Visual 1

Question 1

what are the business end of the rods

what are they made of

Answer 1

disks = bags of ECF pinched off

Question 2

what is ultimate consequence of phototransduction

Answer 2

decr in cGMP

Question 3

phototransduction converts what to what

Answer 3

converts light to change in membrane potential by photoreceptors

Question 4

pathway of phototransduction

Answer 4

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)

Question 5

structure of rhodopsin

where is transducing mostly found

where is PDE mostly found

Answer 5

7 TM protein

found in high concentration in disk surrounding rhodopsin

found in cytoplasmic space of disc membrane

Question 6

what happens at basal end of photoreceptor with light and without

what is membrane potential changes in night vs light

Answer 6

with light = K+ leaving photoreceptor vs Na+ normally streaming in

in dark, photoreceptor at -40 mV
with light, -70 mV = reversal potential for K+

Question 7

how do photoreceptor respond to various intensity of light

Answer 7

more intense = more hyperpol = less excitatory NT

Question 8

compare # of photoreceptor to ganglion cell

Answer 8

multiple photoreceptor and bipolar cell per each ganglion cell

Question 9

distinguish btwn on vs off center ganglion cell

Answer 9

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

Question 10

exam hint a stimulus that was stim the inhibitory ….

circuit was released and rebound depol for firing AP

Answer 10

a

Question 11

what happens to response when light is turned on?

what happens when light turned off

Answer 11

more or less AP

rebound depol

Question 12

compare receptive field size in fovea vs retina

Answer 12

larger in periphery

Question 13

key determinant in receptive field type of ganglion cells is ___

Answer 13

type of receptor on bipolar cells

Question 14

on-center bipolar cell pathway

Answer 14

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

Question 15

role of horizontal cells?

Answer 15

when excited by glutamate, release GABA to inhib neighboring photoreceptors in receptive field

reinforce vertical pathway and excite retinal ganglion cell

Question 16

effect of light on center for ON-CENTER GANGLION (INHIB GLUT RECEPTOR)

Answer 16

1) light on center
2) hyperpol photoreceptor
3) decr glut release
4) inhib bipolar cell, incr excitation of ganglion cell

Question 17

effect of light on center for OFF-CENTER GANGLION (EXCIT GLUT RECEPTOR)

Answer 17

1) light on center
2) hyperpol photoreceptor
3) decr glut release
4) decr excitation of bipolar cell, incr inhib of ganglion cell

Question 18

what happens if no light in periphery of ON CENTER GANGLION CELL RECEPTIVE FIELD

Answer 18

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

Question 19

2 excitatory synapses in pathway

1 inhib

1 excit or inhib

Answer 19

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

Question 20

cones of diff color preferences converge where?

creates?

Answer 20

cones of diff color preferences converge in retina

–> creates ganglion cells with receptive fields favoring certain color

Question 21

where is color discrim best?

what are color opponent ganglion cells

Answer 21

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

Question 22

primary visual pathway for process form and color

Answer 22

genticulostriate from LGN of thal to V1

Question 23

difference btwn parvocellular ganglion cell and magnocellular pathway

Answer 23

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

Question 24

color processing is handled where?

blob cells receive input from …

Answer 24

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

Question 25

color info from blob cells travel to where?

stripe region of V2 receive input from …

V4 is made of what?

Answer 25

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

Question 26

lesions in V4 =?

Answer 26

impaired recog of color

Question 27

cells in V1 are organized how?

Answer 27

organized in hypercolumns

adjacent columns = adjacent retinal locations

Question 28

describe pinwheel

Answer 28

orientations of lines in visual field lie in pinwheels that radiate from central blobs
all cells in vertical column sensitive to same orientation