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Neuro > Vision > Flashcards

Vision Flashcards

1
Q

What are the three kinds of cones and their wavelength?

A
  1. S-cones (short-wavelength) –> are sensitive to blue light and have a wavelength of around 425nm. Rhodopsin will be most activated.
  2. M-cones (medium-wavelength) –> are sensitive to green light. Absorption peak around 525nm.
  3. L-cones (long-wavelength) –> are sensitive to red light. Absorption peaks around 550nm.
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2
Q

What is magenta?

A

Magenta is not a single color it’s a lot of colors combined. Magenta is the whole spectrum and you take away green from the spectrum.

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3
Q

What is Trichromatic vision?

A

The ability of humans and some other animals to see different colors. 92% of males, and almost all females. Compare green and red photoreceptors.

8% of males are missing either M or L pigment.

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4
Q

What is tritanopia vision?

A

Tritanopia makes you unable to tell the difference between blue and yellow.

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5
Q

Edge detection:

A

Understand center-surround organization.

Retinal cells will have a receptor field (area of the world it looks at, based on which photoreceptors it connects to).

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6
Q

On-center/Off-center

A

Excited in the center, inhibited by light in the surround. Like light in the center and off in the surround.

Doesn’t like a light in the surround. Likes dark in the surround.

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7
Q

OFF-center/On-center

A

Opposite response

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8
Q

Determine the RGC Response to stimulus:

A
  1. Nothing –> get an action potential
  2. Bright spot in the center –> gets really excited and fires lots of fire potentials by retinal ganglia. GIVES THE BEST RESPONSE
  3. Bright spot covering the whole receptive field –> doesn’t like it much.
  4. Dark spot in the center, bright surround –> it really does not like it. It rebounds after it shuts off.

This is an ON-center/OFF-surround because of #2

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9
Q

Determine the RGC Response Properties

A
  1. Nothing
  2. Bright spot in the center –> it rebounds, fires more action potentials when you turn it off –> makes it dark again. Shuts up and doesn’t like it.
  3. Bright area covering the whole receptive field –> a little better but not much
  4. Dark spot in the center, bright surround –> very strong excited

This is an OFF-center/On-center because of #4

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10
Q

Receptive field

A

Ganglion cells are the first neurons in the retina that respond with action potentials.

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11
Q

Building on - and off-center circuits

A

All photoreceptors release glutamate. Will be releasing less glutamate in the light because photoreceptors hyperpolarize in the light, and less glutamate release.

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12
Q

What kind of receptors does OFF-center have?

A

They have excitatory cells AMPA/kainate receptors (+) and are excited by glutamate. If the photoreceptor receives light it will release less glutamate –> hyperpolarize. It is because it is normally excited in the dark it will be inhibited in the light.

OFF-center you get rid of excitation in the light.

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13
Q

What are the two types of bipolar cells?

A

The On-center bipolar cells will depolarize.
The OFF-center bipolar cells will hyperpolarize.

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14
Q

When a center cone is illuminated:

A

It will depolarize

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15
Q

What kind of receptors does On-center have?

A

They have metabotropic glutamate receptors (-) that are hyperpolarized by glutamate. In the dark, it’s going to get more glutamate gets more hyperpolarized.

Light comes on –> less glutamate –> depolarizes. Inhibition makes light excitatory bc you are reducing inhibition of the bipolar cell when the photoreceptors hyperpolarize.

When a center cone is illuminated it’s going to depolarize. Meaning the light source is producing light in the center of the beam.

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16
Q

How are bipolar cells connected to one another?

A

By horizontal cells

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17
Q

How are bipolar cells connected to one another?

A

By horizontal cells

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18
Q

If a center cone absorbs a photon what will happen?

A

It is going to be hyperpolarized and release less glutamate.

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19
Q

What is the bipolar cell: effect of glutamate?

A

On-center: it’s going to be inhibitory, when the light comes on in t1 there’s less inhibition and the on-center bipolar cells depolarize.

Off-center: excited by glutamate

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20
Q

What is the RGC response to bipolar?

A

On-center ganglion cell —> excited by light
Off-center ganglion cell —> inhibited by light

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21
Q

What do cones do in the dark?

A

They depolarize

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22
Q

What happens if you hyperpolarize the surrounding cone?

A

That will hyperpolarize the horizontal cell bc that cone to horizontal cell synapse signs preserving. If the cone goes down, the horizontal cell goes down.

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23
Q

What are the two types of bipolar cells?

A

The On-center bipolar cells will depolarize.
The OFF-center bipolar cells will hyperpolarize.

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24
Q

How excited will the retinal ganglia be if sitting in dim light?

A

Not very excited.

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25
Q

How excited will RGC be if you got part of the surround illuminated and part of the center illuminated?

A

Some excitation coming from the center, but the surround is reducing the excitation.

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26
Q

What happens when the edge has gone past the center so now the center is illuminated and part of the surround is illuminated?

A

You will get a strong excitation bc the center is very strong, and the surround is not inhibiting as much bc it’s not a completely illuminating surround.

