Visual 1 Flashcards
what are the business end of the rods
what are they made of
disks = bags of ECF pinched off
what is ultimate consequence of phototransduction
decr in cGMP
phototransduction converts what to what
converts light to change in membrane potential by photoreceptors
pathway of phototransduction
1) photon abs by retinal (pigment in rhodopsin
2) changes conformation of cis to trans retinal
3) conformational change in rhodopsin –> metarhodopsin
4) metarhodopsin activates GTP binding protein (transductin)
5) transducin activate cGMP PDE
6) cGMP PDE active as long as trasducin bound
7) decr cGMP , closes cGMP gated NSC in surface membrane
8) photoreceptor hyperpol, decr NT release via electronic transmission (no AP)
structure of rhodopsin
where is transducing mostly found
where is PDE mostly found
7 TM protein
found in high concentration in disk surrounding rhodopsin
found in cytoplasmic space of disc membrane
what happens at basal end of photoreceptor with light and without
what is membrane potential changes in night vs light
with light = K+ leaving photoreceptor vs Na+ normally streaming in
in dark, photoreceptor at -40 mV
with light, -70 mV = reversal potential for K+
how do photoreceptor respond to various intensity of light
more intense = more hyperpol = less excitatory NT
compare # of photoreceptor to ganglion cell
multiple photoreceptor and bipolar cell per each ganglion cell
distinguish btwn on vs off center ganglion cell
on = excited by light in centers causing rGC to incr activity
and inhib by light in periphery
off= excited by light in periph and inhib by light in center
exam hint a stimulus that was stim the inhibitory ….
circuit was released and rebound depol for firing AP
a
what happens to response when light is turned on?
what happens when light turned off
more or less AP
rebound depol
compare receptive field size in fovea vs retina
larger in periphery
key determinant in receptive field type of ganglion cells is ___
type of receptor on bipolar cells
on-center bipolar cell pathway
1) light hyperpol photoreceptor, decr glutamate release
2) removes inhibition of ON-bipolar cell so it releases glutamate (has mGluR6 receptor inhib by glutamate)
3) excite retinal ganglion cell and fire AP at freq = intensity
role of horizontal cells?
when excited by glutamate, release GABA to inhib neighboring photoreceptors in receptive field
reinforce vertical pathway and excite retinal ganglion cell
effect of light on center for ON-CENTER GANGLION (INHIB GLUT RECEPTOR)
1) light on center
2) hyperpol photoreceptor
3) decr glut release
4) inhib bipolar cell, incr excitation of ganglion cell
effect of light on center for OFF-CENTER GANGLION (EXCIT GLUT RECEPTOR)
1) light on center
2) hyperpol photoreceptor
3) decr glut release
4) decr excitation of bipolar cell, incr inhib of ganglion cell
what happens if no light in periphery of ON CENTER GANGLION CELL RECEPTIVE FIELD
1) photoreceptor in periph remain depol
2) glut release
3) activate excitatory receptor on horiz cells
4) horiz cell release GABA on to photoreceptors in field center
5) inhib photoreceptors
6) further decr glut release on bipolar cell and release inhib of bipolar
7) bipolar release glut on to ganglion to excite and incr firing rate
2 excitatory synapses in pathway
1 inhib
1 excit or inhib
1) surround photoreceptor to horiz cells
2) bipolar cell to ganglion cell
1) horiz cell to photoreceptor synapse
1) field center photoreceptor to bipolar cell
cones of diff color preferences converge where?
creates?
cones of diff color preferences converge in retina
–> creates ganglion cells with receptive fields favoring certain color
where is color discrim best?
what are color opponent ganglion cells
in fova because all cones so most of bipolar cells connected to one cone in field center and indirectly via horiz cells to cones of diff color preference
–> RED ON-CENTER AND GREEN OFF-SURROUND FIELD passed to ganglion cell = color opponent cells
also blue-yellow opponent cells spanning entire spectrum
primary visual pathway for process form and color
genticulostriate from LGN of thal to V1
difference btwn parvocellular ganglion cell and magnocellular pathway
parvocellular = color sensitive
- project to 4 parvocellular layers of LGN
- slow conducting = perception of color and acuity
magnocellular = no color
- project to 2 magnocellular layers of LGN
- fast conducting = perception of stim change = motion
color processing is handled where?
blob cells receive input from …
in center of hypercolumns = blobs = layer 2?
receive input from many color opponent neurons
receptive field positions overlap entirely so no spatial or light info
color info from blob cells travel to where?
stripe region of V2 receive input from …
V4 is made of what?
travel ventrally from V1 to V2 then V4 to temporal lobe
stripe region of V2 receive input from color blobs in V1
V4 = large receptive field in central retina, respond to narrow wavelength due to lateral inhib at higher level of color processing
lesions in V4 =?
impaired recog of color
cells in V1 are organized how?
organized in hypercolumns
adjacent columns = adjacent retinal locations
describe pinwheel
orientations of lines in visual field lie in pinwheels that radiate from central blobs
all cells in vertical column sensitive to same orientation
