Lecture 24 Flashcards
1
Q
how is cone photopigment distributed
A
not equally
2
Q
how many short wave lengths sensitive comes are there
A
5-10%
3
Q
ration of L:M cones
A
2:1
4
Q
dark current
A
- cGMP binds to Na+ and Ca+ permeable channel keeping them open
- flow of cations into the outer segment in the dark
- K+ leaves the cell through “leaky” channels in the inner segment
- The Na+/K+ pump maintains the concentrations of Na+ and K+ inside and outside the cell
5
Q
in the dark the membrane potential of photoreceptors is
A
~ -40mV
6
Q
Phototransduction
A
- absorption of light by chromophore (photo-activation or bleaching)
- rhodopsin changes conformation therefore is activated
- active rhodopsin activates a G-protein
- G-protein activates PDE enzyme
- PDE breaks down cGMP to GMP
- cGMP gated channels close
7
Q
What happens to the membrane potential when cGMP-gated ion channels close?
A
oPhotoreceptors become more hyper polarized
8
Q
what forms a vertical pathway in the retina
A
Photoreceptors, bipolar cells, and ganglion cells
9
Q
bipolar cells synapse with ____-
A
neither cones or rods
10
Q
bipolar cells pass info onto
A
RGCs
11
Q
RGCs are
A
- The only neurons whose axons leave the eye
- The only retinal neurons that generate action potentials
- The site at which parallel visual streams emerge
12
Q
Foveal vision allows us to see fine details because
A
- Retinal neurons (except cones) are shifted to one side to allow light unimpeded access to cones
- Cones are tightly packed into foveal regions
- Cones and bipolar cells are connected to each other in a 1:1 ratio (high spatial mapping)
- Fovea has the highest visual acuity, light has a more direct pathway to the back of the eye
13
Q
as you increase eccentricity you _______ convergence
A
increase
14
Q
periphery has higher _______
A
convergence?
15
Q
near fovea has ______ resolution
A
increased