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27
Q

Photoreceptors in the Human Retina

A

looking at something straight ahead will be at 0 degrees –> land on the fovea (highest density of photoreceptors)

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28
Q

Should you look directly at objects in low light?

A

no bc cones have poor sensitivity.

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29
Q

cGMP

A

This molecule opens up specialized dark current Na+ channels. This is made by guanylate cyclase.

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30
Q

How does cGMP respond to light?

A

The amount of cGMP present decreases with the advent of light, causing dark current sodium channels to close. Photoreceptor cells then hyperpolarize in the presence of light.

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31
Q

What do cones do in the dark?

A

They depolarize

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32
Q

Glutamate from photoreceptors excites horizontal cells

A

when a cone is hyperpolarized by the light the horizontal cells is hyperpolarized by light

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33
Q

Lateral inhibition:

A

Glutamate from photoreceptors excites horizontal cells –> when a cone is hyperpolarized by the light the horizontal cell is hyperpolarized by light.

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34
Q

Center cone

A

change the output of the center cone depending on what the surrounding cone is seeing. Horizontal cells will change the output. The output of photoreceptors in the center will depend on input from the surround

35
Q

If you put light on the surrounding cone does what to the center cone/bipolar?

A

It will hyperpolarize the surrounding cone, it will hyperpolarize the horizontal cell, and it will depolarize the center cone bc there will be less inhibition.

36
Q

What is sign preserving synapse?

A

When the photoreceptor cell depolarizes, the bipolar cell also depolarizes. Accordingly, this synapse is sign-conserving: when light falls on the rod or cone, the bipolar cell hyperpolarizes (because the photoreceptor hyperpolarizes).

37
Q

T1 center (illuminate)

A

Light hyperpolarizes the center cone, and will get less glutamate from the center cone. Horizontal cells on either side are going to be slightly hyperpolarized.
On-center bipolar and RGC will be excited, not illuminating the surroundings right now the horizontal cells don’t play a big role.

38
Q

T2 will illuminate the surround

A

Donut of light, hyperpolarize horizontal cells, less GABA on the terminal of the center cone. Will be depolarizing the center cone and more glutamate release, and inhibit bipolar and RGC.

39
Q

What does lateral inhibition do?

A

Through the center cone, if you illuminate the surround, you will hyperpolarize your horizontal cells –> reducing the amount of GABA in the center cone. Less GABA on the center cone will depolarize and more glutamate.

If this was an off-center bipolar cell (depolarize) it would be like this bc there would be more glutamate available at T2.

40
Q

Where do retinal ganglion cells go

A

They come out of the eye and go to multiple places.

41
Q

Hypothalamus:

A

regulation of circadian rhythms

42
Q

Pretectum:

A

pupillary reflex

43
Q

Superior colliculus (optic tetum):

A

orientation movements

44
Q

Coming out of eye

A

The optic nerve carries retinal ganglion axons.
When they get to the brain, they crossover –> optic chiasm
The next nerve is the optic tract –> carries axons from the optic chiasm to the thalamus.
From the thalamus to the visual cortex is the optic radiation

45
Q

The retina is a map of visual space

A

We are taking a map of the world and turning it into neuroactivity and sending it to the brain.

46
Q

Binocular vision

A

The optic nerve contains axons coming from a single eye
Left eye (orange) orange part of the retina is looking at the right visual field (across). That orange part of the retina is projecting to the same side (left optic tract). In that same eye, you have purple neurons (nasal part of the retina) project across the optic chiasm to the other side.

The left side of the world goes to the right brain, and the right side of the world goes to the right brain.
-left temporal and right nasal in retina –> looking at the orange side of the world (right side), and our axons from the left temporal and right nasal will come together in the optic tract and bring that information into the left visual cortex.

The purple side of the world is falling on the left nasal and right temporal, the right temporal stays on the right eye and the left nasal crosses over and follows the right optic tract.

47
Q

Nasal RGB axons cross to the other side at optic chiasm

A

Temporal axons stay on the same side, optic tract contains axons from both eyes that receive contralateral information

48
Q

Onward to the cortex

A
  • On the left optic tract (red axon from the temporal left side) (blue axon coming from the nasal right side)
  • axons project to the lateral geniculate nucleus of the thalamus
    -the inputs from the two sides are segregated, the red and blue axons synapse in different places in the LGN
  • Inputs from two eyes are kept seperate
49
Q

Optic tract

A

The left optic tract is responsible for the right visual field, and the right optic tract corresponds to the left visual field

50
Q

LGN neurons to primary visual cortex (V1)

A
  • “striate cortex”
    -the first place where two eyes are compared
    -map of retina maintained throughout, where the temporal left eye (red) projects will be appropriate for where it’s looking in space.
    -map of world on the primary visual cortex (V1)
51
Q

What happens if you cut optic chiasm? Which axons travel in the optic chiasm? Cut B

A

All of the nasal axons, everyone who is looking at the right lateral and left lateral. You lose the lateral world bc nasal axons (the ones that cross) look at this. Light coming from the lateral side, left nasal retina is looking way off to the left – lose that bc you have lost those nasal neurons (cut their axons)

52
Q

If you have a lesion in the system, you will lose a certain part of the visual field. Whats going to happen in the visual world

A

What will you be missing if you cut the right optic nerve? Cut A. will be missing everything that came out of the right eye (right lateral world) if you lose one eye you can still see the entire visual field from the left side bc you have your temporal left retina. You can still have a good bit of the right eye because you have that left temporal side functioning. Can see much of the world.

