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ANAT 321 > The Visual System > Flashcards

The Visual System Flashcards

1
Q

The Andromeda Galaxy

A

Can see w naked eye
Can’t tell if it is an ellipse or circle tilted on it’s side
This is problem w visual system

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2
Q

Sensation is an abstraction, not a replication of the real world

A
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3
Q

The eye is like a camera

A

Focused light is projected on retina
Optic nerve creates optic disc which is blind spot

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4
Q

Horizontal cells and Amacrine cells

A

Connect photoreceptors together
Connect ganglion cells

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5
Q

What is closest to the retina?

A

Retina-
Photoreceptors
Horizontal cells
Bipolar cells
Amacrine cells
Retinal Ganglion cells
-Front of eye

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6
Q

How many layers in retina?

A

10 layers

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7
Q

Fovea

A

High-acuity center of visual field
Cells are pushed out of the way
Photoreceptors have direct access to light in the fovea
It is intended

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8
Q

17 distinct

A
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9
Q

Do all neurons fire action potentials? Give an example of what doesnt

A

NO
Rods and cones do not

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10
Q

Are cones or rods concentrated in the fovea?

A

Cones, no rods

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11
Q

Nasal side

A

Rods concentration, no cones
Optic disc

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12
Q

Temporal side

A

Rods, no cones

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13
Q

Light sensitivity

A

Rods are more sensitive to light but have low acuity
Cones are less sensitive to light but have high acuity
Examples: seeing a faint star, will be brighter if you look slightly to the side of it because rods will be perceiving it

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14
Q

In dark

A

cGMP flowing around cells, high concentration
It binds to ion channel that is permeable to sodium, sodium flows in
In the dark the photoreceptor is depolarized

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15
Q

When light hits photreceptor?

A

cGMP phosphodiesterase activated and reduces concentration of cGMP so Na channels close

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16
Q

Photoreceptors are _____ in the dark

A

depolarized

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17
Q

Photoreceptors are _____ in the light

A

hyperpolarized

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18
Q

How is rhodopsin activated?

A

Light causes conformational change

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19
Q

Transducin (G-protein)

A

Activated by Rhodopsin

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20
Q

cGMP Phosphodiesterase

A

Breaks down cGMP which results in sodium channels closing

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21
Q

Do any of the 5 cell types in the retina fire action potentials

A

Retinal Ganglion

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22
Q

Intensity of light is transformed…

A

Into the frequency of APs in retinal ganglion cells

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23
Q

Horizontal cells

A

Inhibit NT release from cone in the dark

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24
Q

If light shines on central cones

A

AP increases

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25
Q

If on horizontal cells

A

It is inhibited

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26
Q

In dark

A

Calcium flows in
Cone releases Glutamate

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27
Q

In light

A

Calcium stops
Cone does not release NT

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28
Q

How does glutamate affect the bipolar cell

A

Glutamate actually hyperpolarizes the bipolar cell which is weird bc we usually think of glutamate as excitatory

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29
Q

Does bipolar cell fire AP?

A

No

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30
Q

Bipolar cell synapses on RGC and…

A

Excitatory glutamate at the synapse

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31
Q

Is RGC firing AP in the dark?

A

No

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32
Q

Why is glutamate inhibitory b/w cone and bipolar cell?

A

Bc receptors are metabotropic

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33
Q

In the dark the cone…

A

Releases a lot of glutamate

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34
Q

In bright light

A

Amount of glutamate is dramatically reduced

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35
Q

Intermediate light

A

Cone will only be somewhat hyperpolarized so it will release sort of less glutamate

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36
Q

Amount of glutamate being released is a continuous function of…

A

How much light the cone absorbs

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37
Q

The change in membrane potential is going to be a continuous function of…

A

How much light the cone absorbs
How much glutamate the cone releases

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38
Q

The amount of glutamate that it releases is going to be a continuous function of…

A

How much light the cone absorbs

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39
Q

If light is dim…

A

Cone hyperpolarizes a little bit

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40
Q

If cone hyperpolarizes a little bit…

A

Bipolar cell depolarizes a bit

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41
Q

If bipolar cell depolarizes a little bit

A

The bipolar cell will release some glutamate onto the ganglion cell and ganglion cell will increase it’s firing

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42
Q

Explain the idea of inhibition by horizontal cells

A

Imagine 3 photoreceptors.
One of them is connected to a bipolar cell which is connected to a ganglion cell
When the photoreceptors surrounding it are hit by light this causes the horizontal cell to INHIBIT NT release from the center photoreceptor connected to this RGC

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43
Q

What determines if RGC will be on center or off-center

A

Bipolar cell

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44
Q

Cones in fovea…

A

Each cone is connected to a glutamate (inhibitory) - ON bipolar cell
AND
A glutamate (excitatory) - OFF bipolar cell

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45
Q

What happens to receptive fields as you move away from the fovea?

