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Physiology > Section 3 Visual System > Flashcards

Section 3 Visual System Flashcards

1
Q

Light passes through what before gettign to the rods and cones of the retina?

A

lens, inner layer of ganglion cells and bipolar cells

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2
Q

Where do the photosensors (rods and cones) of the retina lie?

A

The outermost part of the retina

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3
Q

What are the output neurons of the retina?

A

Ganglion cells

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4
Q

Where do ganglion cells lie?

A

innermost in the retina closest to the lens and front of the eye

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5
Q

T or F? The retina contains interneurons.

A

T

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6
Q

Are there more rods or cones?

A

rods, about 20 times more

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7
Q

What color light responds best to short wavelenths?

A

Blue

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8
Q

What color light responds best to medium wavelengths?

A

Green

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9
Q

What color light responds best to long wavelengths?

A

red

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10
Q

Location of the fovea:

A

center of the eye

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11
Q

What is found in the central region of the fovea?

A

Only cones, the overlying retinal layers are displaced

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12
Q

T or F? Only a thin layer of rods are found in the fovea.

A

F. No rods, only cones

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13
Q

Under what conditions does the fovea fxn poorly?

A

Badly lit conditions

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14
Q

At their highest respective density, which has a higher density, rods or cones?

A

cones

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15
Q

To look at an object you move your eye so that the object falls:

A

on the fovea

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16
Q

Under what conditions does the periphery have a higher sensitivity?

A

Dimly-lit condiitons

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17
Q

Does the periphery have a high or poor resolution of small objects?

A

poor

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18
Q

What discs contain rhodopsin molecule in their membranes?

A

Those in the outer segment of rods (about 100 billion molecules per photoreceptor)

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19
Q

What are found in the discs in the outer segment of the rods?

A

Rhodopsin and CNG channels (cation)

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20
Q

When are high levels of cGMP found in the eye?

A

In the dark and keep these channels open.

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21
Q

T or F? A negative charge enters the rod

A

F. positive

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22
Q

What does the entry of a positive charge into the rod lead to?

A

NT release

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23
Q

How does light shut down NT release?

A

Light activates rhodopsin, activates transducin (a G protein), activates cGMP phosphodiesterase (PDE) which hydrolyzes cGMP, this closes the external channels and less current enters.

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24
Q

Does more light mean fewer or more channels are open?

A

Fewer

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25
Q

Under what conditions do the rods release less NT?

A

When light levels increase and the rod hyper polarizes

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26
Q

When fewer channels are open does the cell hypo or hyperpolarize?

A

hyper

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27
Q

Rhodopsin is to rods as ___ is to cones.

A

opsin

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28
Q

This is a hereditary disease of the retina, 10+ mutations in the phototransducation cascade, no cure:

A

Retinitis Pigmentosa

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29
Q

What does Retinitis Pegmentosa lead to?

A

Loss of peripheral vision and blindness

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30
Q

This is in clinical trials to treat Retinitis Pegmentosa:

A

gene therapy to replace a faulty rhodopsin gene

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31
Q

T or F? One photoreceptor synapses onto one postsynapitc interneuron.

A

F. many postsynapitc interneurons

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32
Q

Where do interneurons synapse?

A

Onto one antoher and onto ganglion cells

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33
Q

There are about __ million ganglion cells.

A

One

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34
Q

T or F? The features of the ganglion cells are the same throughout the fovea and periphery.

A

F.

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35
Q

T or F? The features of the ganglion cells are the same throughout the retina.

A

T.

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36
Q

Ganglion cells transmit info about:

A

spatial and temporal contrasts, ie changes in brightness and color or in patterns of light changing

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37
Q

What type of receptor field do most ganglion cells have?

A

Center-surround receptive field

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38
Q

About 50% of center-surround receptive field ganglion cells are:

A

ON-center OFF-surround

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39
Q

To what do ON-center OFF-surround ganglion cells respond best?

A

Small spot of light centered in the receptive field

40
Q

To what do ON-center OFF-surround ganglion cells respond less?

A

To a larger spot of light bc it activated inhibitory inputs to the ganglion cell as well as excitatory inputs

41
Q

To what do OFF-center ON-surround ganglion cells respond best ?

A

a small dark spot on a light background

42
Q

Which type of cell repsonds well to an all-bright or all-dark field?

A

Neither ON-center or OFF-center

43
Q

T or F? Both OFF-center and ON-center cells signal about contrast regardelss of the absolute light level.

A

T.

44
Q

Do ON-center cells respond transiently or with a sustained response?

A

Either

45
Q

Do OFF-center cells respond transiently or with a sustained repsonse?

A

Either

46
Q

Other types of ganglion cells:

A

prefer spec combos and distributions of color in enter and suound (ie red vs. green), don’t have center-surround receptive fields, project to superior colliculus and are involved in eye move control, project to the suprachiasmatic nucleus, a region that controls circadian rhythms

47
Q

Ganglion cells in the center of the fovea are as small as:

A

a fraction of a degree

48
Q

Ganglion cell centers in the periphery can be up to:

A

5 degress in diameter

49
Q

What determines different receptive field sizes?

