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Optometry Class OP4102 > Receptive fields and visual pathways > Flashcards

Receptive fields and visual pathways Flashcards

1
Q

how are on centre bipolar cells stimulated? How are they inhibited?

A

-stimulated by a decrease in glutamate from cones and rods and so are depolarised by increased luminance.
-inhibited by an increase in luminance from cones and rods and so are hyperpolarised by a decrease in luminance

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2
Q

what could you look at to trigger a strong response from on centre bipolar cells?

A

light images on dark backrounds

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3
Q

how are off centre bipolar cells stimulated and how are they inhibited?

A

-stimulated by an increase in glutamate from cones so are depolarised by reduction in luminance
-inhibited by decrease in glutamate from cones so are hyperpolarised by increase in luminance

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4
Q

what could you look at to trigger a strong response from off centre bipolar cells?

A

dark images on light backgrounds

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5
Q

What are the two types of cells in the fovea?

A

parasol cells and midgit cells

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6
Q

what are the 5 functions of horizontal cells?

A

-carry info horizontally across the retina in the outer plexiform layer
-feed information between bipolar cells
-feedback info to photoreceptors
-communicate with other horizontal cells through gap junctions
-receive feedback from inner plexiform layer
-shape receptive fields of bipolar cells
-send feedback to photoreceptors, modulating photoreceptor signal under different light levels

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7
Q

What are amacrine cells?

A

interneurons that carry info laterally through the inner plexiform layer and synapse with bipolars, amacrines and ganglion cells

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8
Q

what do amacrine cells do?

A

help sharpen up receptive fields of ganglion cells like horizontal cells do for bipolar cells

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9
Q

what is the definition of the receptive field of a cell that transmits visual signals

A

the area of the retina over which a light stimulus can change the activity of that cell

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10
Q

what is the dendritic field of a ganglion cell?

A

the physical area of the dendritic arbour

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11
Q

what is the receptive field of a ganglion cell

A

the area of photoreceptors that will ultimately contribute to the response of the ganglion cells

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12
Q

what is the significance of horizontal cells in terms of receptive field?

A

they add an opponent signal to the receptive field and introduce centre-surround antagonism

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13
Q

how does the configuration of the receptive field come about and what is it shaped as ?

A
  1. horizontal and amacrine cells contribute to the formation of receptive field configuration
  2. RF centres have a positive response to it’s preferred stimulus
  3. RF surrounds have a negative response to the same stimulus
  4. the positive and negative responses combine to give the Mexican hat configuration
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14
Q

what cell recieves centre surround organisation of bipolar cell RFs?

A

ganglion cells

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15
Q

what cells modify the RF of ganglion cells?

A

amacrine cells

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16
Q

how are on centre ganglion cells affected by the RF?

A

they respond strongly to light on the centre of the RF and dark on surround

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17
Q

how are off centre ganglion cells affected by the RF?

A

they respond strongly to dark ion centre of RF and light on surround

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18
Q

give three consequences of the centre-surround organisation

A

-centre-surround organisation manifests as spatial antagonism
-the visual system responds strongly to luminance boundaries and less strongly to even, unchanging areas of luminance
-ganglion cells are spatially tuned to spots of different sizes

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19
Q

how do ganglion cells show spatial tuning

A

they are size specific as in they respond most strongly to a stimulus of a specific size so any larger or smaller and the response is reduced

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20
Q

what are achromatic pathways?

A

these compare brightness of an image across the retina

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21
Q

what cones are responsible for achromatic pathway through the retina

A

L-cones and M-cones

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22
Q

what cones are responsible for colour pathways across the retina?

A

L, M and S cones

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23
Q

what are chromatic pathways

A

compare wavelength of light across the retina

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24
Q

how is convergence associated with receptive fields give examples for the rod system and cone system

A

convergence determines the size of receptive fields
-the rod system has lots of convergence at 120:1 so sensitive = large receptive field but poor resolution
-the cone system has little convergence at 6:1 so less sensitive = small receptive field but better resolution

25
Q

what do parallel pathways do and what are the 3 major channels they are carried in?

A

they provide distinct and separate processing and transmission through the visual pathway
channels are
-parvocellular
-magnocellular
-koniocellular

26
Q

which channel of parallel pathways are contributed by
rods?
cones?

A

rods mainly contribute to magnocellular pathway and cones to both magnocellular and parvocellular

27
Q

Where is the lateral geniculate nucleus located?

A

in the thalamus in the forebrain

28
Q

what type are the 6 layers of the lateral geniculate nucleus (LGN)? what is between the layers?

A

-layers 1 and 2 are magnocellular layers
-layers 3,4,5 and 6 are parvocellular layers

koniocellular cells between the layers

29
Q

which layers of the LGN are for the ipsilateral eye and which are for the contralateral eye?

A

-2,3 and 5 are ipsilateral
-1,4,6 are contralateral

30
Q

what is the lateral geniculate nucleus? what does it do? what does it relay info to and receive feedback from?

