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Neuroscience Block 3 > Vision > Flashcards

Vision Flashcards

0
Q

From what structure does the eye develop?

A

Out-pouching of the diencephalon called the optic disk

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1
Q

What are the three layers of the eye?

A

Sclera, choroid, retina

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2
Q

What layer of the eye is part of the CNS?

A

The retina, so you can use an ophthalmoscope to check for CNS problems

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3
Q

What is phototransduction?

A

The process by which light impinges on the retina and is converted to a neutral signal (graded response)

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4
Q

What are the layers of the retina from outermost to innermost?

A
  1. Pigmented epithelium
  2. Photoreceptors cells (outer segment, outer nuclear layer, outer plexiform layer)
  3. Bipolar and horizontal cells (inner nuclear layer, inner plexiform layer)
  4. Ganglion cell layer
  5. Nerve fiber layer
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5
Q

What occurs in the outer segment of the photoreceptors layer?

A

Detection of light occurs

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6
Q

What is the outer nuclear layer of the retina?

A

The nuclei of the photoreceptors

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7
Q

What occurs in the outer plexiform layer of the retina?

A

Photoreceptors synapse with bipolar and horizontal cells

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8
Q

What is the inner nuclear layer of the retina?

A

The cell bodies (soma) of the bipolar and horizontal cells

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9
Q

What occurs in the inner plexiform layer of the retina?

A

The axons of bipolar cells synapse with the dendrites of ganglion cells.
Amincrine cells make lateral connections at the bipolar/ganglion synapses

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10
Q

Where are Amincrine cells found?

What cell is it analogous to (only in a different layer)

A

In the inner plexiform layer connecting to the bipolar/ganglion synapses (horizontal connections like the horizontal cells in the outer plexiform layer)

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11
Q

Ganglion cells project their neurons through what layer to end up where?

A

Axonal processes travel through the nerve fiber layer to exit the eye at the optic disc to form the optic nerve.

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12
Q

Do the chemical synapses in the retina generate action potentials?
Why or why not?

A

They operate throughout graded responses because the signal is traveling such a short distance (250 microm) there is no need to waste energy on an AP

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13
Q

What is the path of light into the retina?

A

It travels through the nerve fiber, ganglion cell, inner plexiform, inner nuclear, outer plexiform, outer nuclear, to the photoreceptors outer segment where the light is detected.
A graded response travels back through all those layers until the ganglion cell and then an AP is generated

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14
Q

What are the 2 classes of photoreceptors and 4 classes of neurons in the retina?

A

Photoreceptors : rod and cone

Neurons: bipolar, horizontal, Amincrine, ganglion

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15
Q

How many mV is the typical graded response in the retina?

A

40mV

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16
Q

In the dark, what is the membrane potential?

What happens when there is a brief flash of light?

A

-40 mV (relatively depolarized)

When there is a flash of light, there is a transient hyperpolarization (graded)

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17
Q

How is the membrane potential of the photoreceptor measured?

A

It is impaled with a Microelectrode and the voltage response can be measured?

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18
Q

What organelle is prominent in the cell body of a photoreceptor cell?
What does this tell us about photoreceptors?
What does this make the photoreceptor sensitive to?

A

Mitochondria which tells us that photoreceptors are metabolically active.
Because the mitochondria rely on oxygen, the photoreceptor cells are particularly sensitive to ischemia

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19
Q

What happens if you shine a flask of light on the axon of a photoreceptor cell?

A

Nothing! The photoreceptor outer segment is the part of the photoreceptor that detects light!

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20
Q

In the dark, what is the direction of current? What ions are involved?

What happens when there is a flash of light?

A

There is a net inward current of Na and Ca.

The light reduces Na and Ca current by closing a cGMP-gated channel to close. So the voltage of the cell is now determined by the net movement of K out of the cell (hyperpolarize)

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21
Q

Why does flashing light on a photoreceptor cause hyperpolarize tin?

