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NEURO 0010 > visual > Flashcards

visual Flashcards

1
Q

where vs. what areas regarding vision?

A

where
- dorsal visual cortex areas

what
- ventral visual cortex areas

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2
Q

what is the cornea?

A

glassy transparent surface of the eye
-> it is continuous with the sclera
(white of the eye/wall of the eyeball)

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3
Q

what is the pupil?

A

the opening that lets light into the eye surrounded by pigmented iris
- iris = what gives eye its color

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4
Q

what is the lens?

A

located behind the iris and suspended by ligaments called zonule fibers (connected ciliary muscles)

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5
Q

how does the lens function in regarding to liquid in eye?

A

the lens divide liquid in eye into aqueous humor and vitreous

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6
Q

where is aqueous humor located?

A

behind cornea/in fornt of the lens

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7
Q

where is vitreous humor located

A

behind lens, keeps eye ball spherical

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8
Q

what is the retina?

A

area in the back of the eye that contains photo receptors

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9
Q

what is the optic disk?

A

where the retinal vessels originate and where optic nerve fibers exit
- there are no photoreceptors
- blind spot

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10
Q

what is the macula?
what does it contain?

A
  • yellowish region responsible for central vision
  • relatively lacks large blood vessels
  • contains the fovea
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11
Q

what is the fovea?
what are the distinctions of the fovea?

A

def: center of the retina

distinctions
nasal
- retinal surface closer to the nose/medial relative to the fovea

temporal
- retinal surface closer to temple/lateral relative to fovea

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12
Q

what is the specialization of the fovea?
where does this specialization come from?

A

specialized for high acuity vision

due to
- highest density of cone photoreceptors
- no blood vessels obscuring retinal surface
- inner retinal layers pushed aside

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13
Q

what is refraction in the eye?
- what are the index’s of refractions present in the eye

A

cornea
-> aqueous vitrus and humor
-> lens

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14
Q

what is the amount that light bends in the eye due to?

A

amount of bending is proportional to the index of refraction
- higher index = greater bending

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15
Q

what is unique about the cornea and eye refraction?

A

cornea contributes most to light refraction because it is the first part of the eye that the light hits

sharpest change in index refraction

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16
Q

what is the purpose of the lens in regards to refraction?

A

the purpose of the lens is to accommodate via modulation of the shape of the lens

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17
Q

what happens to light when the lens is fattened?

A

the light bends more

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18
Q

what are zonule fibers and ciliary muscles?

A

zonule
- the tiny thread-like fibers that hold the eye’s lens firmly in place

ciliary
- changes the shape of the lens when your eyes focus on a near object

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19
Q

lens and fibers: far object?

A

less bending -> flattens
- because object is already parallel

zonule = tight
ciliary = relaxed

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20
Q

lens and fibers: close object?

A

more bending-> fattens
- because object is not as parralell

zonule = loose
ciliary = tight

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21
Q

what are the 2 refractive errors?

A

myopia
- cant see far objects which require less refraction
myopia cause
- too much refraction
- eye is too long horizontally
solution
- concave lens

hyperopia
- cant see near objects which require less refraction
hyperopia cause
- too little refraction
- eye is too short horizontally
solution
- convex lens

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22
Q

what are the 5 classes of retinal neurons? (bottom to top)

A

1) photo receptors (rods, cones)
2) bi-ploar cells
3) horizontal cells
4) amacrine cells
5) ganglion cells

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23
Q

how many retinal layers are there? what are the types?

A

5
- 3 nuclear layers (cell bodies)
- 2 plexiform layers (synapses)
plexi = network of neurons

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24
Q

how do horizontal cells function?

A
  • they get input from photo receptors
  • influence photoreceptors and bipolar cells
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25
Q

how do amacrine cells function?

A
  • get input from bipolar cells
  • influence bipolar and ganglion cells
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26
Q

what does the light hit first?

A

the ganglion cells

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27
Q

what do photoreceptors do? why are they unique?