A

They become larger
Multiple PR’s contribute to the center and to the surround
Lotta convergence
This why they are more sensitive to light but less precise

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46
Q

There are more then a dozen distinct types of RGC’s. How many?

A

17

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47
Q

Each type of retinal ganglion cell tiles the retina

A

Jus like somatosensory system (corpuscles)

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48
Q

3 best characterized channels from the retina. 3 kinds of RGC’s that we know the most about

A

Midget ganglion cells
Parasol ganglion cells
Bistratified ganglion cells

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49
Q

% of RGC’s that are midget ganglion cells

A

70%

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50
Q

% of RGC’s that are parasol ganglion cells

A

10%

51
Q

% of RGC’s that are bistratified ganglion cells

A

8%

52
Q

Small cone and wavelength

A

Blue cone - 445nm

53
Q

Medium cone and wavelength

A

Green - 535nm

54
Q

Large cone and wavelength

A

Red - 575nm

55
Q

Midget cells

A

Can see how much green vs red
Very concentrated in the fovea
They are the first step(neurons) of the p-pathway
Center of their receptive fields is made of one cone, very high resolution
Midget cells are high precision but not good at detecting rapid changes

56
Q

How many types of midget ganglion cells?

A

4

57
Q

Where do midget cells synapse?

A

Parvocellular layer in the LGN (p-pathway)

58
Q

For green center and red surround what cones are where

A

Green cone in center, red cones surrounding it

59
Q

How are midget cells also edge detectors?

A

White light makes everything activate

60
Q

Parasol cells

A

m-pathway
Have larger receptive fields
Only recognize illumination
Really good at detecting rapid changes
Both center and surround or mixed up w red and green cones
These can’t tell diff b/w red and greed they are just activated anyways

61
Q

Bistratified cells

A

k-pathway
Convey relative amount of blue vs yellow
Project to koniocellular layers of LGN

62
Q

Yellow is…

A

Mix of green and red light

63
Q

Parasol

A

Luminance
L+M

64
Q

Midget

A

L vs M
Red/green

65
Q

Bistratified

A

S vs (L+M)
Blue/Yellow

66
Q

Which are more complex? The receptive fields of RGCs or PR’s?

A

As a result of the convergence of multiple PR’s individual RGC’s the receptive fields of RGC’s are more complex then those of photoreceptors

67
Q

Visual pathway

A

Optic nerve–> optic chiasm –> optic tracts –> LGN

68
Q

Midget and parasol ganglion cells project to how many layers in LGN?

A

6 distinct layers
1 is most medial

69
Q

Each layer has

A

Full retinotopic map

70
Q

Lateral projections…

A

Ipsilateral
Layers 2,3,5

71
Q

Nasal projections

A

Contralateral
Layers 1,4,6

72
Q

Do LGN neurons relay inputs from RGCs to V1 faithfully without significant change in the receptive fields?

A

YES

73
Q

Projections that go on lower pathway from LGN to V1 represent…

A

Top half of visual space

74
Q

Projections that go on higher pathway from LGN to V1 represent…

A

Bottom half of visual space

75
Q

How does LGN output project to V1?

A

Optic radiation

76
Q

Lot more projections going to LGN from cortex or vice-versa?

A

Lot more from V1 to LGN

77
Q

Superior colliculus

A

Involved in saccadic eye movements

78
Q

Pretectum

A

Pupillary reflexes

79
Q

Superchiasmatic nucleus of the hypothalamus

A

Modulates circadian rhythms

80
Q

Distribution of projections from RGC’s?

A

90%
- LGN
10% split b/w:
- superior colliculus
- pretectum
- superchiasmatic nucleus

81
Q

What separates occipital lobe from rest of brain?

A

Parieto-Occipital sulcus

82
Q

V1 neurons respond best to bars of light?

A

Bars of light at a particular orientation

83
Q

Torsten Wiesl and David Hubel

A

Learned how brain neurons encode visual stimuli

84
Q

V1 Location

A

Brodmann’s area 17
Around the Calcarine sulcus

85
Q

Left primary visual cortex represents…

A

Right side of visual space

86
Q

Ventral part of primary cortex reps..