A

The light closes a cGMP-gated channel reducing the inflow of Na and Ca into the cell. The net flow of current is now determined by K flowing out (hyperpolarization)

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22
Q

If you increase the duration of the flash of light on the retina, what happens to the membrane potential?

A

The amplitude of the hyperpolarization and the time it takes to depolarize back to -40mV both increase

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23
Q

What happens to the photopigments in rods and cones when they are exposed to light?
What are photopigments compromised of?

A

They undergo molecular rearrangement.

They are comprised of 11-cis retinal covalently bound to an opsin

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24
Q

What is an opsin?

How are the opsin of rods and cones different?

A

Opsin is a g-coupled membrane receptors in the outer disc of the retina
Rods use rhodopsin
Cones use different opsins designed to absorb different ranges of the color spectrums (long opsin-red, medium opsin- green, short opsin-purple/blue)

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25
Q

When is retinal capable of acting as a ligand for the opsin g-protein coupled receptor?

A

When light converts 11-cis retinal to all-trans retinal (photoisomerization)

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26
Q

What is the primary source of retinal?

A

B-carotene in the diet

It is cleaved to all trans retinal which can then be reduced to retinol (vitamin A )

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27
Q

What are opsins coupled to?

A

Transducin (heterotrimeric G-protein)

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28
Q

What is the signal cascade from light–>

six steps

A
  1. Light changes 11-cis retinal to all trans retinal which acts as a ligand for the opsin.
  2. The opsin triggers the exchange of GDP with GTP and releases the alpha subunit of the Transducin.
  3. The alpha subunit activates phosphodiesterase (PDE)
  4. PDE hydrolyzes cGMP to GMP
  5. Decreased cGMP favors closed state of the cGMP-gated channel (Na and Ca channel)
  6. Membrane potential hyperpolarizes toward Ek because the outward K channel is still open
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29
Q

What is the purpose of the retina using g-protein coupled receptors?

A

Large amplification of signal during transduction

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30
Q
  1. In the rod, how many photons are required to isomerize an 11-cis retinal?
  2. Once the rhodopsin is activated, how many Transducin alpha subunits are released?
  3. How many PDE can each alpha Transducin activate?
  4. How many cGMP can each PDE hydrolyze?
  5. How many channels close?
  6. How much would the cell hyperpolarize by?
A
  1. 1 photon-> one all trans retinal-> one rhodopsin
  2. One rhodopsin-> 800 alpha Transducin GTP subunits
  3. Each alpha subunit-> one PDE
  4. Each PDE -> 6 cGMP
  5. 200 cGMP gates close
  6. mV hyperpolarizes by 1mV
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31
Q

In order to have amplification of signal in the retina, what is compromised?

A

Speed

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32
Q

Which is more sensitive to light photons, rods or cones?

A

Rods need one photon to close 200 channels and hyperpolarize by 1mV

Cones require 100 photons to reduce the mV by 1mV

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33
Q

What are the roles of the retinal pigment epithelium (RPE)? (2)
What are the six steps to carry out the primary role?

A

The primary function is that It recycles retinal that has been converted to all-trans retinal.
The second function is that it phagocytoses old discs that have migrated distally in the outer segment and were shed

  1. The all trans retinal dissociates from the opsin
  2. It is reduced to all trans retinol
  3. All trans retinol crosses the membrane and binds to IRBP (binding protein)
  4. IRBP-retinol is endocytosed by RPE
  5. RPE converts it to 11-cis and oxidized it to retinal
  6. IRBP shuttles it back to bind with the opsin
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34
Q

What is the lifetime of a disc in the outer segment of the retina?

A

12 days as shown by metabolic labeling

They move more and more distally in the outer segment, are shed and then the debris is phagocytosed by RPE.

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35
Q

How are rods and cones structurally different?
(length, shape, disc configuration in outer segment)
How are they similar?

