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Neuro Block 7 > Visual System 1 > Flashcards

Visual System 1 Flashcards

1
Q

The image on the retina is

A

Inverted and reversed

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2
Q

Right part of space projects to

A

Left hemiretina

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3
Q

Left part of space projects to

A

Right hemiretina

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4
Q

Most of the visual fields of the eyes

A

Overlap - there is only a minor peripheral zone that doesn’t overlap

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5
Q

Outermost layer of the eye

A

Sclera

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6
Q

Sclera is continuous with

A

Dura mater

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7
Q

What continues posteriorly as a sheath of the optic nerve

A

Sclera

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8
Q

Beginning at the circular transition zone called the limbus, the transparent ______ lets light into the eye

A

Cornea

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9
Q

Vascularized middle layer of the eye

A

Choroid (plexus?) aka uvea

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10
Q

Choroid is between

A

Sclera and retina

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11
Q

What is the principal route of travel for blood vessels and nerves in the eye

A

Choroid

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12
Q

Choroidal capillaries supply

A

Retinal photoreceptors

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13
Q

Choroidal pigment

A

Absorbs light

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14
Q

The urea continues anteriorly to form the bulk of the

A

Ciliary body and the stroma of the iris

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15
Q

Innermost layer of eye

A

Retina

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16
Q

What lies adjacent to the choroid?

A

RPE

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17
Q

Retinal detachment occurs if

A

Connection between choroid and RPE is not strong

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18
Q

Retinal cells are metabolically dependent on what

A

Pigmented epithelial cells and adjacent choroidal vasculature

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19
Q

Retinal layers (sup to deep)

A
  1. epithelial
  2. photoreceptor outer and inner
  3. Outer limiting membrane
  4. Outer nuclear layer
  5. Outer plexiform layer
  6. Inner nuclear layer
  7. Inner plexiform layer
  8. Ganglion cell layer
  9. Nerve fiber layer
  10. Inner limiting membrane
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20
Q

Outer nuclear layer

A

Consisting of the nuclei of photoreceptor cells

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21
Q

Outer plexiform layer

A

Consisting of the synaptic connections of photoreceptors with other retinal cells

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22
Q

Inner nuclear layer

A

Containing somata of 2nd and some 3rd order retinal cells

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23
Q

Inner plexiform layer

A

Layer of synaptic contact

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24
Q

Ganglion cell layer

A

Containing the cell bodies of ganglion cells

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25
Q

Nerve fiber layer

A

Composed of the axons of the ganglion cells. These axons converge at the optic disc to form the optic nerve

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26
Q

Inner limiting membrane

A

Located between the nerve fiber layer and the vitreous. The limiting membranes consist of glial cell processes joined by tight junctions

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27
Q

Cell type of RPE

A

Single layer of polygonal pigmented cells

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28
Q

One side of each RPE cell joins the

A

choroid - to supply the avascular first 2 layers of the retina

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29
Q

Pigment epithelial cells of the RPE support photoreceptors

A

Metabolically

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30
Q

Pigment epithelial cells of the RPE play a role in

A

Absorbing excess light that has passed through the retina

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31
Q

Rods and cones point

A

TOWARDS the epithelial layer -> BACKWARDS to the direction of light

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32
Q

Yellow structure located in the central retina, about 5mm diameter, with predominantly cones

A

Macula

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33
Q

Structure located in the center of the macula that is about 1.5mm in diameter that consists of ONLY cones

A

Fovea

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34
Q

Which structure has only cones?

A

Fovea

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35
Q

What part of the fovea is specialized for vision of the highest acuity?

A

Central

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36
Q

Specialized interneurons called ______ receive their input from individual foveal cones

A

Midget bipolar cells

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37
Q

Midget bipolar cells contact _____ so that an anatomical basis for highly detailed foveal vision is maintained

A

Midget ganglion cells

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38
Q

No photoreceptors are present where

A

Optic disc

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39
Q

Location where central axons of ganglion cells leave the eye to form the optic nerve

A

Optic disc

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40
Q

Central axons of ganglion cells originate where

A

At the border with the vitreous, so they must traverse the retina before passing through the sclera

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41
Q

Blind spot

A

Exists because there are no photoreceptors at the optic disc, so we are blind to any object whose image falls on this part of the retina

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42
Q

Why are we unaware of our blind spot?

A

The brain fills it in for us and the other eye compensates in binocular vision

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43
Q

Density of cones decreases sharply where?

A

Outside the fovea

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44
Q

Density of rods increases and reaches a maximum where?

A

Just outside the macula

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45
Q

Which part of the eye is used for high-acuity color vision in reasonably bright light?

A

Fovea

46
Q

What part of rods and cones are responsible for photoreception?

A

Outer portions

47
Q

Photoreception

A

The process by which photons are detected and the information is transduced into an electrochemical signal

48
Q

The ______ connects the outer segment to the inner segment

A

Cilium

49
Q

Which part of a photoreceptor contains mitochondria?

A

Inner segment

50
Q

Spherule

A

Part of a rod that terminates in the outer plexiform layer in an expansion that makes synaptic contacts with neurons

51
Q

Pedicle

A

Part of a cone that terminates in the outer plexiform layer in an expansion that makes synaptic contacts with neurons

52
Q

Surface of rods and cones contain

A

cGMP gated Na+ channels

53
Q

In the dark

A

cGMP concentration is high and channels are open, Na current flows freely into the outer segment
DEPOLARIZED

54
Q

Rods and cones are depolarized when/where?

A

In the dark

55
Q

Glutamate is released at a steady rate when

A

The rods and cones are depolarized (in the dark)

56
Q

In the light

A

cGMP hydrolysis causes channels to close and transmitter release declines
HYPERPOLARIZED

57
Q

Glutamate is not released when/where?

