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Visual Science > Retinal projections: parallel processing pathways (to the thalamus & midbrain) > Flashcards

Retinal projections: parallel processing pathways (to the thalamus & midbrain) Flashcards

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1
Q

which two major classes of retinal ganglion cells have concentric surround receptive fields that turns them into luminance contrast detectors

A

midget/parvo
&
magno/parasol

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2
Q

where do midget & parasol retinal ganglion axons travel down and end up

A

travel down the optic pathway

end up at LGN of thalamus

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3
Q

what is the third cell in addition to midget and parasol, that end up at the LGN

A

konio-cellular systems

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4
Q

what is the divisions of labour/specialisations for visual perception

A

functional specialisations that divide different aspects of our visual perception processes.

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5
Q

what does the divisions of labour/specialisations for visual perception begin with

A

the three types of retinal ganglion cells found in the retina

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6
Q

list the three main sub-classes of retinal ganglion cell

A
  • midget/parvo
  • parasol/magno
  • small bi-stratified/konio
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7
Q

what are the properties of the midget/parvo sub-class of RGC

A

detailed form processing/high acuity & colour processing (red/green) distinguish green from yellow

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8
Q

what are the properties of the parasol/magno sub-class of RGC

A

global (not fine) form/low acuity vision & motion (flicker, good a detecting change)

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9
Q

what are the properties of the small bi-stratified/konio sub-class of RGC

A

colour (blue/yellow)

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10
Q

what do RGC’s that are not involved in perception send their axons to in not to the LGN

A

different non-geniculate nuclei outside the thalamus

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11
Q

what are the further divisions of labour/specialisations mediating visual reflexes

A
  • circadian rhythms
  • pupillary light responses
  • eye movements
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12
Q

how much % does the midget/parvocellular sub-class of RGC represent of all ganglion cells

A

majority - 80%

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13
Q

what are the anatomical features/structure of the midget/parvocellular sub-class of RGC

A
  • small cell bodies
  • short dendrites
  • small diameter axons
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14
Q

where are the midget/parvocellular sub-class of RGC concentrated

A

concentrated in the central retina

fewer peripherally

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15
Q

which of the LGN layers do the midget/parvocellular sub-class of RGC project

A

to the parvocellular layers 3-6

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16
Q

how much % does the parasol/magnocellular sub-class of RGC represent of all ganglion cells

A

10%

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17
Q

what are the anatomical features/structure of the parasol/magnocellular sub-class of RGC

A
  • large cell bodies

- wide dendritic trees

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18
Q

where are the parasol/magnocellular sub-class of RGC concentrated

A

even distribution across central to peripheral retina

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19
Q

which of the LGN layers do the parasol/magnocellular sub-class of RGC project

A

to the magnocellular layers 1 & 2

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20
Q

how much % does the small bi-stratified or koniocellular sub-class of RGC represent of all ganglion cells

A

5%

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21
Q

what are the anatomical features/structure of the small bi-stratified or koniocellular sub-class of RGC

A
  • small cell bodies
  • wide dendritic trees
  • very thin axons
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22
Q

where are the small bi-stratified or koniocellular sub-class of RGC concentrated

A

concentrated in the central retina

very few peripherally

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23
Q

which of the LGN areas do the small bi-stratified or koniocellular sub-class of RGC project

A

the inter-laminar zones of the LGN

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24
Q

which RGC has wider dendrites than parasol magno cells

A

small bi-stratified RGCs

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25
Q

why is the name given to small bi-stratified RGCs

A

have two strata which go into the inner plexiform layer to receive input from bipolar cells

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26
Q

which sort of shape do the dendrites of parasol magno RGCs resemble

A

come out like an umbrella in a 3D form

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27
Q

where do the dendrites of the parasol magno RGCs go to and why

A

go to the inner plexiform layer where it receives synaptic input from bipolar cells