A

Rods are longer and the discs are stacked as intracellular membrane-bound organelles
Cones are tapered in the more distal outer segment and opsins are in the invaginations rather than in intracellular discs

They both contain abundant mitochondria because of the high metabolic demand for transduction

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36
Q

Where is rhodopsins peak absorbance?

What does this allow it to detect?

A

Blue-green wavelength between the cones s-opsin and m-opsin.

This allows rhodopsin to distinguish light intensity but not color

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37
Q

What is the most abundant cone opsin?

A

L then M then S

We have the highest frequency of red light receptors

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38
Q

What is the main cause of color-blindness?
Why is it more common to have red/green?
Why is it more common in men?

A

The L and M opsin genes are close on the X-chromosome and due to their high conservation, there is frequent crossover deletion and duplication.

This makes red/green color blindness the most common in men (because they only have one x so less chance for the genes on the other X to take over)

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39
Q

What is it called when there is unequal crossing over in the region where the L and M opsin genes are and one of the offspring X is left without green opsin?

A

Deuteranopia (red/green color blindness)

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40
Q

Where is the highest concentration of cones on the retina?

A

The fovea- a region in the center of the retina where there are no capillaries or structures which allow for max spatial resolution (acuity)

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41
Q

Why does the fovea allow for maximum spatial resolution?

A

There are no capillaries or other structures in the way

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42
Q

How do the distribution of rods and cones differ as you move from the fovea?

A

The number of cones decreases and the amount of rods increases.
Central color vision is in bright light (photopic vision)
Peripheral monochromatic night vision is for dim light (scotopic vision)

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43
Q

What is the ratio of rods to cones on the retina?

A

100:1

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44
Q

What is photopic vision?

What is scotopic vision?

A

Central Color vision in bright light

Peripheral monochromatic night vision in dim light

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45
Q

Why are rods more sensitive to low light?

A

Low light has fewer photons.
Cones require more photons to activate so they drop out first
Your spatial resolution decreases, but your peripheral vision improves because the rods depolarize and are more acute in low light

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46
Q

What is retinitis pigmentosa?

What are the symptoms?

A

Degeneration and progressive loss of rods over decades

Symptoms: poor vision in low light, “night blindness”, restricted peripheral vision

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47
Q

What is the difference in kinetics of rods and cones when exposed to a brief flash of light?

A

Cones have a brief transient response

Rods have a sustained response that lengthens as the intensity of the light increases

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48
Q

How many rods converge on a bipolar cell? What does this allow?

How many cones converge on a bipolar cell? What does this allow?

A

Up to 100 rods can converge on one bipolar cell allowing increased sensitivity in low light but with decreased spatial resolution

One cone per bipolar cell allows optimized spatial resolution

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49
Q

What is the receptive field of a neuron?

What is the receptive area of the ganglion cell?

A

It is the region of the body that elicits an action potential when appropriately stimulated.
The ganglion cell receptive field is defined as the location on the retina that elicits a change in firing when stimulated by light

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50
Q

What are the two types of response cells for the receptive field?
How do they differ?
How do the two cell types response fields occur spatially?

A

ON-cell has increased firing when illuminated
OFF-cell reduces firing rate when illuminated but have a burst of spikes when the stimulus is turned off

There are equal numbers of on and off cells and they have overlapping receptive fields but on cells are more centrally located and off cells tend toward the periphery OR off cells are more central and on cells are to the periphery

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51
Q

What response is stimulated if the light is shined outside of the receptive field?

A

None.

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52
Q

Retinal ganglion cells respond most vigorously to differences in light level between what?

A

The center versus the surround

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53
Q

How does the size of receptive field vary with distance from the fovea?

A

Receptive field is small (0.1 degree) for ganglion cells in the fovea because spatial resolution needs to be high

In the periphery there is a lot of convergence of rods onto one bipolar cell resulting in receptive fields up to 10 degrees

54
Q

If you shine a dark spot onto the center of an ON-centered cell, what will occur?
When you remove the dark spot, what happens?

