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Neuro exam 3 > Vision > Flashcards

Flashcards in Vision Deck (31):
1

Phototransduction is the

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

2

photon is absorbed by

molecule retinal, a pigment in rhodopsin

3

absorption of photon results in

change in conformation of cis-retinal to trans-retinal

4

the conformational change of cis to trans rhodopsin results in

conformational change in rhodopsin to metarhodopsin

5

metarhodopsin activates

GTP binding protein called transducin

6

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

activate about 500 other transducin molecules

7

Transducin is found

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

8

Each activated transducin molecule remains active for

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

9

Transducin functions to

binds and activates a cGMP phosphodiesterase (PDE)

10

PDE exists

in large numbers attached to the cytoplasmic surfaces of disc membranes

11

cGMP PDE molecule is active:

long as the transducin bound to it remains active

(tens of milliseconds)

12

A decrease in the concentration of cGMP leads to a

closing of non-selective cation channels in the surface membrane

13

The final result of phototransduction is

the cell becomes hyperpolarized

14

Color opponent cells:

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).

15

Cones of different color preferences

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

16

where is color discrimination best

fovea, because all the photoreceptors are cones

17

how is the fovea's color discrimination best?

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.

18

Color information is separated out from spatial information in the

retina.

19

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

geniculostriate

20

geniculostriate pathway

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

21

geniculostriate: ganglion cells

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

22

Color processing is handled in

central regions of the hypercolumns called “blobs”

23

Blob cells:

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

24

Color information from the blob cells travels

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

coursing through regions of V2 and then onto area V4.

25

The stripe regions of V2 receive inputs from:

the color blobs in V1.

26

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

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.

27

Lesions in V4 can result in

impairments in color discrimination.

28

The parvocellular ganglion cells are ____

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

29

The slow-conducting parvocellular pathway mediates _______.

our perception of color and acuity

30

The magnocellular ganglion cells are ___

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

31

the fast-conducting magnocellular pathway is responsible for _____

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