Lecture 24 Flashcards
how is cone photopigment distributed
not equally
how many short wave lengths sensitive comes are there
5-10%
ration of L:M cones
2:1
dark current
- 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
in the dark the membrane potential of photoreceptors is
~ -40mV
Phototransduction
- 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
What happens to the membrane potential when cGMP-gated ion channels close?
oPhotoreceptors become more hyper polarized
what forms a vertical pathway in the retina
Photoreceptors, bipolar cells, and ganglion cells
bipolar cells synapse with ____-
neither cones or rods
bipolar cells pass info onto
RGCs
RGCs are
- The only neurons whose axons leave the eye
- The only retinal neurons that generate action potentials
- The site at which parallel visual streams emerge
Foveal vision allows us to see fine details because
- 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
as you increase eccentricity you _______ convergence
increase
periphery has higher _______
convergence?
near fovea has ______ resolution
increased
P-ganglion cell recieves input from
midget bipolar cells
P-ganglion cell size is
small
P-ganglion cell is _____% of all RGCs
~70
P-ganglion cell are high in density in the ___
fovea
M-ganglion cell receives input from
diffuse bipolar cells
M-ganglion cell size is
large
M-ganglion cell has ______ dendritic field
large
P-ganglion cell has ______ dendritic field
small
M-ganglion cell is ___% of all RGCs
~10
what is a third type of ganglion cell in RGCs
koniocellular
Retina does not just detect light it
detects differences in light in adjacent parts of the retina
Receptive field
area of the retina (or visual field) that influences the neuron, either by inhibition or excitation
2 concentric zones
Excitatory+inhibitory = centre- surround receptive field