A

The signal decreases significantly.
When the dark spot is removed, it will rapidly fire because it will seem like it is sensing “light stimulus” (the removal of dark)

55
Q

If you shine a dark spot on an OFF-centered retinal ganglion, what will occur?
What happens when the dark spot is removed?

A

It will rapidly fire because it is responding to dark. When the light is removed, it will cease firing because it seems as if it is a transient light stimulus.

56
Q

If you have an ON-centered retinal ganglion what happens if you:

  1. Shine a light on the center
  2. Shine a light on the whole receptive field
  3. Turn off all the light
A
  1. Increased firing (very rapid)
  2. Modulated, steady firing (less rapid)
  3. Decreased firing
57
Q

If you have an OFF-centered retinal ganglion cell what happens if you:

  1. Shine a light in the center
  2. Shine a light on the whole receptive field
  3. Remove the light stimulus
A
  1. Firing will decrease
  2. Firing will increase to a modulated steady rate
  3. Firing will increase rapidly
58
Q

Why does firing rate get smaller when the center and surround are illuminated versus just illuminating the center?

A

The excitation of the center is offset by the inhibition of the surround
OR
The inhibition of the center is offset by the excitation of the surround

59
Q

What do photoreceptors release in high amounts in the dark state?
What level of the retina is this release occurring?
What two cells are involved in the synapse where it is released?
For this reason, would OFF-centered or ON-centered response be more expected?

A

Glutamate- major excitatory transmitter of the brain

The outer plexiform layer

The photoreceptor cell and bipolar cells

Off center response would be more expected because light would reduce glutamate, reducing excitation of the bipolar cell

60
Q

What cell determines whether ON or OFF behavior will occur?

A

The bipolar cell

61
Q

What receptors are expressed by ON-centered bipolar cells?

Why does this allow light (reduced glutamate) to be excitatory?

A

mGluR6 which when bound to glutamate CLOSE a cGMP-gated Na and Ca channel
“sign-inversion” receptor
(dark=high glutamate=more closed channels= less firing)
(light=low glutamate=more open channels=depolarized)

62
Q

For OFF-centered bipolar cells, what are the receptors?

A

AMPA and kainate receptors which are excited by glutamate.

dark=more glutamate= depolarization= excitatory signal
(light=less glutamate=hyperpolarization= inhibition)

63
Q

What receptors are on the ganglion cell where it synapses with the bipolar cell?
Are these excitatory or inhibitory?

A

AMPA/kainate/NMDA

Excitatory

64
Q

What happens to the cone when it is exposed to light?
What does this do to the on-centered retinal cell?
What does this do to the off-centered retinal cell?

A
  1. It hyperpolarizes-> reduces glutamate release
  2. On-centered mGluR6 are less inhibited -> excited by light
  3. Off-centered AMPA/kainate are less excited ->inhibited by light
65
Q

Where does sign inversion occur for ON-cells?

A

At the synapse between photoreceptor cells and bipolar cells expressing mGluR6 receptors

66
Q

What does surround inhibition allow us to do?

A

Detect edges and lines (increased visual acuity)

67
Q

What type of input do horizontal cells receive from photoreceptor cells?
What level of the retina do they receive this input?

What output do horizontal cells send? To what cells?
What is this process called?

A

They receive excitatory glutaminergic input in the outer plexiform layer
The output is GABA inhibitory signals as feedback to photoreceptors
This is called lateral inhibition because one cell inhibits its neighbors on either side creating surround inhibition (line/edge)

68
Q

What cells are involved in lateral inhibition?
What does lateral inhibition help us achieve?
Does it generate an action potential or rely on graded response?

A

Horizontal cells are excited by photoreceptors and then have inhibitory GABA synapses on the neighboring photoreceptor cells.

