Physiology of vision

Question 1

Describe the pathway of light in the retina in terms of the cellular layers?

Answer 1

Ganglion cell
Bipolar cell
Photoreceptos

Question 2

Describe the direction of signal in the retina in terms of cellular layers

Answer 2

Photoreceptors
Bipolar cells
Ganglion cells

Question 3

In what light conditions will the glutamate release be at its highest?

Answer 3

Dark

Question 4

What does light do to rhodopsin?

Answer 4

Converts 11-cis -retinal to all-trans retinal

Question 5

Will light open or close sodium channels?

Answer 5

Closes them

Question 6

Will light increase or decrease cGMP levels within the retina?

Answer 6

Decrease

Question 7

Do rods show high or low convergence?

Answer 7

High (and therefore cones show low)

Question 8

What is the impact of a higher convergence in the rod system?

Answer 8

Increased sensitivity whilst decreasing acuity

Question 9

Describe the 3 different cones and the light they process

Answer 9

Short wave = blue
Medium wave = green
Long wave = red

Question 10

Describe the OFF pathway in the retina

Answer 10

Dark = more glutamate
Ionotropic receptors on bipolar cells
Membrane is more positive
Ganglion cell is more positive; action potential

Question 11

Describe the ON pathway in the retina

Answer 11

Light; less glutamate
Metabotropic receptors on bipolar cells resulting in decreased calcium and increased potassium
Membrane more positive
Ganglion cell more positive; action potential

Question 12

What is the function of lateral inhibition?

Answer 12

Exaggerates the difference in stimulus intensity detected by adjacent neurones
Aids with localization

Question 13

What neurotransmitter will horizontal cells release?

Answer 13

GABA

Question 14

What is the center surround organisation in the retina?

Answer 14

Ganglion cells have an either an ON centre and OFF surround or OFF centre and ON surround

Question 15

What is the purpose of the center surround organization?

Answer 15

Emphasize areas of contrast; i.e. it sharpens the boundary between objects of different luminance

Question 16

What are the different types of retinal ganglion cells?

Answer 16

M - movement

P - form and colour

Question 17

Which fibres from the eyes will decussate?

Answer 17

Nasal fibres at the optic chiasm

Question 18

Which layer of the primary visual cortex is vision processed?

Answer 18

Layer 4C

Question 19

What is the purpose of the cortical receptive fields?

Answer 19

Orientation selectivity

Responds to light and dark