors cell expresses only a single receptor molecule type, but responds to a range of odorants

Question 10

Where do olfactory receptor axons pass

Answer 10

Through the cribriform plate to the olfactory bulb

Question 11

What do olfactory receptor axons excite at the olfactory bulb

Answer 11

Mortal cells and tufted cells in the olfactory glomeruli

Afferents from olfactory receptors cells, expressing a particular receptor molecule, selectively converge on just to glomeruli in each bulb

Question 12

Which are bigger in size:

Mortal cells or tufted cells in the olfactory glomeruli

Answer 12

Mitral > tufted cells

Question 13

Does lateral inhibition exist in the olfactory bulb

Answer 13

Yes- Peri glomerular cells and granule cells make reciprocal dendro-dendritic synapses with mitral cells

Question 14

What is the point of lateral inhibition in the olfactory bulb

Answer 14

Sharpens mitral cell odour tuning

Question 15

What patterns do different odours make in the olfactory bulb

Answer 15

Different odorant invoke distinct but overlapping activity patterns in the bulb

Question 16

How do mitral cell axons leave the bulb

Answer 16

In the lateral olfactory tract

Question 17

What does the anterior olfactory nucleus mediate

Answer 17

Mediates Inhibition between 2 bulbs via the anterior commissure

Question 18

Where does the lateral olfactory tract synapse

Answer 18

On neurons in 5 regions of olfactory cortex:

Anterior olfactory nucleus
Olfactory tubercle
Pyriform cortex
Amygdala
Entorhinal cortex

Question 19

Where does the olfactory tubercle projects to?

Where does this in turn project to?

Answer 19

The medial dorsal nucleus of the thalamus

The orbitofrontal cortex

Question 20

What does the orbitofrontal cortex do

Answer 20

Mediates the conscious perception of odour

Question 21

What does the pyriform cortex project to

Answer 21

The other olfactory cortical regions

Question 22

Which of the regions that the lateral olfactory tract synapses with form part of the limbic system

What are they involved in

Answer 22

The amygdala and entorhinal cortex

The affective component of odour perception, mediating emotional and autonomic responses

Question 23

How does odour specificity change throughout the olfactory pathway

Answer 23

At higher levels, cells become progressively more odour specific

Eg The majority of cells in the bulb respond to many odorants while those in the orbitofrontal cortex respond to just 1 or 2

Question 24

What mediates response to pheromones

Where does it project to

Answer 24

The vomeronasal organ

Projects via the accessory olfactory bulb to the amygdala

Question 25

What are pheromones involved in

What else can be involved in social recognition signals

Answer 25

Sexual and social behaviour

MHC peptides

Question 26

What are TAARs ?

Answer 26

Trace Amine Associated Receptors

In humans, they are in the main olfactory epithelium and detect volatile amines in sweat to shift mood and perhaps increased fertility