A

they transduce light into a change in membrane potential

they are the only light-sensitive cells in the retina

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28
Q

how do non photoreceptor retinal cells fire in response to light?

A

via direct or indirect synaptic connections

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29
Q

what is a unique property of disks that help with them absorb light?

A

light-sensitive photoreceptors help absorb light to trigger Vm changes

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30
Q

what is melanopsin, where is it located?

A

ipRGCs contain melanopsin, large RFs allow humans to synchronize behaviour to changes in light (circadian rhythm)

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31
Q

why are retinal ganglion cells unique?

A

1) because they are the only retinal cells to fire action potentials
2) they send axons out of the optic nerve

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32
Q

where do ganglion cells project to?

A

Thalamus - LGN
(lateral geniculate nucleus)

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33
Q

rods. vs cones
- appearance
- light sensitivity
- mid-light
- concentrated in
- types
- color reception

A
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34
Q

what is rhodopsin?

A

rod pigment and functions like receptor for signal cascade

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35
Q

when is the acuity of rods best vs. cones?

A

rods
- best in periphery in scotopic conditions
cones
- best in fovea in photopic conditions

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36
Q

what is visual acuity?

A

they eyes ability to distinguish between 2 points (spatial sensitivity of the eye)

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37
Q

what are the electrical currents within the photoreceptors?

A
  • outward K+
  • inward Na+
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38
Q

what is the inward current of the photoreceptors called, what is the current gated by?

A

Na+ current is called “dark current”, because it is not based on light stimulation

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39
Q

how does light activate photopigment?

A
  • photopigment is located in discs of the outer segments
  • light changes the confirmation (shape) of the photopigment
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40
Q

what is the Vm of photoreceptors in dark conditions?

A

Vm = -30mV

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41
Q

what are the 2 reasons why the photoreceptors have fundamentally different electrical activity?

A

1) they have more Na+ leak channels
2) Photoreceptors hyper-polarize to light

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42
Q

what keeps Na+ channels open?

A

secondary messenger cGMP keep Na+ channels open

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43
Q

what is opsin?
what is retinal?
what is bleaching, what does bleaching cause?

A

opsin
- receptor protein (has 7 transmembrane regions like G protein-couples receptors)

retinal
- is pre-bound against opsin

bleaching
- light changes conformation of retinal -> it activates opsin
- activates G-protein transducin
- transducin activates PDE
- reduces levels of cGMP
- Na+ channels close, hyper polarization

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44
Q

what are different photoreceptors hyperpolarized by?

A

different wavelengths of light

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45
Q

what is the color we perceive based on?

A

it is based on the relative activation of R, G and B cones

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46
Q

is color a physical property?

A

no, color is a function of the mind
- different species presumably experience color differently

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47
Q

where are each RGB pigment located?

A

Red and green = X chromosome
Blue = chromosome 7

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48
Q

how do our eyes deal with sustained changes in light?

A

adaptation

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49
Q

what is adaptation?

A

changes in visual sensitivity when there is a sustained change in light level

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50
Q

what are the 2 kinds of adaptation?

A

1) dark adaptation
(adapting to darkness)
2) light adaptation
(adapting to light)

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51
Q

what are the mechanisms for adaptation?

A

1) pupil constriction or dilation
2) switch between rods and cones
3) Ca++ feedback in photoreceptors

52
Q

how do pupils adapt to light?

A

high intensity of light
-> constriction of pupils

low intensity of light
-> dilation of pupils

details
constriction
- increases depth of focus

reflex is consensual
- shining light on one eye while other is covered will cause both to constrict

53
Q

what is the range that you can see when adapting?

A

the more light, the photoreceptors will hyperpolarize
- cones can only change over a 10^3 range of light intensity

54
Q

how is cGMP synthesized?

A

cGMP is synthesized by guanylyl cyclase from GTP

55
Q

how does each photoreceptor adapt? (group or independent)

A
  • each photoreceptor adapts independently
56
Q

what is an afterimage?

