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Neural circuits > Lecture 4 - visual system > Flashcards

Lecture 4 - visual system Flashcards

1
Q

what does each layer of neurons contain?

A

some neurons with positive projections and negative feedback of downstream level back by inhibitory neurons and negative feedforward

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2
Q

main function of the retina

A

image acquisition and send to the brain

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3
Q

lateral geniculate nucleus (LGN)

A

another pre-processing sensor and processing visual information before the cortex

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4
Q

where does the main processing of information happen?

A

in the visual cortex

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5
Q

ventral stream pathway

A
  1. ventral stream is V1,V2 and V4 and involved in object identity located in inferior temporal lobe
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6
Q

dorsal stream pathway

A

dorsal stream is localizing object for speed and direction and is responsible for spatial location

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7
Q

what are the 5 layers of the retina

A

consists of 3 layers of neurons and 2 layers of synpases

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8
Q

signalling in the retina

A

photoreceptors signal with bipolar cells which signal with ganglion cells

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9
Q

what activates the ganglion cells?

A

glutamate expressed in the bipolar cells

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10
Q

what inhibits the ganglion cells?

A

GABA expressed by Amacrine cells which send information back and forward

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11
Q

what are the feedforward neurons?

A

photoreceptors, bipolar cells and ganglion cells

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12
Q

what are the feedback neurons

A

horizontal cells and amacrine cells

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13
Q

what does the outer plexiform layer consist of?

A

consists of synapses between photoreceptors, bipolar cells and horizontal cells

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14
Q

what does the inner plexiform layer consist of?

A

consists of synapses between bipolar cells, amacrine cells and ganglion cells

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15
Q

what does bipolar cells and horizontal cells receive their input from? (laminar organisation)

A

photoreceptors in outer plexiform layer

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16
Q

what does ganglion cells and amacrine cells receive their input from?

A

bipolar cells (and ganglion cells from amacrine cells) in the inner plexiform layer

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17
Q

rods vs cones

A

rods are active at dim light and cones are active at bright light

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18
Q

where does phototransduction happen?

A

in the outer segment (disks)

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19
Q

what do photoreceptors do?

A

respond to bright flashes by hypolarisation, a decrease in membrane potential. they allow efficient release of glutamate

20
Q

what is the key molecule in phototransduction?

A

cGMP which activates specific ion channels on the membrane

21
Q

what happens in darkness? (phototransduction)

A

there is lots of cGMP which actviates a channel and when it opens the membrane depolarises and membrane potential increases

22
Q

what happens when cGMP is converted to GMP? (phototransuction)

A

channel closes and membrane potential decreases which involves rhodopsin

23
Q

what does light cause in photoreceptors?

A

causes a conformational change in rhodopsin and triggers a G protein cascade which leads to a decrease in amount of cGMP and closes the channel

24
Q

what makes photoreceptor synapses special?

A

have special structures where they can sustain a consistent release of glutamate

25
Q

what decrease glutamate release?

A

light activation

26
Q

ON bipolar cells vs OFF bipolar cells

A

ON bipolar cells depolarise when activated by light and OFF bipolar cells hyperpolarise

27
Q

mechanism of ON cell activation

A
  • express mGluR instead of AMPAR to signal a cascade
  • G protein not the same as photoreceptor cascade
  • removal of cGMP is not required for ion channel closure
  • TRMP1 expressed in ON cells
28
Q

what is required for light and glutamate response in ON cells

A

Nyctalopin and protrohylcan

29
Q

what are located in the same sublaminae in IPL?

A

axons of ON bipolar cells and dendrites of ON ganglion cells and amacrine cells

30
Q

what is the receptive field?

A

area in the retina which when illuminated activates a visual neuron

31
Q

center-surround organisation

A

center-surround of receptive field means the center and the surrounding area leads to responses in opposite polarities

32
Q

which visual cells have center-surround of receptive field

A

bipolar and ganglion cells

33
Q

annulus

A

this is the outer part of the receptive field

34
Q

inputs at the center vs inputs at the outer part

A

inputs at the center signal directly with bipolar cells and ones on the outer part indirectly bind with bipolar cells using horizontal cells

35
Q

stimulating the center of receptive field (bipolar cell)

A

stimulating the centre of receptive field, only stimulates the center

36
Q

stimulating outer part of receptive field (bipolar cells)

A

if surrounding area is stimulated, it stimulates the outer photoreceptors to cause a reverse effect and depolarisation

37
Q

illuminating the whole receptive field in ganglion cells

A

this does not activate ganglion cells - designed to respond to differences in illumination within receptive field

38
Q

stimulation of OFF center

A

they stop spiking and when the light decreases, they start spiking again

39
Q

stimulation of ON center

A

when stimulating the ON center, there is increase in spiking rate and when light decreases they stop spiking

40
Q

what is center-surroun organisation the result of?

A

results from inhibitory feedback from amacrine cells

41
Q

what are the two main classes of ganglion cells?

A

parvocellular (80%) and magnocellular (10%)

42
Q

parvocellular vs magnocellular

A

parvocellular has smaller dendritic trees and can distinguish the different colours of light

43
Q

parvocellular vs magnocellular (processing information)

A

parvocellular process information about shape and colour. magnocellular process information about motion

44
Q

cones received by parvocellular cells

A

can receive red cones in the center and green cones in the surrounding part

45
Q

morphology of ganglion cells dendritic trees

A
  • differ in size of dendritic tree where smaller trees process more detailed information
  • can be asymmetric
46
Q

where does adaptation originate

A

in the retina and downstream

47
Q

adaptation vs sensitisation

A

adaptation results in a decrease in spiking where sensitisation results in an increased spiking. adaptation for visual illusions

Neural circuits (11 decks)

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