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28
Q

what are the parasol magno cell RGCs RFs larger than

A

midget cells

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29
Q

what do the parasol/magno RGC axons have around them and why

A

myelin for faster conduction

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30
Q

where are konio cells scattered in the LGN

A

scattered/dotted about in the inter laminar zones between the major (P&M) cell layers 1-6

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31
Q

what are the white bands between the cells in the LGN

A

white matter which are axons of the RGC trying to get neurons they want to make connections with and are also axons of LGN that want to send information further up the pathway to the primary visual cortex

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32
Q

what do the white band of the axons of the RGC separate

A

the grey matter neurone cell bodies from each other

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33
Q

what do the darker dots on the LGN show

A

the bigger cells/cell bodies of the LGN

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34
Q

what type of RFs do midget parvocellular RGC sub-classes have

A

small RFs

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35
Q

what type of responses do the RFs of the midget parvocellular RGC sub-classes have

A

sustained/long responses

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36
Q

what type of centre-surrounds do midget parvocellular RGC sub-classes have within their RFs

A

ON/OFF luminance and red/green contrasts

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37
Q

what type of luminance: spatial frequencies do midget parvocellular RGC sub-classes have

A

high spatial frequencies (high acuity and fine detail, interested in contrast)

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38
Q

due to the high spatial frequencies that midget parvocellular RGC sub-classes have, what type of contrast sensitivity do they have

A

low contrast sensitivity

need high contrast to keep them going as they are not sensitive to lower contrast

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39
Q

what type of acuity is midget parvocellular RGC sub-classes associated with

A

high acuity (detailed form)

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40
Q

as well as high acuity and detailed form, what else is midget parvocellular RGC sub-classes associated with

A

colour

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41
Q

what type of RFs do parasol magno cellular sub-classes have

A

larger RFs

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42
Q

what type of responses do parasol magno cellular sub-classes have

A

transient (brief) responses

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43
Q

what type of centre-surrounds do parasol magno cellular sub-classes have

A

ON/OFF centre surrounds luminance only (achromatic)

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44
Q

what type of luminance: spatial frequencies do parasol magno cellular sub-classes have

A

low spatial frequencies

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45
Q

due to the low spatial frequencies that parasol magno cellular sub-classes have, what type of contrast sensitivity do they have

A

high contrast sensitivity (stimulate to low contrasts)

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46
Q

swell as high contrast sensitivity, what else do parasol magno cellular sub-classes have

A

also high temporal frequencies (flicker)

47
Q

what type of acuity is parasol magno cellular sub-classes associated with

A

low acuity (global form)

48
Q

as well as low acuity and global form what else is parasol magno cellular sub-classes associated with

A

motion

49
Q

what type of RFs do small bi-stratified or koniocellular sub-classes have

A

small RFs

50
Q

what type of responses do small bi-stratified or koniocellular sub-classes have

A

sustained responses

51
Q

what do small bi-stratified or koniocellular sub-classes not have

A

centre-surround or luminance

52
Q

what are small bi-stratified or koniocellular sub-classes only associated with

A

blue-yellow contrasts only

53
Q

what are removed except at the block borders of global forms

A

filtered images with fine detail (high spatial frequencies) as seen by the lower acuity parasol or mango-cellular system

54
Q

what can global forms (low acuity vision) still be used to

A

roughly identify things

55
Q

what do both midget & parasol RGCs possess

A

ON-OFF or OFF-ON centre-surround concentric type RF organisations & generate responses that emphasise luminance (brightness) differences at contrast borders in the visual image

56
Q

what different contributions do midget & parasol RGCs make

A

to the retinal contrast sensitivity function (CSF)

57
Q

what is the normal human visual system most sensitive to in the contrast sensitivity function

A

3-8 cycle per degree (cod)

58
Q

describe the properties of the pallie robson chart

A

a contrast chart with:

