Physiology of Vision

Question 1

List some important characteristics of rods

Answer 1

-high sensitivity, specialized for night vision
-high amplification because of higher density of rods to cones and more connections to bipolar cells
-achromatic: one pigment
-free-floating discs

Question 2

List some important characteristics of cones

Answer 2

-low sensitivity, specialized for day vision
-less amplification
-chromatic: three types of pigment

Question 3

What is the phototransduction process?

Answer 3

1. light activated rhodopsin by converting tis 11-cis retinal to the all trans state
2. this leads to formation of metarhodopsin II which triggers the next steps in the process
3. the semi-stable intermediate form of rhodopsin then converts back to its original state

Question 4

What is the dark current?

Answer 4

The resting photoreceptor potential that is slightly depolarized because of Na+ entry, occurs when its dark

Question 5

how is receptor potential generated?

Answer 5

after light activates rhodopsin, the g-protein transducin is stimulated which in turn activates cGMP phosphodiesterase which decreases cGMP and closes the Na+ currents of the “dark current”

Question 6

Describe the effects of on-center/off-surround

Answer 6

light excited (depolarizes) the center bipolar cell, increasing APs while inhibiting (hyperpolarizing) the surrounding bipolar cells, decreasing APs

Question 7

Describe the effects of off-center/on-surround

Answer 7

Light inhibits (hyperpolarizes) the center bipolar cell, decreasing APs while light excites (depolarizes) the surrounding bipolar cells, increasing APs

Question 8

Why are there different bipolar cell responses?

Answer 8

Opposite effects of the glutamate neurotransmitter on the postsynaptic membrane

Question 9

What is the lateral geniculate nucleus?

Answer 9

It receives visual information from the retina and sends it to the primary visual cortex area of the cerebral cortex for processing

Question 10

What are the receptive fields of the visual cortex?

Answer 10

Simple, complex and movement-sensitive complex cells

Question 11

What are simple cells and what do they do?

Answer 11

They respond best to bars of light that have the correct position and orientation and represent the converging input from the round lateral geniculate receptive fields

Question 12

what are complex cells and what do they do?

Answer 12

They are larger receptive fields that may depend on an edge of the field being illuminated and represent converging input from a group of simple cells having the same axis of orientation

Question 13

perception of color depends on what?

Answer 13

simulation of at least two sets of photoreceptors

Question 14

what are the color vision receptive fields?

Answer 14

green vs. red and blue vs. yellow (red+green)