A

the image seen after adaptation

57
Q

rod and cone adaptations
low light vs. high light

A

low light
- rods become higher input for ganglion cells

high light
- cones become higher input for ganglion cells

58
Q

what do the 3 different types of opsin in the cones represent?

A

RGB
red=long
green=medium
blue=short

59
Q

what does right temporal see?
what does right nasal see?

A

right temporal
- left central

right nasal
- right peripheral
- right central

60
Q

what does left temporal see?
what does left nasal see?

A

left temporal
- right central field

left nasal
- left peripheral
- left central

61
Q

where do nasal portions decussate?

A

at optic chiasm

62
Q

what do the optic tracts carry?

A

information from the contralateral visual field

63
Q

what is the fovea specialized for?

A

high acuity vision
- fovea’s have the highest cone density
- no overlaying blood vessels
- inner retinal layers pushed aside

64
Q

describe rod and cone distribution?

A

92 million rods
5 million cones
1.5 million axons leave the eye -> much signal processing in the eye

65
Q

what is the result of the distribution of cones and rods in the eye?

A

blind spot

color vision
- best in fovea
- poor in periphery
- none at night

acuity
- best in fovea with photopic light
- best in periphery with scotopic light
(fins a star on a moonless night)

66
Q

what is the receptive field of a neuron?

A

the field of stimulus to which a cell responds

67
Q

what is the best or optimal stimuli for a cell?

A

the one that causes the maximal response

68
Q

photoreceptor receptive field?

A

spot of light on retina

69
Q

bipolar cell, ganglion cell, thalamus
receptive field?

A

have center/surround antagonistic RFs

ON-center/OFF-surround
or
OFF-center/ON-surround

70
Q

V1 - receptive field?

A

Bar of light with a particular orientation

71
Q

dorsal secondary visual area - receptive field?

A

spots of light moving in particular direction -> motion processing

72
Q

ventral secondary visual area - receptive field?

A

biologically significant objects -> form/color processing
- hand or a particular person

73
Q

what do photoreceptors release when depolarized?
what happens when there is more light?

A

glutamate

more light = greater hyperpolarization
-> less glutamate is released

74
Q

what are the two types of bipolar cells?

A

On and Off

75
Q

what is the purpose of lateral inhibition?

A

to enhance visual contrast

76
Q

what are the cells that fire action potentials in the visual system?

A

retinal ganglion cells

77
Q

what are the different types of retinal ganglion cells?

A

magno, parvo, nonM-nonP

78
Q

describe magno RGCs

A
  • 5% of RGCs
  • Large RFs
  • Color insensitive
  • Transient burst of APs
79
Q

describe parvo cells

A
  • 90% of RGCs
  • Small RFs
  • Color sensitive
  • Sustained discharge of APs as long as stimulus is present
80
Q

describe nonM-nonP RGCs

A
  • 5% of RGCs
  • small RFs
  • most are color sensitive
  • Poorly charachterized
81
Q

what is the LNG?

A

a thalamic nucleus that relays information from the retina to the primary visual cortex.

82
Q

where is the LGN located?
why are there 2?

A
  • It is located in the thalamus
  • There are 2 because the thalamus is a bilateral structure
83
Q

What is the distribution of input in the LGN?

A

20% = retina
80% = V1

84
Q

how many layers are in the LGN?

A

6

85
Q

what layers of the LGN receive signals from the ipsilateral eye?

A

2, 3, 5

86
Q

what layers of the LGN receive input from the contralateral eye?

A

1, 4, 6

87
Q

what layers of the LGN receive input from the different types of RGCs?

A

1 & 2 = Magno
3, 4, 5 and 6 = Parvo
Koniocellular = nonM-nonP input

88
Q

LGN functions?

A
  • thalamic relay between optic tract and V1
  • dreams in burst mode
  • visual attention
89
Q

what is the dorsal stream of the LGN?

A

Magno LGN -> 4C alpha-> 4B -> Occipital/Parietal

90
Q

what is the ventral stream of the LGN?

