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Neuro Block 7 > The Visual System Part One > Flashcards

The Visual System Part One Flashcards

1
Q

Image on the retina

A

Inverted and reversed

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2
Q

Info from the upper visual space

A

Projected onto the lower retina

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3
Q

Info from the lower visual space

A

Projects to the upper retina

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4
Q

Right part of visual space

A

Projects to the left hemiretina in each eye and vice versa

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5
Q

Do the VF overlap

A

Yes most of it does, the minor peripheral zones do not

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6
Q

Outermost layer of the eye

A

Sclera

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7
Q

What is the sclera continuous with

A

Dura mater

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8
Q

How does the sclera continue posteriorly

A

As the sheath of the CN2

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9
Q

What begins at the limbus

A

Cornea

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10
Q

Vascularized middle layer

A

Choroid plexus (uvea)

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11
Q

Where is the choroid

A

Between the sclera and the retina

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12
Q

Pigment of the choroid

A

Densely pigmented

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13
Q

What is the principal route through which blood vessels and nerves travel within the wall of the eye

A

Choroid

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14
Q

What do choroid caps supply

A

Retinal photoreceptors

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15
Q

What does choroidal pigment do

A

Absorbs light

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16
Q

How does the choroid continue anteriorly

A

Dorms the bulk of the ciliary body

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17
Q

What is the choroid similar to

A

Arachnoid mater

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18
Q

What is the innermost layer of the eye

A

Retina

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19
Q

What part of the retina lies adjacent to the choroid

A

RPE

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20
Q

Where do the rods and cones point towards

A

The choroid, light must cross all layers of the retina to get to the photoreceptors

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21
Q

What are the layers of the retina from most superficial to deep (choroid to vitreous)

A
  1. Epithelial layer
  2. Photoreceptor cell outer and inner segments
  3. Outer limiting membrane
  4. Outer nuclear layer
  5. Outer plexiform layer
  6. The inner nuclear layer
  7. Inner plexiform layer
  8. Ganglion cell layer
  9. Nerve fiber layer
  10. Inner limiting membrane
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22
Q

Where are the nuclei of the photoreceptor cells

A

Outer nuclear layer

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23
Q

Where are the synaptic connections of photoreceptors with other retinal cells

A

Outer plexiform layer

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24
Q

Contains the somata of second order and some third order retinal cells

A

Inner nuclear layer

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25
Q

Another area of synaptic contact in the retina other than the outer plexiform layer

A

Inner plexiform layer

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26
Q

What part of retina contains the cell bodies of the ganglion cells

A

Ganglion cell layer

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27
Q

What layer of the retina is composed of the axons of the ganglion cells that converge at the optic disc to form the optic nerve

A

Nerve fiber layer

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28
Q

This layer of the retina consists of glial cell processes joined by tight junctions

A

Inner limiting membrane

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29
Q

This retinal layer is located between the nerve fiber layer and the vitreous

A

Inner limiting membrane

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30
Q

This layer is a single layer of polygonal, pigmented cells

A

Retinal pigment epithelium

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31
Q

How do the RPE cells support the photoreceptors

A

Metabolically

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32
Q

What are the two main roles of the RPE

A

Support the photoreceptors metabolically and they play a role in absorbing light

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33
Q

What direction do the rods and cones point

A

Towards the epithelial layer (and choroid)

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34
Q

Relative to the direction of light, how are the rods and cones positioned

A

Backwards

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35
Q

5mm diamter region in the center of the retina

A

Macula lutea

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36
Q

What kind of photoreceptors are in the macula

A

Both, but predominantly cones

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37
Q

What kind of photoreceptors are in the fovea

A

Cones ONLY

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38
Q

What is the central fovea specialized for

A

Vision of the highest acuity

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39
Q

What is different about the deep retinal layers in the foveal area?

