Vision 1 - Stuff I Don’t Really Know

Question 1

What are visual pigment molecules formed by?

Answer 1

Combining chromophore and an opsin

Question 2

What is compared to a G-protein coupled receptor and what is compared to a ligand?

Answer 2

GPCR: rhodopsin
Ligand: 11-cis retinal

Question 3

What is an opsin?

Answer 3

Large membrane bound protein that regulates biochemical processes within the cell

Question 4

Explain the dark reaction

Answer 4

1. Concentration of cGMP is high
2. Inward Na+ current through cGMP-gated channels which depolarized the cell. This is the dark current which is usually ~-50pA keeping the cell at ~-40mV
3. Depolarization causes transmitter release (glutamate) at terminal region

Question 5

Explain light reaction

Answer 5

1. Light activates rhodopsin
2. Trbsducn, the G-protein is active
3. Phosphodiesterase (PDE) the effector enzyme is activated
4. PDE activity reduces the cGMP level
5. cGMP-gated Na+ channels close —> no Na+ current (dark current)

Question 6

What the two modes of action of Glutamate

Answer 6

Cone terminal: glutamate binds ionotropic receptor (AMPA) which opens cation channels —> leads to depolarization of Off bipolar

Rod terminal: glutamate binds metabotropic (mGluR) which closes cation channels —> hyperpolarization of On bipolar

Question 7

What are the two ways in which one can visualize the receptive fields

Answer 7

1. The set of photoreceptors to which the cell is connected

2. The part of the visual field in which various visual stimuli can affect the discharge rate of the cell

Question 8

What are the three Primate Visual Systems

Answer 8

1. Luminance signal: (black and white) from red and green cones
2. Red-green color signal: compare activity of red and green cones
3. Blue-yellow color signal: compares activity of luminance signal and blue output