  • high contrast at top and low contrast at bottom
  • but all letters have the same spatial frequency (1cpd = low spatial frequency)
59
Q

what is 1 cod equivalent to

A

in one degree of visual field there is one black bar and one white bar

60
Q

how many black and white bars are in one degree of visual field

A

30

61
Q

where does the low contrast and highest spatial frequency cut off

A

where no one can tell the contrast around 30 cpd

62
Q

wha va’s is 30cpd equivalent to

A

6/6 & 6/4.8 = 40cpd

63
Q

what type of contrast is a low spatial frequency

A

high contrast

64
Q

at which point of spatial frequency in cpd is the highest sensitivity

A

5 cpd

65
Q

which va’s is 5 cpd equivalent to

A

9/60 or logmar 0.7

66
Q

what is the preferred spatial frequency of both RGC types magno and parvo

A

match the size of their ON & OFF sub-regions of their RFs

67
Q

which RGCs can the ON-centre OFF-surround RF belong to

A

both midget and parasol RGCs

68
Q

when will a RGC like a particular stimulus and fire a large response

A

e.g. when the ON-centre is filled by the light bar and OFF-surrounds covered by dark bars i.e. the spatial phase of the contrast borders maximally excites both the light ON-centre & light OFF-surround zones of the cells RF

69
Q

because centre-surround RF sizes influence spatial frequency selectivity, what effect is there with midget cells RFs

A
  • smaller receptive field

- centres & surrounds are more responsive to higher spatial frequencies

70
Q

because centre-surround RF sizes influence spatial frequency selectivity, what effect is there with parasol cells RFs

A
  • larger receptive field

- centres & surrounds are more responsive to lower spatial frequencies

71
Q

so what is the difference if RF sizes responsible for

A

the tuning of midget & parasol RGCs

72
Q

which RGC likes lower spatial frequencies/high contrast sensitivity

A

parasol/magno cells

73
Q

what is the whole contrast sensitivity function made of

A

separate channels with smaller curves makes up the whole anatomy

74
Q

what are the individual channels which make up the whole contrast sensitivity function a response property of

A

individual neurons of ganglion cells in the retina

75
Q

what are the midget and parasol RGCs sensitive to within the contrast sensitivity function

A

the peak/middle range = 3-8 cpd where both RGCs contribute

76
Q

what do midget and parasol ganglion cells decrease in with retinal eccentricity

A

density

77
Q

what do midget and parasol ganglion cells increase in with retinal eccentricity

A

size

78
Q

how much of visual angle in degrees is 1mm equivalent to

A

2.2 degrees

79
Q

how much of visual angle in degrees is 10mm equivalent to

A

22 degrees

80
Q

at 2.2 degrees (foveal 1 degree angle) of visual angle, how much larger does this value make the dendritic fields of midget & parasol RGCs

A

20x and 10x larger respectively

81
Q

as a result of dendritic sizes of the midget and parasol RGCs increasing with eccentricity, what else increases as a consequence

A

RF sizes

82
Q

what does the increasing RF sizes with eccentricity contribute to

A

the reducing acuity (high spatial frequency cut off) of the CSF in peripheral 22 degrees verses foveal 1 degrees

83
Q

which visual angle out of 22 and 1 degrees does not have good acuity

A

22 degrees

84
Q

what type of cone inputs do midget cells receive

A

selective cone inputs

85
Q

what are the midget cells responses influenced by, as they receive selective cone inputs

A

influenced by the wavelengths of the luminance contrast borders

86
Q

what type of cone inputs do parasol ganglion cells receive

A

mixed cone inputs

87
Q

what are the parasol ganglion cells responses influenced by, as they receive mixed cone inputs

A

ONLY influenced by the luminance differences

88
Q

what cones do the bipolar cells which supply to the parasol RGCs get

A

mixture of both red & green cones
so both are responsible for its centre and surround
and the mixture of red and green cones so will like the red and green stripes in its RF as the ON response is mediated by both cones so can respond to either