53
Q

Scotoma:

A

small loss

54
Q

Anopsia

A

large deficit

55
Q

What if you C –> optic tract

A

The optic tract carries axons that all look at the same place in space. The right optic tract looks at the opposite side –> left world which means you are going to lose the left side of the world.

56
Q

What if you cut the optic radiation? Make a cut at D what will you see?

A

A little loss of upper left side

57
Q

What happens if you cut E –>

A

Lose the entire left side except for the fovea

58
Q

Striate Cortex is stripy (looking outside of it)

A

Primary visual cortex. The heavily myelinated stripe in the middle of the cortex is distinct –> called striate cortex bc it looks stripey.

59
Q

Like somatic sensory system, there is a map of the world in the visual cortex

A

The rear of the brain is the center of the field, the periphery is more forward.

60
Q

Map of visual space

A

Retina has a fovea in the middle of it, purple –> fovea, color coding shows where the different parts of the retina map on the visual cortex.

61
Q

Would you expect the area devoted to fovea to be large or small?

A

It’s much bigger –> overrepresented. The fovea is where you are focusing most of your attention.

62
Q

What do neurons in the visual cortex respond to?

A

Hubel and Wiesel recorded from neurons in a cat’s visual cortices
looked for stimuli that made the cells fire

63
Q

Organization of V1

A

The cortex is a sheet (cortex is about 2mm thick and has multiple layers)
- Left side nissl stain –> which stains nuclei in cell bodies
-input is coming in from 4a and 4c from the thalamus
Input (blue) and outputs (red and green)
- outputs: ascending (cortex): 2/3 & 4B, descending (superior colliculus, thalamus): 5 & 6

64
Q

Responses of V1 Neurons in layers

A

-Use a metal electrode that can record spikes from single units (neurons)
-poke electrode straight into the cortex, as it goes deeper and deeper it will go to different parts of the cortex.

65
Q

Cortical receptive fields organization

A

-move electrode vertically through the cortex, neurons respond to similar features
- location of receptive field in space, much change? No

66
Q

Orientation selectivity? How does it change

A

Spike change compared to orientation, if you do vertical series of recordings (all in the same column) they will like the same thing
-move the electrode tangentially, as you move you will be moving across to a different part of the cortex that will have a different receptive field.
Orientation tuning: how does it change? It likes horizontal bars, in C it likes vertical bars, when you keep moving orientation will shift again until you get horizontal.

67
Q

Fibers from which structure(s) cross the midline prior to synapsing in the cerebellum?

A

Pontine nuclei

68
Q

The axon terminals of neurons projecting to the cerebellum from pontine nuclei, the spinal cord, and vestibular are called

A

mossy fibers

69
Q

As a result of cerebellar long-term depression

A

inhibition of neurons in deep cerebellar nuclei by Purkinje neurons is reduced

70
Q

During sensitization of the gill withdrawal reflex in Aplysia, serotonin (5-HT) release is caused by

A

a noxious stimulus to the tail

71
Q

Facilitation of the gill-siphon withdrawal reflex in Aplysia

A
  • requires serotonin
  • involves block of a K channel
  • all of these
  • is heterosynaptic
72
Q

According to Hebb’s postulate, a weak synapse on a postsynaptic neuron will become stronger

A

if the synapse is repeatedly activated at the same time the postsynaptic neuron fires

73
Q

All of the following statements about late long-term potentiation (ILTP) are true except

A
74
Q

In order to disrupt a memory of that has already formed through fear conditioning, anisomycin must be administered

A

at the time the memory is recalled

75
Q

In classical conditioning, the subject will respond to the unconditioned stimulus

A

always

76
Q

which of the following is not affected by blocking protein synthesis?

A

massed training

77
Q

Feedback information about motor errors is transmitted to the cerebellar cortex via

A

climbing fibers from neurons in the inferior olive

78
Q

Long-term potentiation can activate “silent” synapses by

A

causing the addition of AMPA-type glutamate receptors

79
Q

If the active zones at a given synapse normally have a very high probability of releasing a vesicle in response to a single action potential, then the response to a second action potential is likely

A

depressed

80
Q

Which of the following is an example of heterosynaptic plasticity

A

sensitization of the Aplysia gill withdrawal reflex

81
Q

Short-term synaptic depression can be caused by

A
82
Q

Classical conditioning is a form of

A

implicit memory

83
Q

An important distinction between classical and operant conditioning is that operant conditioning requires

A

the subject to take an action

84
Q

Compared to wild-type flies, dunce flies

A

do not learn to associate odor with foot shock

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