BS - Retinal Receptive Fields - Week 5

Question 1

Why is simple detection not enough for the human visual system, and what does this result in evolutionarily?

Answer 1

The system cant tell if a spot is off-centre from a receptor field.
Centre-surround receptive fields are used to more easily detect whether stimuli are on- or off-centre.

Question 2

What pathway generates receptive fields, and name two cells involved.

Answer 2

The lateral pathway, mediated by horizontal and amacrine cells.

Question 3

What do horizontal cells mediate specifically, what two cells do they contact, how many types are there in primates, and what neurotransmitter do they use?

Answer 3

Mediates spatial interactions between receptors.
It contacts receptors and bipolar cells.
It uses inhibitory GABA, and there are two types in primates (H1, H2).

Question 4

What do amacrine cells mediate specifically, what two cells do they contact, how many types are there in primates, and what neurotransmitters do they use?

Answer 4

Regulatory and spatial interactions between bipolar and ganglion cells, mostly inhibitory.
Uses GABA and glycine
Over 30 types in primates

Question 5

Consider the two types of horizontal cells. What type of cell does each one contact?

Answer 5

H1 - cones and rods
H2 - cones
H3 - red/green cones

Question 6

Describe how a horizontal cell generates a centre-surround receptive field.

Answer 6

It contacts photoreceptors, which have a centre excitation.
Horizontal cells themselves have a larger surround inhibition.
The common bipolar cell between them therefore has the overlapping centre-surround receptive field.

Question 7

What input modulates the centre of centre-surround receptive fields?

Answer 7

Inhibitory input.

Question 8

Describe what happens to the following when light stimulates centre and surround:
Glutamate level
GABA levels
Effect on Cl- channels
ON-BC
OFF-BC

Answer 8

Less glutamate
Less GABA
Less Cl- efflux from ON/OFF BCs
-Less relative depolarisation of ON-BC to light
-Less relative hyperpolarisation of OFF-BC

Question 9

Describe what happens to the following when light stimulates centre only.

Answer 9

Less glutamate from the centre cone.
ON-BC depolarises
OFF-BC hyperpolarises
GABA release keeps Cl- channels open
ON-BC - more relative depolarisation
OFF-BC - more relative hyperpolarisation