89
Q

if a midget cell RF = red-ON green-OFF what type of response is given

A

maximal response to red ON/dark with minimal or no response to green ON/dark gratings and some response to white ON/dark as theres some red in white light

90
Q

what does a parasol RF respond to

A

just ON-OFF

so doesn’t care if ON is white red or green

91
Q

which RGC have sustained responses

A

midget cells

92
Q

which RGC have transient/detect flicker responses

A

parasol cells

93
Q

what is the peak temporal frequency of a midget/parvo RGC

A

10Hz

94
Q

what is the cut off temporal frequency of a midget/parvo RGC

A

20Hz

95
Q

what is the peak temporal frequency of a magno/parasol RGC

A

10Hz

96
Q

what is the cut off temporal frequency of a magno/parasol RGC

A

50Hz

97
Q

what is the significance of a magno/parasol RGC having a cut off temporal frequency of 50Hz

A
  • high temporal contrast = can detect flicker (50 flashes a second)
  • better for detecting image motion
98
Q

does does critical flicker fusion frequency mean

A

highest flicker that the visual system can follow (=50Hz)

99
Q

which RGCs are concentrated at the retina

A

midget

100
Q

which RGCs have large, heavily myelinated axons

A

parasol

101
Q

which RGCs are particularly sensitive to blue/SW light

A

bi-stratified

102
Q

which RGC gives transient responses to light stimulations

A

magno/parasol

103
Q

what are the RFs of parvo, magno or konio LGN cells similar to

A

those of the (P, M or K) retinal ganglions that supply their specific synaptic inputs

104
Q

what is the difference between the RFs of parvo, magno or konio LGN cells compared to the P, M or K retinal ganglions that supply their synaptic inputs and why

A

they are slightly larger than the ganglion cells that supply them input
due to convergence from several ganglion cells of one type & even less responsive to diffuse light (due to stronger ‘lateral’ inhibition in the LGN itself)

105
Q

The LGN acts mainly to organise the synaptic inputs into…

A
  • function-specific layers (including the interlaminar zone)
    before sending the information on, still in parallel, to the primary visual (v1) cortex in the occipital lobe
    required for visual perception

i.e. one of the main functions of the LGN is not to change the receptive field properties of the inputs, but is to do this

106
Q

what do the parallel image processing in the primary visual pathway send information of different LGN layers into

A

parallel pathways up to different neurons in the visual cortex

107
Q

where do parallel pathways beginning continue through to

A

begin in the retina and continue into the LGN which then continued from LGN and end up into the primary visual cortex

108
Q

what happens to the other RGC sub-classes which are not involved in visual perception who’s axons don’t project to the LGN

A
  1. either stop off earlier (above the optic chiasm) in the hypothalamus
    or
  2. go down the tract and continue past the LGN (go into the special fibre pathway called the superior brachium) and ends up in separate nuclei of the midbrain, behind the thalamic
109
Q

what do the non-perceptual parallel processing pathways include

A
  • (1) projections from specialised photosensitive (melanopsin-containing) cells to the
    suprachiasmatic nucleus of the hypothalamus
    &
  • 3 parallel pathways to the upper midbrain
    from other photosensitive-type ganglion cells to:
    > olivary pretectal nucleus (OPT): for the pupillary light reflex (constriction)
    & from other members of the small bi-stratified sub-classes to:
    > superior colliculus (SC): for fast eye movements to novel stimuli
    > accessory optic nuclei (AON): for optokinetic reflex during head motion
110
Q

what is melanopsin

A

visual pigment which transduces light from a wide region of space during a long time & only interested in day time & night time as they are radiance detectors where the illuminance of day & night regulates our biological clock, which regulates our circadian rhythm

111
Q

what do the ganglion cell axons which end up in the hypothalamus contain

A

melanopsin

112
Q

what does melanopsin contain

A

contain ganglion cell dendrites which span over wide regions of the retina containing melanopsin

113
Q

what does melanopsin not do

A

dont transduce light from local regions of space

Visual Science (14 decks)

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