L9 - Chemical Senses 2

Question 1

What is the molecular receptice range in olfaction?

Answer 1

The range of a particular receptor

Question 2

What is the olfactory bulbar structure?

Answer 2

Olfactory nerve layer
Glomerular layer 
External plexiform layer
Mitral cell layer
Granule cell layer

Question 3

In the external plexiform layer what is the excitatory path?

Answer 3

Mitral cell to granule cell

Question 4

In the external plexiform layer what is the inhibitory path?

Answer 4

Granule cell to mitral cell

Question 5

What are the suggested functions of granule cells?

Answer 5

Gain control
Cpntrast
Bulbar oscillations
Odour recognition/memory

Question 6

Outline recurrent and lateral inhibition of mitral cells

Answer 6

Odour excites glomerulus with mitral cell A –> granule cell connected to A gets excited –> recurrent feedback inhibition of mitral cell A and lateral inhibition of mitral cell B

Question 7

What are the two methods of contrast enhancement of glomerular maps?

Answer 7

Lateral inhibition in the olfactory bulb

Non-topographical contrast enhancement

Question 8

What are the frequencies of oscillatory activities in the olfactory bulb?

Answer 8

Theta 5-10Hz. Synchronised to breathing rhythm/sniffing
Beta 20-40Hz. M/TC granule cell interaction driven by top -Down input
Gamma. 40-100Hz. M/TC granule cell interaction

Question 9

Why aren’t humans able to smell aswell as rodents?

Answer 9

Wehave change blindness due to our slower and irregular breathing pattern

Question 10

Is the granule cell spine a mini neuron?

Answer 10

They do fire APs in vivo however transmitter release can occur without an AP. The spine thus acts like a micro circuit or mini neuron which enhances the computational power of the bulbar network by providing each granule cell withseverl hundreds of independent micro

Question 11

What is 2 photon flourescence microscopy?

Answer 11

Uses both IR and UV

Much deeper with less photo damage

Question 12

What is a line scan?

Answer 12

Scans an x-y line of interest with high temporal resolution. The neuron is stimulated. The intensity is projecred onto the temporal axis analysis is done by relative flourescence change.

Question 13

Outline to go-no go task by abraham et al

Answer 13

Odour S+ - gave a reward if the mouses head stayed
Odour S- head retraction
Used both simple discrimination (odour a vs odour b) and difficult discrimination (0.6A 0.4B vs 0.4A 0.6B)
Found that the mice discriminated each equally well however it took longer for the more complex stimulus.

Question 14

Outline the granule cell specific modification of ionotropic glutamate receptors, genetic mutation findings.

Answer 14

GluA2 deletion –> AMPA Ca2+ permeable –> a larger calcium and gaba gradienf leading to a gain of function
GluA1 deletion makes NMDA receptors calcium impermeable leading to a decrease in calcium and therfore a decrease in GABA leading to a loss of function.
Therefore granule cell mediated inhibition contributes to fine odour discrimination.

Question 15

What are the neuromodulatry centrifugal inputs in olfaction?

Answer 15

HDB
locus coerulus
Raphé nucleus

Question 16

What is the function of the piriform cortex?

Answer 16

Synthesizing olfactory objects and performing background subtraction
In humans it is active during learning and memory of new odours

Question 17

In drosophila how can hedonic valence of odorants me measured?

Answer 17

Using the trap assay

So attraction index = flies in odour trap - flies in control trap/ all flies

Question 18

What is agenisia?

Answer 18

Trauma causing damage to the olfactory nerve

Question 19

What are the rules of olfactory coding?

Answer 19

Rule 1: 1 ORN expresses 1 OR
Rule 2: 1 ORN projects to 1-2 glomeruli
Rule 3: An OR recognises molecular structural epitopes
Rule 4: An epitope can bind several odourants