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Neuro III > Vision > Flashcards

Vision Flashcards

1
Q

Describe the process of phototransduction in the outer segments of the rods

A

Photon absorbed by vitamin A on rhodopsin –> metarhodopsin –> activation of transducin (G protein) –> activation of cGMP PDE at cytoplasmic surface of disc membrane –> cGMP hydrolyzed to GMP –> closure of NSC channels –> hyperpolarization of rod membrane

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2
Q

What are the two types of ganglion cells in receptive fields?

A

ON-center ganglion cells and OFF-center ganglion cells

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3
Q

Describe ON-center ganglion cells

A

Excited by light shining in their centers, inhibited by light in their periphery

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4
Q

Describe OFF-center ganglion cells

A

Inhibited by light shining in their centers, excited by light in the periphery

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5
Q

Describe the sizes of the receptive fields in the fovea vs the periphery of the retina

A 
Fovea = receptive field as wide as a single cone
Periphery = large receptive field
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6
Q

What is the key determinant of receptive field type?

A

the type of glutamate receptor on bipolar cells. Excitatory –> OFF; Inhibitory –> ON

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7
Q

What type of synapses do bipolar cells make on ganglion cells?

A

Excitatory

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8
Q

what cells mediate the surround?

A

horizontal cells

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9
Q

What is the horizontal cell response to glutamate

A

inhibition of neighboring photoreceptors in the field center

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10
Q

What happens if light is shone on the PERIPHERY of an ON-center ganglion cell receptive field?

A

Hyperpolarized surround photoreceptors –> reduced glutamate secretion –> reduced activity of excitatory receptors on horizontals cells –> horizontal cell hyperpolarization –> decreased HC GABA secretion onto photoreceptors in field center –> decreased inhibition of photoreceptors –> increased glutamate release to bipolar cells –> inhibition (ON-center) of bipolar cells –> reduced excitatory input to ganglion cells –> reduced ganglion cell firing rate

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11
Q

Which synapses in the light-ganglion cell pathway are always excitatory?

A

surround photoreceptor + horizontal cell

Bipolar cell + ganglion cell

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12
Q

Which synapses in the light-ganglion cell pathway are always inhibitory?

A

horizontal cell + photoreceptor

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13
Q

Which synapse can be either excitatory or inhibitory?

A

Field center photoreceptor + bipolar cell

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14
Q

What effect does the light environment have on ganglion cells?

A

uniform illumination –> minimal firing

High contrast –> maximal firing

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15
Q

In which hypercolumn layer do LGN axons terminate?

A

layer 4

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16
Q

Describe ocular dominance columns

A

One for each eye. Ganglion cells at corresponding regions of retina from each eye –> LGN –> adjacent areas of cortex

17
Q

What are binocular cells?

A

cortical cells that receive input from both eyes

18
Q

If you view the hypercolumn from the cortical surface, what will you see?

A

Ocular dominance columns and binocular cells

19
Q

What hypercolumn structures handle information about color?

A

blobs

20
Q

Describe the visual field line orientations represented in hypercolumns

A

lie in different rays of pinwheels radiating from central blobs. Cells in vertical columns have the same line orientation sensitivity

21
Q

Describe the receptive field of simple cells

A

ON area that is a narrow line at a preferred orientation, flanked by OFF areas

22
Q

How are receptive fields of simple cells represented on V1 cortex?

A

Ganglion cells with OVERLAPPING ON-center receptive fields –> lined up –> converge on V1 cell (excitatory) –> V1 cell with receptive field equal to the sum of LGN receptive fields –> ON-center of a line with flanking OFF regions

23
Q

What stimuli do complex cells prefer?

A

lines or edges moving across the visual field

24
Q

How are complex cells created?

A

convergence of several simple cells with slightly offset positions

25
Q

How are color-opponent ganglion cells made?

A

Cones of different color preferences converge in the retina –> bipolar cells –> ganglion cells with receptive fields that are partial to particular colors

26
Q

Where in the eye are the highest concentration of cones

A

Fovea. All photoreceptors are cones

27
Q

What is the role of V1 in color processing?

A

V1 contains blobs, which are excited/inhibited by color. Blobs = not highly tuned to specific colors; unresponsive to shapes and white light

28
Q

What is the role of V4 in color processing?

A

color discrimination

29
Q

How is color discrimination achieved?

A

Cones respond to narrow bands of wavelength, Lateral inhibition –> further narrowing of wavelength response –> color discrimination

30
Q

What is the “sensitive period” in development of visual cortex?

A

Period of time when the connections to binocular cells in visual cortex can be altered by visual experience. Age 2-3

31
Q

What is the effect of monocular deprivation during the sensitive period?

A

loss of all cortical connections to the deprived eye.

32
Q

What is the effect of binocular deprivation during the sensitive period?

A

Normal V1 with disruption of higher-order visual cells. More nonresponsive cells, but most can be driven and are binocular

33
Q

What is the prevailing theory regarding cortical connections during the sensitive period?

A

Due to competition between inputs from the two eyes.
One eye receives input –> that eye drives all cortical cells
Neither/both eyes receive input –> binocularly driven cells

34
Q

What effect does strabismus have during the sensitive period?

A

One eye deviates –> two eyes looking at different parts of the visual world, receiving equal stimulation –> few binocular cells.
Nearly all cells driven by one eye or the other

35
Q

How is ocular dominance represented in hypercolumns?

A

Banded appearance from Layer 4 LGN axon terminals. Activity-dependent

Neuro III (17 decks)

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