This allows for surround inhibition which allows us to detect edges and lines.

Graded response (the only cell in the retina that generates an AP is the ganglion cell)

69
Q

What are the two well recognized effects of lateral inhibition on the processing of visual information?

A
  1. Amplifies local differences of photoreceptor illumination in the output of bipolar cells (enhances visual edge)
  2. Adaption to background levels of illumination extending the range of perception of brightness levels
70
Q

What do horizontal cells do to the magnitude of the bipolar cell response for simultaneous increased light to both rods?
What is the effect of one of the rods receive light and the other dark?

A

If both rods are receiving light, the horizontal cell does not change to magnitude of the bipolar cell response significantly
If one rod receives dark and the other receives light, the bipolar cell response is greatly Amplified. (edge detection)

71
Q

In the oblique dark/light boundary test, why are the responses for “all dark” and “all light” not that different?

A

Because the center and surround offset each other modulating the voltage response in all light or all dark.
“summative cancellation”

72
Q

On the oblique dark/light boundary test, what happened to the cells with partial shading?

A

If it was majority in the dark, it was exaggeratedly inhibited
If it was majority in the light, it was exaggeratedly excited
If it was half in light, half out of light, there was enhanced detection for the location of the boundary

73
Q

What happens to the cellular response of a cell if there is no inhibitory surround?

A

As the cell moves from dark to light, there is a steady increase of cellular response. (no variation or line detection)

74
Q

How are we able to see over a huge range of light levels?

A

The different sensitivities of rods and cones to light.
Each photoreceptor has a response range of 10000 and with overlap, a 10,000,000 range.

Dim- rods- scotopic- poor visual acuity and color detection
Medium light- rods and cones- mesopic
Bright- cones- photopic- high acuity and color detection

75
Q

How do we adapt when a steady level of background stimulation has been present for a long time?

A

The response curve shift so the background level is now the midpoint of the response
This allows sensitivity (steepness) to be optimized for increases or decreases in the stimulus

76
Q

What two factors allow sensory adaptation of the response curve to sustained stimulus on the retina?

A
  1. Horizontal cell surround inhibition

2. Shifts in photoreceptor response as a consequence of Ca signaling

77
Q

How does Ca level help sensory adaptation in the retina?

What are the three main things low intracellular Ca does?

A

Increased light-> decreased cGMP-> closed cGMP channels -> decreased Ca influx -> low intracellular Ca

Several regulatory enzymes for phototransduction are Ca dependent so low Ca:

  1. Increases affinity of the channel for cGMP
  2. increases guanylate cyclase activity
  3. Increases rhodopsin kinase activity (reducing PDE)

so there is a net decreased response in sustained light

78
Q

What does it mean that images are flipped as they project onto the retina?

A

Image from the superior visual field project onto the inferior half of the retina.
Images from the left visual field project onto the right half of the retina

79
Q

What is the projection pathway of the retino-geniculo-calcarine pathway?
What kind of vision is this responsible for encoding?

A

Retina to lateral geniculate nucleus to primary visual cortex.
The retino-geniculo-calcarine pathway is responsible for conscious visual perception

80
Q

When do retinal ganglion cell axons become myelinated?

A

After they penetrate the sclera of the eyeball, they associate with oligodendroglial cells and acquire a myelin sheath.

81
Q

What do optic discs lack that make them sites of function “blind spots”?

A

Photoreceptors or retinal neurons

82
Q

What part of the nervous system is the optic nerve a part of?
What is the subarachnoid space around the optic nerve continuous with?

A

CNS so it is invested externally by dura and arachnoid mater.
The subarachnoid space around the nerve is continuous with the subarachnoid space of the brain

83
Q

What is papilledema?

What causes it?

A

Swelling of the optic disc visible with the ophthalmoscope (appears blurry rather than sharp edged)
It is causes by increased cranial pressure transmitted to the optic nerve by the subarachnoid space continuous with the brain covering

84
Q

What axons form the optic chiasm?