A

different amounts of convergence from photoreceptor to interneurons (bipolar) to ganglion cells

50
Q

Benefir to lots of convergence in the rod pwy:

A

spatial resolution is degraded (look fuzzy) but sensitivity to low levels of light is improved

51
Q

To which portion of the brain doe the eye send info (where is area 17)?

A

striate cortex

52
Q

About __ % of optic axons project to the lateral geniculate nucleus.

A

90%

53
Q

How do the receptive field properties of the cells in the geniculate compare to those of the retinal ganglion cells?

A

almost the same

54
Q

What is different about the layers of the LGN?

A

diff kinds of ganglion cells project to diff layers (ei color selective vs not will project to diff layers)

55
Q

What does the lateral geniculate nucleus play a role in?

A

selective attention

56
Q

Activation of the LGN comes from:

A

the cortex, brainstem, and thalamic ret for

57
Q

When is transmission into the LGN reduced?

A

sleep and periods of inattentiveness, cells fire spontaneous bursts (why?)

58
Q

Location of the primary visua cortex:

A

(Area 17, Striate cortex, V1) - the pole of the occipital lobe on the medial aspect of the hemisphere

59
Q

What sulcus is adjacent to area 17?

A

calcarine sulcus

60
Q

The largest area of the retinotopic map is devoted to:

A

the fovea

61
Q

Where do axons from lateral geniculate terminate?

A

layer 4

62
Q

To where does info distribute after it leaves area 4?

A

to excitatory or inhibitory, then lower layer for further processing

63
Q

What type of arrangement of connections is there within cortical cells of the cortex?

A

Vertical

64
Q

This is the basic input layer:

A

layer 4

65
Q

Each cell outside of layer 4 responds to the same:

A

orientation

66
Q

How ro respond to different orientation:

A

move to adjacent columns

67
Q

Why is Layer 4 in the striate cortex exceptional?

A

because most cells are center-surround, with circular receptive field

68
Q

What do the vast majority of cells in layers other than 4 respond best to?

A

straight bars or edges, some dark bars or lines, some light bars or lines

69
Q

How is the cortex organized?

A

into columns (30-100 microns in diameter)

70
Q

What is the basic unit in the striate cortex?

A

the orientation column

71
Q

What do all of the cells outside of layer 4 in each column respond best to?

A

the same orientation, some direction selective, some not

72
Q

T or F? All of the cells outside of layer 4 in the striate cortex are direction selective.

A

F. some are, some aren’t

73
Q

How do the columns in the striate cortex differ?

A

in the orientation to which they respond best

74
Q

Adjacent columns usually have cells with:

A

slightly different orientation preferences

75
Q

What is the orderly pattern of the orientation columns occasionally interrupted by?

A

“color blobs”- columns of color-selective cells w center-surround receptive fields

76
Q

About how many orientation columns are here er group?

A

20, respond to a small area of the visual field

77
Q

How is the visual cortex divided?

A

into groups that respond to a small area of the visual field, so every part of the field is analyzed for stimuli

78
Q

To how many regions does the striate cortex project?

A

more than 40

79
Q

2 areas with different roles:

A

Parietal (“where”): nuclei about where things are relative to you and relative to each other, spatial aspects of the visual field

80
Q

Is the “where” or the “what” stream in the temporal lobe?

A

“what”

81
Q

in which lobe is the “where” stream?

A

parietal

82
Q

Where area:

A

almost completely dominated by cells related to moving objects, different types of movement that the where stream

83
Q

What does the “where” stream responds to?

A

circular or spiralling moves, visual flow (where you are going relative to the world), approaching or receding objects (egocentric)

84
Q

Lesion in the where stream:

A

loss of ability to perceive the speed and motion of objects in your environment (ie traffic), ability to use visual info to grasp objects, visual neglect in peripersonal space`

85
Q

Peripersonal space:

A

within arms reach

86
Q

T or F? AD can lead to fxnal deficits where you can’t find things close to you.

A

T

87
Q

Lesions of the “what” stream of the temporal cortex:

A

achromatopsia, can’t recognize colors

88
Q

Inputs that the what stream recognizes:

A

color selective cells or cells that respond to complex shapes, ie tools, houses

89
Q

The inability to perceive colors:

A

achromatopsia

90
Q

T or F? Some areas the “what” stream have many cells that are color selective and some that respond to complex shapes.

A

T

91
Q

What area of the brain is important for face perception?

A

The temporal cortex

92
Q

Aspects of face perception that the temporal cortex recognizes:

A

face orientation, expression, identity, gaze perception

93
Q

This area is particularly important for aspect of face perception:

A

fusiform face area

94
Q

Prosopagnosia:

A

face blindness

95
Q

Occipital (early visual stage) lesions:

A

can’t make sense of faces or distinguish bw pics of 2 different people

96
Q

Anterior tempoal lesions:

A

people understand the characteristics of the face, but can’t identify who they belong to

97
Q

Lesions of what side would lead to prosopagnosia:

A

R side lesions

Physiology (55 decks)

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