A

top half of visual space

87
Q

Top half of V1 reps…

A

Bottom half of visual space just like optic radiation

88
Q

Inputs from thalamus terminate in…

A

Layer 4

89
Q

LGN neurons project mainly to layer…

A

4c

90
Q

K-pathway

A

From thalamus to superficial layer (2,3)
Directly to BLOB
BLOB projects to the VENTRAL - WHAT pathway

91
Q

P-pathway

A

From LGN to layer 4Cbeta
Projects to Blob and inter-blob then to VENTRAL - WHAT pathway

92
Q

M-pathway

A

From LGN to 4Calpha to 4B
To blob and inter-blob to the Ventral-WHAT pathway
4B projects to Dorsal, Where pathway

92
Q

Where does 4B from M-pathway project?

A

Dorsal, Where pathway

92
Q

The elongated receptive fields of simple cells are built from convergent input from…

A

many layer 4 cells with roughly circular receptive fields

92
Q

Blob

A

Involved in color vision

92
Q

Cortical columns

A

Orientation-selective columns
Arranged in a complex pattern of swirls
A cycle around a swirl contains neurons responding to the full range of orientations for a particular location in space

92
Q

Inter-blob

A

Shape of objections
Mixing of P-pathway and M-pathway

92
Q

Hypercolumn

A

Column containing all possible orientations of a region of visual space

93
Q

Simple cells

A

On center, off-surround

94
Q

Complex cells

A

Don’t have inhibition, just need an edge anywhere in their receptive field

95
Q

Some neurons have a motion preference

A

Subset of neurons, bars of light have to move in a particular direction

96
Q

Some V1 neurons are sensitive to bar length

A
97
Q

Blobs found in…

A

Layer 2 and 3

98
Q

Blobs are interspersed within the orientation columns

A

They respond to color
Interblob are orientation

99
Q

Ocular dominance columns

A

Superimposed on the orientation columns and blobs are columns corresponding to alternating input from the ipsilateral and contralateral eyes.
These are called ocular dominance columns.

100
Q

Dorsal stream

A

Where, goes along parietal lobe
Location and movement

101
Q

Ventral stream

A

Encodes form and color
What stream

102
Q

Area MT

A

In the dorsal stream is involved in detection of motion

103
Q

If dots move at random, 50% correlation and 100% correlated
What is threshold

A

What is threshold of detection for people to know that dots are moving in particular direction
Usually 10% threshold

104
Q

If lesion in MT neurons

A

Deficit in detecting global motion, understanding which direction things are moving

105
Q

Aperture problem

A

V1 receptive fields are small, may give misleading info on direction of movements
Can be deceived about direction of motion.

106
Q

Dorsal stream multimodal sensory pathways from…

A

Parietal cortex to premotor cortex

107
Q

How is aperture problem fixed?

A

Neurons in area MT integrate input from neurons with smaller receptive fields so they can detect the overall direction of movement of an object

108
Q

People who have lesions to these particular color areas can not imagine color even if they had color vision before
Idea about memory, how are erasing this piece of memory?

A
109
Q

Fusiform face area

A

Faces

110
Q

Prosopagnosia

A

Loss of ability to recognize familiar faces

111
Q

feedback connections may be involved in visual attention and..

A

top down anticipator mechanisms that enable us to differentiate an object from the background

112
Q

Predictive processing

A

Prediction error signals are fed forward to update predictive model at the next level in the hierarchy
Expectation vs input = error
Error goes up to correct error

113
Q

Blindsight

A

Blind man can avoid obstacles
V1 on right side of brain so he can’t see things on left side
Superior colliculus is connected to parietal and frontal lobes. even though V1 gets no info, there is this extra stream that allows blindsight to happen
Involved in detecting motion and controlling eye movements

114
Q

Another unconscious pathway goes from thalamus (LGN and pulvinar) to the amygdala. what is it involved in?

A

Rapid, unconscious emotional responses to visual stimuli. Like seeing a bear pass you at night.

115
Q

Projections to prefrontal cortex are involved in…

A

Visual working memory

116
Q

The binding problem

A

How is visual stuff unified? How are the diff components of vision (form, color, location, motion) spread out over disparate regions of cortex, bound together to form unified, coherent percept

117
Q
A

ANAT 321 (17 decks)

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