A

Ganglion cell axons from the nasal portion of each retina (temporal visual field) cross to form the optic chiasm.

85
Q

What ganglion cell axons cross to run contralaterally?
Which ganglion cell axons remain ipsilateral?

When these axons join, what do they form?

A

The ganglion axons from the nasal portion of the retina cross in the optic chiasm

The ganglion axons from the temporal portion of the retina remain ipsilateral.

The contralateral nasal portion and ipsilateral temporal portion join to form the optic tract.

86
Q

Your central field of vision projects onto what part of the retina?

Your peripheral vision projects onto what part of the retina?

A 
Central vision (nasal field) projects onto the temporal retina ganglion cells. 
These fibers remain uncrossed and stay ipsilateral

Peripheral vision (temporal) project onto the nasal retina, cross in the optic chiasm and go to the contralateral lateral geniculate nuclei.

87
Q

Where is the lateral geniculate nucleus found?
What is its distinguishing physical feature/why?
How many layers is the lateral geniculate?

A

Just above the hippocampus.
It appears dark brown because of the accumulation of lipofuscin granules.
Six layers numbered ventrally to dorsally.

88
Q
  1. To what layers of the lateral geniculate do ipsilateral (temporal) retinal projections synapse?
  2. To what layers of the lateral geniculate do contralateral (nasal) retinal projections synapse?
A
  1. Layers 2,3,5

2. Layers 1,4,6

89
Q

Which layers of the lateral geniculate contain large neurons (magnocellular layer) and from what cells do they receive signal?

Which layers contain the smaller neurons (parvocellular layer) and from what cells do they receive signal?

A
  1. Layers 1,2 receiving signal from magnocellular retinal ganglion cells
  2. Layers 3,4,5,6 receiving signal from parvocellular retinal ganglion cells
90
Q

What are the functional differences between parvocellular and magnocellular levels of the lateral geniculate?

A

M neurons respond to movement, location and contrast (WHERE)

P neurons process color, form, and visual acuity (WHAT)

91
Q

Is signal to the lateral geniculate from the retinal ganglion cells convergent or divergent?

A

Both

92
Q

The magnocellular system sends projections to the area of the primary visual cortex responsible for what?

The parvocellular system sends projections to the area of the primary visual cortex responsible for what?

A
  1. Movement and contrast

2. Color and fine structural detail

93
Q

What is the ratio of reciprocal projections to the lateral geniculate FROM the primary visual cortex to initial projections from the lateral geniculate TO the primary visual cortex?
What is the function of the reciprocal projections?

A

2:1

Unknown

94
Q

What are the koniocellular layers of the lateral geniculate?

A

Lie between the major layers of the lateral geniculate and are responsible for shorter wavelength energy (blue light)

95
Q

What are the tracts that travel directly to the primary visual cortex from the lateral geniculate?

A

Optic radiations

96
Q

To Where does information from the superior retina travel?

Through what tract? Where is this tract mostly located?

A

Travel to the medial occipital lobe through the superior optic radiation (a white matter tract that lies predominantly in the parietal lobe)

97
Q

To where does information from the inferior retina travel?

Through what tract?

A

Information from the inferior retina travel to the occipital lobe through Meyer’s loop which sweeps in a curved path through the temporal lobe (the inferior optic radiation)

98
Q

Which path is more direct: superior optic radiation or inferior optic radiation?

A

Superior is more direct.

Inferior optic radiation goes through Meyers loop

99
Q

A lesion in the temporal lobe would result in what vision loss?

A

The inferior optic radiation travels through the temporal lobe so there would be loss of vision from the contralateral superior visual field (which projects onto the inferior retinal cells)

“pie in the sky deficit”

100
Q

A lesion to the parietal lobe would cause what visual deficit?

A

Contralateral loss of vision from the inferior visual field because the superior optic radiation would be disrupted

101
Q

What are the three names for the primary visual cortex?