A

They are pushed aside so that the cones are exposed. Light gets right to the cones

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40
Q

What receives inputs from individual foveal cones

A

Midget bipolar cells

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41
Q

What do the midget bipolar cells contact after receiving inputs from individual foveal cones

A

Individual midget ganglion cells, so that an anatomical basis for highly detailed foveal vision is maintained
1:1!!

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42
Q

smaller receptive field

A

Better VAs

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43
Q

The larger the receptive field

A

The harder it is to discern between 2 points, worse VA

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44
Q

What kind of photo receptors are in the optic disc

A

None. This is where the central axons of ganglion cells leave the eye to form the optic nerve

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45
Q

Where do the central axons of hte ganglion cells originate

A

At the border with the vitreous

46
Q

What must the central axons of ganglion cells do before passing through the sclera

A

Traverse the retina

47
Q

Where is the blind spot

A

Where the optic disc is

48
Q

Why is there a blind spot where the optic disc is

A

Because there are no photoreceptors there

49
Q

Are we aware of the blind spot at the optic nerve?

A

No, the nervous system simply fills it in. The other eye compensates in binocular vision

50
Q

Where does the density of the cones decrease sharply

A

Outside the fovea

51
Q

Where does the density of rods increase sharply

A

Outside the fovea, reaching a maximum use outside the macula

52
Q

What portion of the rods and cones are responsible for photoreception

A

The outer portions

53
Q

The process by which photons are detected and the information is transducer into an electrical signal

A

Photoreception

54
Q

What connects the outer segment to the inner segment of the photoreceptor and what does it contain

A

The ciliary. It contains mitochondria

55
Q

Where are the nucleus of the photoreceptor cells found

A

Outer nuclear layer

56
Q

Where do the photoreceptor cells terminate?

A

Outer plexiform layer in an expansion that makes synaptic contacts with neurons

57
Q

What is the synaptic expansion on the rod cells called

A

Spherule

58
Q

What is the synaptic expansion on the cone cells called

A

Pedicle

59
Q

What do the surface membranes of rods and cones outer segments contain

A

cGMP gated Na+ channels

60
Q

When are cGMP concentrations high

A

In the dark

61
Q

When are the Na channels open, allowing a current of Na+ ions to flow freely into the outer segment?

A

In the dark

62
Q

When are rods and cones depoalrized?

A

In the dark

63
Q

What do rods and cones release at a steady rate in the dark

A

Glutamate

64
Q

What does light induce in photoreceptors

A

Hydrolysis of gCMP, causing cation channels to close, the membrane hyperpolarizes, and transmitter release declines

65
Q

What are the G protein-coupled receptors of the rods and cones

A

Opsins (photopigments)

66
Q

What is the ligand of the receptor opsin

A

11-cis retinal (vit A derivative)

67
Q

What is the effect of light on the opsin and 11-cis retinal

A

It isomerizes 11-CIA retinal to all-trans retinal, which dissociates from opsin

68
Q

What does isomerized retinal do

A

Causes a conformational change in the opsin-opsin (trans) activates transducin (G protein)-transducin activates phosphodiesterase E (enzyme that hydrolyzes cGMP)-cGMP concentration decreases-Na channels close-secretion of glutamate stops

69
Q

When is 11-cis-retinal bound to opsins (rhodopsin)

A

Dark

70
Q

When does 11 trans retinal release from opsin and react with transducin?

A

In light

71
Q

How many types of opsins in cones

A

3

72
Q

How many types of opsins in rods

A

1

73
Q

What are the different cone opsins

A
  • L (red)
  • M (green)
  • S (blue)
74
Q

What is the absorption peak of each class of cones determined by

A

The kind of opsin a particular cone makes

75
Q

What kind of retinal do each of the cone opsins bind

A

They all bind 11-cis-retinal

76
Q

What is the basis of trichromatic color in humans

A

The 3 different cone opsins

77
Q

Which is more sensitive to light, rods or cones?

