L3 - overview of the visual system Flashcards

1
Q

3 types of stimuli for visual system

A

food
predator
mate

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2
Q

what is negative feedforward

A

when GABA neurons activate neurons downstream

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3
Q

what is meant by - the optic nerve is an information bottleneck

A

it cannot process everything that the retina acquires rejects a lot of information

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4
Q

functions of the retina

A

image acquisition

filters information and adapts

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5
Q

what is the function of the lateral geniculate nucleus (LGN)

A

preprocesses the visual information - deep in brain so difficult to research

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6
Q

function of visual cortex

A

place of main processing of information

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7
Q

2 main visual pathways in the cortex

A

ventral stream and dorsal stream

the two influence each other

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8
Q

ventral stream

A

used to process object identity (what), terminates in the inferior temporal complex

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9
Q

dorsal stream

A

used to process information about the location, speed, direction of the object (where). terminates in the posterior parietal complex

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10
Q

function of the pupil

A

regulates amount of light that falls on the retina

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11
Q

function of the lens

A

focuses the image on the fovea (part of the retina)

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12
Q

what is the fovea

A

part of the retina with the highest visual acuity

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13
Q

what does light travel through

A

transparent muller cells within the retina

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14
Q

layout pf the retina

A

3 layers of neurons and 2 layers of synapses
feedforward neurons - photoreceptors, bipolar cells and ganglion cells
feedback neurons - horizontal cells and amacrine cells

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15
Q

pathway through the retina

A

info starts in photoreceptors
goes to bipolar cells
goes to ganglion cells
goes through optic nerve to the brain

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16
Q

what are the two levels of synapses in the brain

A

inner and outer plexiform layers

17
Q

what is the outer plexiform layer

A

contains synapses between photoreceptors, bipolar cells and horizontal cells

18
Q

what is the inner plexiform layer

A

contains synapses between bipolar cells, amacrine cells and horizontal cells

19
Q

what is active and dim light and what is active at bright light

A

rods active at dim light

cones active at bright light

20
Q

where does phototransduction occur

A

in the outer segment of rods and cones

photoreceptors respond to light flashes by hyper polarisation

21
Q

phototransduction cascade

A

1) shine light on photoreceptor, opsin change their conformation
2) activates the G-protein coupled receptors
3) G alpha subunit dissociates which activates phosphodiesterase
4) phosphodiesterase causes a drop in the concentration of cyclic GMP
5) decrease in cGMP causes a closing of the change;s
6) closing of the channels causes hyper polarisation of the membrane

22
Q

what is the phototransduction cascade sensed by

A

hyperpolarisation causes a decrease in glutamate release
glutamate concentration sensed by bipolar and horizontal cells
less glutamate = less. activation of bipolar and horizontal cells

23
Q

what are the two types of bipolar cells

A

ON cells - depolarise when light intensity increases

OFF cells - hyper polarise when light intensity increases

24
Q

what does less glutamate lead to regarding OFF cells

A

less glutamate leads to less depolarisation of OFF cells therefore they hyperpolarse

25
what receptors do OFF cells express
ionotropic glutamate receptors (excitatory) coupled to G-proteins - leads to less closing of channels
26
what receptors do ON cells express
metabotropic glutamate receptors (inhibitory) - AMPA
27
what is a receptive field
an area in the retina which when illuminated activates a visual neuron
28
what is center-surround organisation
illumination of the centre and the surround leads to responses in opposite polarities
29
what cells have centre surround organisation of their receptive field
bipolar and ganglion cells
30
what occurs during stimulation of the centre of the receptive field of an ON cell
get a depolarisation and if stimulate away from the centre get a hyper polarisation
31
stimulation of an OFF cell with spot and annulus
``` spot = hyperpolarisation annulus = depolarisation ```
32
bipolar cells receive input from what 2 cells
photoreceptors activate directly and indirectly direct - located in centre of receptive field, leads to hyperpolarisation of OFF cell indirect - stimulation of surrounding photoreceptors causes inhibition of horizontal cell - no longer inhibits bipolar cell leads to depolarisation
33
what are located in the same subliminal in the IPL
axons of ON bipolar cells and dendrites of ON ganglion and amacrine cells
34
large number of dendritic trees =
more connections so may be responsible for higher sensitivity vision
35
larger size of dendritic tree =
larger receptive field, not as good for high acquit vision. more suited for change within a large area
36
properties of parvocellular ganglion cells
``` small field sustained reponse slow conduction velocity low sensitive function to detect form/colour ```
37
properties of magnocellular ganglion cells
``` large field transient response fast conduction velocity high sensitivity function - motion detection ```