A

Calcarine cortex
Striate cortex- because of myelin rich band in layer 4 dividing cortex into superficial and deep layers
Brodmann area 17

102
Q

What divides the primary visual cortex into superficial and deep layers?

A

Myelin rich bands in layer 4 (gennari’s line)

103
Q

In what layer do axons from the lateral geniculate nucleus synapse on the visual cortex?
What type of input does this layer receive?

A

Layer 4 (receptor for subcortical sites in the neocortex)

Monocular input- either from the ipsilateral eye OR contralateral eye, but not both

104
Q

How is the primary visual cortex arranged?

A

In a series of repeating, vertically oriented modules that are composed of vertically oriented columns of neurons

105
Q

What is ocular dominance?

Where is ocular dominance strongest?

A

The vertically oriented column of neurons in the primary visual cortex’s modules will respond preferentially to a particular signal. Some columns prefer ipsilateral input which others respond to contralateral projections.

It is strongest by the center of the column and fades as we move out

106
Q

What is meant by graded transition when referring to visual columns in the primary visual cortex?

A

Centers of “monocular” visual columns are separated from each other by “binocular” cells (receive ipsilateral and contralateral stimulation)

As you move from one monocular visual column to the next, there is a transition of columns receiving input exclusively from one eye to columns receiving input exclusively from the other eye.

107
Q

What two kinds of columns are the striate cortex divided into?

A
  1. Ocular dominance columns

2. Vertical orientation columns

108
Q

What do orientation columns respond to in the primary visual cortex?

A

Stimuli presented in a particular orientation (horizontal, vertical)
A graded transition exists between these columns just like there is between the ocular dominance columns

109
Q

Interplay between what two factors determines normal binocular vision?

A

Ocular dominance columns and orientation columns

110
Q

When are synaptic connections established in the primary visual cortex and extrastriate cortex?

A

During a very limited time interval in postnatal life

111
Q

What Brodmann areas are associated with the extrastriate cortex?

A

18 and 19

112
Q

Information concerned with movement, contrast, and orientation (magnocellular) relay to areas _______________ to the primary visual cortex.

A

Dorsal, like the parietal lobe

113
Q

Information concerned with color, form, object recognition (parvocellular) relay predominantly to areas _____________ to the striate cortex.

A

Ventral, like the temporal lobe

114
Q

Magnocellular and parvocellular streams of info have extensive reciprocal connections to what area?

A

The pulvinar nucleus of the thalamus

115
Q

A patient comes in complaining of being able to see cars, but they cant see the movement of the cars. (dangerous!)
What is the lesion they have probably disrupting?

A

The magnocellular stream in the dorsal projections from the primary visual cortex to the parietal lobe

116
Q

What visual deficit would be associated with a lesion in the right optic nerve?

A

The nasal retinal fibers haven’t crossed yet, so you would see a loss of all vision in the right eye (monocular blindness)

117
Q

What visual deficit would be associated with a lesion in the optic tract?

A

You would lose both temporal fields of vision because the axons of the nasal retina would be cut.
This is called bitemporal hemianopsia

118
Q

What lesion is monocular blindness associated with?

A

A lesion to the optic nerve

119
Q

What is bitemporal hemianopsia?

What lesion is it associated with?

A

The patient has no vision in either temporal field.

It is associated with a lesion in the optic chiasm

120
Q

What deficits would you find associated with a lesion in the right optic tract or right lateral geniculate?

A

You would lose vision from the ipsilateral nasal field of vision (temporal retinal axon) and the contralateral temporal visual field (nasal retinal field)
So you would lose central vision from your right eye and peripheral from your left (left visual field of each eye)
This is called left (contralateral) homonynous hemianopsia.

121
Q

What is contralateral homonynous hemianopsia?

What lesion is it associated with?