A

In the light

58
Q

Opsins (photopigments)

A

G protein coupled receptors of the rods and cones

59
Q

Ligand of opsin

A

11-cis retinal (vitamin A derivative)

60
Q

What does light do to 11-cis retinal?

A

Isomerize it to all-trans retinal, which DISSOCIATES from opsin

61
Q

Isomerize retinal causes a conformational change in the opsin ->

A

opsin (trans) activates transducin, a G protein -> transducer activates phosphodiesterase E, an enzyme that hydrolyzes cyclic guanosine monophosphate (cGMP) -> cGMP concentration decreases -> Na+ channels close -> secretion of glutamate stops

62
Q

Types of cones

A

Long (L), middle (m), and short (S)

63
Q

Long-wavelength cones

A

Red

64
Q

Middle-wavelength cones

A

Green

65
Q

Short-wavelength cones

A

Blue

66
Q

Absorption peak of a cone is determined by

A

The kind of opsin a particular cone makes

67
Q

______ respond only up to about moonlight levels of light intensity

A

Rods

68
Q

______ responses are slow

A

Rod

69
Q

The responses of multiple ______ must be pooled to produce firing of ganglion cells in response to dim light

A

Rods

70
Q

In the peripheral retina

A

Outputs of thousands of rods converge on hundreds of bipolar cells before ultimately reaching single ganglion cells, hence spatial resolution in dim light is relatively poor

71
Q

Can rods differentiate color? Why?

A

No - they all contain the same rhodopsin

72
Q

Rods rhodopsin absorb what wavelength of lifer most effectively

A

500nm

73
Q

Cones have ______ outer segments and ______ visual pigment

A

Smaller

Less

74
Q

Which is more sensitive, rods or cones?

A

Cones

75
Q

There is considerably less convergence in ______ pathways than ______ pathways

A

Cone

Rod

76
Q

Acuity is highest

A

Where the midget ganglion cells have receptive fields with centers the size of a single cone

77
Q

In the absence of light, rods and cones

A

RELEASE glutamate

78
Q

Glutamate release is

A

all or nothing, gradual, and depends on the amount of light

79
Q

Photoreceptors form either excitatory or inhibitory synapses with ______ cells

A

Bipolar

80
Q

Rod bipolar cells terminate

A

On processes of special amacrine cells, DEPOLARIZING them

81
Q

Amacrine cells depolarize

A

Ganglion cells (1st order neurons of the optic nerve)

82
Q

Through their connections with ______ cells, photoreceptors may excite or inhibit adjacent cells

A

Horizontal

83
Q

Receptive field

A

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

84
Q

Photoreceptors and bipolar cells convey information by

A

Releasing neurotransmitter in a graded fashion that depends on membrane potential

85
Q

Ganglion cells fire action potentials as they convey information to the

A

Optic nerve

86
Q

Ganglion cells have ______ receptive fields

A

Center-surround

87
Q

Ganglion cell receptive fields are composed of

A

Two concentric, roughly circular zones

88
Q

Illumination of the central area of the ganglion cell receptive field causes

A

Increase in firing rate

89
Q

Illumination of the peripheral (surround) area of the ganglion cell receptive field causes

A

Decrease in firing rate

90
Q

Ganglion cell receptive field is an ___-center ___-off surround receptive field

A

ON-center OFF-surround

91
Q

Simultaneous illumination of both the center and surround causes

A

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

92
Q

At the level of the ganglion cells, the contrast between the areas of the receptive field is of ______ importance

A

Paramount (high!)

93
Q

Scotoma is most often produced by lesions of the

A

Retina

94
Q

Scotoma represents

A

Visual field defects - single or multiple

95
Q

Most likely dx of scotoma

A

Embolus arising from the internal carotid artery resulting in a branch retinal artery occlusion

Other possible causes are hemorrhage or a disorder of the optic nerve

96
Q

Patient with amaurosis fugax (sudden blindness) should be treated with

A

Massage of the eyebulb to dislodge the embolus or at least move it forward to decrease the lesion size

97
Q

Retinitis pigmentosa

A

Inherited disease (AD,AR, X-linked, and mitochondrially defined) degenerative eye disease that causes severe vision impairment due to progressive degeneration of the rod photoreceptor cells in the retina

98
Q

Most common cause of autosomal-dominant RP cases

A

Mutations in the rhodopsin gene, which disrupts the rod-opsin protein

99
Q

DX of RP occurs

A

Anywhere from early infancy to late adulthood

100
Q

Early stages of RP

A

Compromised peripheral and dim light vision

101
Q

Later stages of RP

A

Abnormalities in the adjacent retinal pigment epithelium and deterioration of cone photoreceptor cells

102
Q

Give away phrase for RP?

A

Tunnel vision and eventual blindness

103
Q

Genes for red and green cone pigments are located next to each other on the X chromosome, and unequal crossing over during meiosis can cause one X chromosome to wind up with a missing or defective

A

Red or green gene

104
Q

What percent of male population is colorblind?

A

2%

105
Q

Why aren’t females often colorblind?

A

They likely have an X chromosome with normal red green cone pigments since they have 2 X chromosomes

106
Q

Lack of the blue cone pigment is

A

Rare, and equal in males and females because the gene is located on chromosome 7

107
Q

Absence of the cone population that absorbs in the ______ makes it difficult to discriminate among red, yellow, and green objects

A

Red

108
Q

Protanope

A

Loss of red

109
Q

Deuteranope

A

Loss of green

110
Q

Tritanope

A

Loss of blue

Neuro Block 7 (8 decks)

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