Vision

Question 1

Phototransduction is the

Answer 1

process by which light is converted to a change in membrane potential by photoreceptors.

Question 2

photon is absorbed by

Answer 2

molecule retinal, a pigment in rhodopsin

Question 3

absorption of photon results in

Answer 3

change in conformation of cis-retinal to trans-retinal

Question 4

the conformational change of cis to trans rhodopsin results in

Answer 4

conformational change in rhodopsin to metarhodopsin

Question 5

metarhodopsin activates

Answer 5

GTP binding protein called transducin

Question 6

Before being inactivated by phosphorylation (after about 200 milliseconds), one transducin molecule can _____

Answer 6

activate about 500 other transducin molecules

Question 7

Transducin is found

Answer 7

in high concentration in the disc membrane surrounding the rhodopsin molecules.

Question 8

Each activated transducin molecule remains active for

Answer 8

tens of milliseconds before its bound GTP is converted back to GDP (transducin has intrinsic GTPase activity)

Question 9

Transducin functions to

Answer 9

binds and activates a cGMP phosphodiesterase (PDE)

Question 10

PDE exists

Answer 10

in large numbers attached to the cytoplasmic surfaces of disc membranes

Question 11

cGMP PDE molecule is active:

Answer 11

long as the transducin bound to it remains active

tens of milliseconds

Question 12

A decrease in the concentration of cGMP leads to a

Answer 12

closing of non-selective cation channels in the surface membrane

Question 13

The final result of phototransduction is

Answer 13

the cell becomes hyperpolarized

Question 14

Color opponent cells:

Answer 14

1. all combinations of red-green on-off opposing fields exist.
2. In addition to red-green opponents, there are blue-yellow opponent cells, thereby spanning the entire spectrum

(the yellow selectivity is created by converging both red and green cones).

Question 15

Cones of different color preferences

Answer 15

converge in the retina to produce ganglion cells with receptive fields that are partial to particular colors.

Question 16

where is color discrimination best

Answer 16

fovea, because all the photoreceptors are cones

Question 17

how is the fovea’s color discrimination best?

Answer 17

1. all the photoreceptors are cones.
2. most of the bipolar cells are connected:

a. directly to one kind of cone in the field center and
b. indirectly (via horizontal cells) to cones with a different color preference in the field surround.
3. This creates a RED ON-center and GREEN OFF-surround receptive field, which is passed along to the ganglion cells.

Question 18

Color information is separated out from spatial information in the

Answer 18

retina.

Question 19

The ____ is the primary visual pathway for the processing of form and color.

Answer 19

geniculostriate

Question 20

geniculostriate pathway

Answer 20

It extends from the retina through the lateral geniculate nucleus (LGN) of the thalamus to the primary visual cortex (V1)

Question 21

geniculostriate: ganglion cells

Answer 21

carry information from the retina to the LGN are of two types, each named for the LGN layer to which they project.

Question 22

Color processing is handled in

Answer 22

central regions of the hypercolumns called “blobs”

Question 23

Blob cells:

Answer 23

1. care ONLY about color
2. receive input from many color-opponent neurons
3. The positions of all these fields overlap entirely, so there is no spatial information in the color-only blob cell’s response.
4. DO NOT CARE ABOUT LIGHT

Question 24

Color information from the blob cells travels

Answer 24

ventrally from V1 (primary visual cortex) to the temporal lobe,

coursing through regions of V2 and then onto area V4.

Question 25

The stripe regions of V2 receive inputs from:

Answer 25

the color blobs in V1.

Question 26

In area V4, anterior and inferior to the primary visual cortex (V1), cells have:

Answer 26

1. relatively large receptive fields in the central areas of the retina
2. respond only to fairly narrow bands of wavelengths over the visible spectrum, some as narrow as 10 mm.

Question 27

Lesions in V4 can result in

Answer 27

impairments in color discrimination.

Question 28

The parvocellular ganglion cells are ____

Answer 28

color-sensitive and project to the four parvocellular layers of the dLGN.

Question 29

The slow-conducting parvocellular pathway mediates _______.

Answer 29

our perception of color and acuity

Question 30

The magnocellular ganglion cells are ___

Answer 30

achromatic and project to the two magnocellular layers of the LGN.

Question 31

the fast-conducting magnocellular pathway is responsible for _____

Answer 31

our perception of stimulus change (including motion) and is largely color-blind.