A

-it is the first extra-retinal synapse in the visual pathway, has centre surround receptive fields and has the retinotopic map in each layer
-it slows firing rate of signals to the brain to prevent over stimulation of the visual cortex
-relays info to higher cortical centres and receives feedback from visual cortex and other cortical and subcortical areas

31
Q

where in the brain is the striate cortex located?

A

in the occipital lobe

32
Q

what is the primary visual cortex called?

A

brodmann area 17

33
Q

what are 3 types of cortical neurones and what does the way they respond to stimuli mean they are?

A

-simple cortical cells
-complex cortical cells
-end-stopped cells
they are orientation specific as they respond best to bar-like stimuli

34
Q

What are complex cortical cells sensitive to?

A

-orientation of the stimulus
-direction of movement
-speed of movement

35
Q

when my complex cortical cells not be senstivve to a stimulus?

A

if is is stationary

36
Q

what stimulus do complex cortical cells respond best to?

A

a correctly orientated bar of light moving across a receptive field

37
Q

what so end stopped cells respond best to?

A

moving corners

38
Q

what are end stopped cells sensitive to?

A

movement
length

39
Q

how are end stopped cells sensitive to length of stimulus?

A

as they have inhibitory regions at the end of the receptive field

40
Q

give the receptive field characteristics of simple cortical cells

A

they are excitatory and inhibitory areas arranged side by side and respond best to bars of particular orientation

41
Q

what are the receptive field characteristics of RGCs

A

they have a centre surround receptive field that responds best to spots of certain size while also responding to other stimuli

42
Q

give three functional properties cells within a column have in common

A

-location
-orientation
-ocular dominance

43
Q

how do cells within a location column and in neighbouring columns compare

A

location column cells have receptive fields from the same part of the retina and neighbouring columns cells have receptive fields from neighbouring parts of the retina

44
Q

compare the foveal representation in the cortex with that of the periphery and give 2 reasons why

A

in cortex its magnified compared to the periphery because:
-there is a greater density of ganglion cells in the central retina
-each ganglion cell in the central retina has greater representation in the cortex than each ganglion cell from the periphery

45
Q

give the effects of monocular deprivation

A

-optic radiations from the non-deprived eye = greater axonal arbor complexity
-optic radiations from the deprived eye = reduced axonal arbor complexity

46
Q

what is the hypercolumn?

A

the 1mm block of cortex which is a processing module serving a particular area of the retina

47
Q

what does each hypercolumn contain?

A

-blobs which are chromatic information from red-green and blue-yellow opponent pathways
-interblobs which are cells specific to orientation and achromatic contrast

48
Q

what is the magnocellular pathway from retina to visual cortex?

A

low-contrast, flicker, movement, spatial location of objects, achromartic, poor spatial resolution

49
Q

what is the parvocellular pathway from retina - visual cortex?

A

chromatic, high contrast, high spatial resolution

50
Q

what are the 11 visual areas of the brain?

A

-frontol lobes
-parietal lobes
-occipital lobes
-V5
-V3A
-V2
-V1
-V4
-LGN
-temporal lobe

51
Q

in the brain, what is area V2

A

receives bulk of the input from the striate cortex

52
Q

how can eye disease symptoms change the hill of vision in visual fields?

A

-only being able to see dimmer light = the hill becoming flatter
-patchy vision = local dips in the surface

53
Q

how does static perimetry work? why?

A

the stimuli change from not seeing to seeing to find the threshold. the different stimuli in different locations are to find the height of the hill of vision at that particular location in the field

54
Q

what does the threshold in visual field depend on?

A

-the size of the stimulus
-duration of the stimulus

55
Q

why is small bright light likely to have the same visibility as larger dim light?

A

because two or more stimuli within one receptive field get added together to give a single response as in summation

56
Q

what is ricco’s law?

A

if you double the stimulus area, the amount of light required to reach threshold is halved and this is applied within the critical area hence complete spatial summation. beyond critical area, summation is partial

57
Q

how does threshold in a visual field depend on size?

A

as visibility is determined by total amount of light falling within a receptive field so a critical number of quanta falling on a receptive field is needed for the stimulus to be seen.

58
Q

what does bloch’s law describe and how?

A

temporal summation as if we double stimulus duration, we only need to halve the luminance to bring it to threshold this is in the critical duration where complete temporal summation occurs

59
Q

give reasons why spatial and temporal summation are important for perimetry

A

-both spatial and temporal summation are altered in glaucoma
-spatial summation only is altered in AMD
-stimuli with a fixed luminance varying in area appear to have better performance characteristics in identifying glaucomatous damage than the current clinical standard
-the finding of altered temporal summation in glaucoma suggests that perimetry could be improved my reducing the duration of the stimulus and that the current duration actually masks an important functional biomarker for the condition

Optometry Class OP4102 (19 decks)

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