A

It is the loss of one side of vision from each eye.
A lesion to the right optic tract or right lateral geniculate would cause a loss of the left visual field from each eye (right nasal, left peripheral)

122
Q

What visual deficit would be associated with a lesion to the left inferior optic radiation (Meyers loop in the temporal lobe)?

A

Fibers from the right nasal hemiretina and the left temporal hemiretina (right temporal superior vision and left nasal superior vision) would be disrupted so the patient would not be able to see in the left upper nasal and right upper temporal
Contralateral superior quadrantansia

123
Q

What is contralateral superior quadrantanopsia?
A lesion to what area would cause this?
What is is more often referred to as?

A

When there is a lesion in the inferior optic radiation there will be a deficit in the superior contralateral quadrants.

Ex. Lesion to left inferior optic radiation would cause a deficit in upper left nasal and upper right temporal visual fields

Pie in the sky

124
Q

What visual deficits are associated with a lesion in the right superior optic radiation?
What region of the brain would this deficit be found in?

A

Contralateral inferior deficits so you would not be able to see the left inferior (right inferior nasal and left inferior temporal)

The parietal lobe

It is called contralateral inferior quadrantanopsia

125
Q

What is contralateral inferior quadrantanopsia?

What lesion is associated with it?

A

A lesion to the superior optic radiation would cause visual deficits in the contralateral inferior visual fields.

126
Q

What injury would you expect from a lesion in the primary visual cortex?

A

Loss of vision to the contralateral visual field but with MACULAR SPARING.

127
Q

What are the different locations the retina can send efferents?

A
  1. Lateral geniculate
  2. Superior colliculus
  3. Pretectal region
  4. Hypothalamus
128
Q

What is the major function the hypothalamus requires retinal input for?

What is the major function the pretectum needs retinal input for?

What is the major function the superior colliculus uses retinal input for?

A
  1. Regulating circadian rhythms
  2. Reflex control of pupils and lenses
  3. Orienting movement of head and eyes
129
Q
  1. What are the retinal afferents to the superior colliculus? (5)
  2. Are the retinal cells the same as those that go to the lateral geniculate?
  3. What tract do retinal fibers travel through to reach the superior colliculus?
  4. What are efferents from the superior colliculus? (5)
A
  1. -Ipsilateral temporal retina projections
    - contralateral nasal retina projections
    - primary visual cortex
    - somatosensory system
    - auditory system
  2. No they are a different subset of retinal ganglion cells
  3. Branchium of the superior colliculus
  4. -tectospinal tract to spinal cord
    - inferior colliculus
    - reticular formation
    - lateral geniculate
    - pulvinar nucleus
130
Q

What are afferents to the pretectal neurons?

Where do the pretectal neurons project to (where do their axons cross)?

A

Retinal ganglion axons traveling through the branchium to the superior colliculus that synapse before they reach it

They project to the edinger-Westphal nuclei bilaterally.
Their axons cross ventrally and dorsally to the cerebral aquaduct

Edinger-Westphal project to parasympathetic neurons in the ciliary ganglion to constrict the pupil and accommodate the lens

131
Q

Where do Edinger-Westphal nuclei project?

What do they do?

A

To the parasympathetic nuclei in the ciliary ganglion to constrict the pupil and accommodate the lens

132
Q

What retinal ganglion cells project to the hypothalamus?
What nucleus of the hypothalamus does it project to?
What does it do?

A

A subset that respond to direct photic stimulation (not dependent on photoreceptors)
Suprachiasmatic nucleus
It regulates circadian rhythms

133
Q

Where does the suprachiasmAtic nucleus project to?

A

The paraventricular nucleus of the hypothalamus which regulates ADH, oxytocin, autonomics in the brainstem and spinal cord.
Sympathetics in the lateral thoraco-lumbar spinal cord project to superior cervical ganglia, and pineal gland to make melatonin (sleep wake cycle)

Neuroscience Block 3 (20 decks)

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