Physiology of Vision

Question 1

Direct pathway for signal transmission in the retina

Answer 1

PBG
Photoreceptors –>
Bipolar cells –>
Ganglion cells

Question 2

What is the dark current?

Answer 2

In the dark, a cGMP gated Na+ channel is open

When there is light, this channel closes and the photoreceptor becomes more negative (hyperpolarised)

Question 3

Glutamate levels in the light/dark?

Answer 3

More glutamate in the dark, less glutamate in the light

LESS IN THE LIGHT

Question 4

This is the part of the retina that needs to be stimulated to elicit action potentials from a ganglion cell

Answer 4

“Receptive field”

Question 5

What is visual acuity?

Answer 5

The ability to distinguish between 2 nearby points

-determined largely by photoreceptor spacing and refractive power

Question 6

Seeing in dim light

Answer 6

Rods

Question 7

Seeing in normal daylight

Answer 7

Cones

Question 8

Why can you see different colours?

Answer 8

Different cones for different wavelengths

Question 9

Glutamate receptor in the OFF pathway

Answer 9

Ionotropic glutamate receptor

Question 10

Glutamate receptor in the ON pathway?

Answer 10

Metabotropic glutamate receptor

Question 11

High convergence
High sensitivity
Low ACUITY

Answer 11

Rods

Question 12

Low convergence
Low sensitivty
HIGH ACUITY

Answer 12

Cones

Question 13

These photoreceptors let us see colour

Answer 13

Cones

Question 14

These are found in the central retina (fovea)

Answer 14

Cones

Question 15

Chromatic
Central retina (fovea)
Low convergence
Low light sensitivity
High visual acuity

Answer 15

Cones

Question 16

Achromatic
Peripheral retina
High convergence
High light sensitivity
Low visual acuity

Answer 16

Rods

Question 17

The only cells that can produce action potentials

Answer 17

Ganglion cells (and sometimes amacrine)

Question 18

What do ON bipolar cells detect?

Answer 18

Increased in luminance

way to remember –> if light is ON there is LUMINENCE !!

Question 19

What do OFF bipolar cells detect?

Answer 19

Decrease in luminence

Question 20

Nerve fibres from which half of the retina cross over at the optic chiasm?

Answer 20

Nerve fibres from the NASAL half of the retina cross over at the optic chiasm