A

Rods

78
Q

What kind of light do rods respond to

A

Only up to about moonlight levels of light intensity

79
Q

What is the reaction time of rods

A

Slow

80
Q

What kind of specificity do the rods have?

A

Not very specific. Could take up to thousands of rods to generate signal

81
Q

Cone sensitivity

A

They have a smaller outer segment and less visual pigment. This makes them less sensitive

82
Q

What do cones require to function effectively

A

Greater level of illumination

83
Q

There is considerably less ______ in cone pathways than in rod pathways

A

Convergence

84
Q

What makes possible the huge resolution of fine spatial detail

A

There is less convergence in cone pathways than in rod pathways

85
Q

Where is acuity highest

A

Where midget ganglion cells have receptive fields with centers the size of a single cone (1:1!!)

86
Q

What kind of synapses can photoreceptor cells form with bipolar cells

A

Either excitatory or inhibitory

87
Q

Is glutamate release all or nothing?

A

No, it is gradual and depends on the amount of light

88
Q

Where do rod bipolar cells terminate

A

On processes of special amacrine cells, depolarizing them, and they in turn depolarize ganglion cells

89
Q

Portion of the VF where light causes excitation or inhibition of one retinal ganglion cell

A

Receptive field

90
Q

How are receptive fields determined

A
  • Photoreceptors respond to light in their respective fields and form excitatory or inhibitory synapses onto bipolar cells
  • bipolar cells, in turn, synapse onto ganglion cells, whihc send sons into the optic nerve
  • convey info RBC releasing NT in a graded fashion
  • ganglion cells fire APs as they convey info into optic nerve
91
Q

Are receptive fields yes or no

A

Yes

92
Q

Center surround receptive fields

A
  • composed of roughly circular zones
  • illumination of the central area causes an increase in firing rate, whereas illumination of the peripheral area has the opposite affect
  • this is an On-center OFF-surround receptive field
  • Off-center ON surround receptive fields also exist
93
Q

What has to happen for he ganglion cells in a receptive field to be activate

A

Has to have at least part of the off or part of the ON deactivated. If they are all illuminated or all under dim conditions they will cancel each other out

94
Q

Simultaneous illumination of both enter and surround causes what

A

Relatively little change in firing rate because the antagonistic effects of the two areas roughly cancel each other

95
Q

Contrast between the two different areas of the receptive fields

A

At the level of the ganglion cells, the contrast between the two is of paramount importance

96
Q

What is scotoma most often lay produced by

A

Lesions of the retina

97
Q

What does a scotoma represent

A

A visual field defect, single or multiple

98
Q

Likely causes of scotoma

A

Embolus, hemorrhage

99
Q

Amaurosis fugax and scotoma

A

Treat by rubbing the eyebulb to dislodge the embolus or at least move it forward to decrease the lesion size

100
Q

An inherited, degenerative disease that causes severe vision impairment due to the progressive degeneration of the rod photoreceptor cells in the retina

A

Retinitis pigmentosa

101
Q

What is responsible for the majority of autosomal-dominant inherited retinitis pigmentosa cases

A

Mutations in the rhodopsin gene disrupts the rod-opsin protein

102
Q

What is the temporal profile of retinitis pigmentosa

A

Insidious, progresses slow and steady

103
Q

What is the give away for retinitis pigmentosa

A

Tunnel vision

104
Q

Where are the genes for the red and green cone pigments

A

X chromosomes

105
Q

What can cause a red green color blindness

A

Unequal crossing over during meiosis can cause one X chromosome to wind up with a missing or defective red or green gene

106
Q

Lack of red pigment

A

Protanopia

107
Q

Lack of green pigment

A

Deuteranopia

108
Q

What percent of population is RGcolorblind

A

2% male population

109
Q

Lack of blue cone pigment

A

Rare because located on chromosome 7, equally uncommon in males and females

110
Q

Absence of red makes it difficult to see what colors

A

Red, yellow, and green objects

Neuro Block 7 (10 decks)

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