A

Parvo LGN -> 4C beta -> 2/3 -> Occipital/Temporal

91
Q

what is the occipital and temporal cortex related to?

A

identification and recognition

92
Q

what is the occipital and parietal cortex related to?

A

motor, visual motion, visual control of action

93
Q

what are retinotopic projections an example of?

A

topography/topographic maps

94
Q

what is the significance of layer 4C?

A

1) inputs from the L and R eye remain segregated
2) Layer 4C is monocular, the last time in the visual pathway where input from the two eyes is separated
3) the receptive field properties are center/surround antagonistic RF

95
Q

describe how V1 layers outside of 4C function?

what do the V1 layers contain, and produce?

A

they are binocular but are still dominated by one eye depending on their proximity to left eye input in layer 4C or right eye input in layer 4C

contain
- cortical modules

produce
- ocular dominance columns

96
Q

in what direction do ocular dominance columns run?

A

perpendicular to V1 layers

97
Q

describe orientation selectivity?

A

certain orientation gives highest response and form orientation columns

98
Q

what is orientation selectivity used for?

A

form perception

99
Q

direction selectivity?

A
  • makes up a subset of neurons that are orientation selective
  • response based on orientation and direction of movement
  • response is also grade
100
Q

what is direction selectivity used for?

A

motion perception

101
Q

what are the characteristics of a simple cell?

A

1) orientation selective
2) distinct on/off areas
3) center-surround RF inputs

102
Q

what are the characteristics of a complex cell?

A

1) orientation selective
2) on/off areas overlap
3) presumably constructed from the summation inputs from multiple simple cells preferring the same orientation

103
Q

parvo and konio factors?

A
  • ventral and cortical areas
  • form and color
  • “what”
104
Q

magno factors?

A
  • dorsal cortical areas
  • motion
  • “where”
105
Q

5 factors of the V1 cortical modules?

A

1) each cortical module is necessary and sufficient to analyze a particular point
2) removal -> blind spot in visual area
3) 2 pairs od ocular dominance columns
4) 2 complete samplings of all 180 of possible orientation columns
5) also contain 16 cytochrome oxidase blobs

106
Q

what is achromatopsia?

A

cortical color blindness

107
Q

akinetopsia

A

motion blindness

108
Q

what is the purpose of the dorsal stream?

A

for analysis of visual motion and visual control of action

“where”

109
Q

describe area V5/MT?

A
  • nearly all cells are direction selective
  • unlike V1 has direction columns
  • large RFs, responsive to stimulus motion direction
110
Q

describe area MST?

A
  • cells selective for types of motion
  • proposed purposes: navigation, directing eye movements, motion perception
111
Q

what could damage in the dorsal stream cause?

A

akinetopsia

112
Q

what is the purpose of the ventral stream?

what could damage to this area cause?

A

for perception of visual world and recognition of objects “what”

  • prosopagnosia, inability to recognize faces
113
Q

describe area V4?
what could damage to this area cause?

A
  • very large RFs with color and orientation selectivity
  • achromatopsia
114
Q

what is area IT?

A

farthest extent of visual processing
- faces, objects with biological significance
- large RFs
- may be important for recognition and visual memory

115
Q

what is the area associated with face recognition?

A

fusiform face area

116
Q

what 2 areas are in the dorsal stream?

A

area V5/MT
area MST

117
Q

what 3 areas are in the ventral stream?

A

area v4
area IT
fusiform face area

118
Q

in what layer of the V1 does LGN feedback occur?

A

layer 6 of V1

119
Q

what layer of the V1 controls eye movements

A

layer 5

120
Q

what happens during spiking mode?

A

LGN firing follows ganglion cell input

121
Q

what happens during intrinsic burst mode?
what role does it play?

A

LGN cut off from sensory input
- dreams
- visual attention

122
Q

what is the function of orientation selectivity?

A
  • form orientation columns
  • used for edge detection
    and form perception
123
Q

what is the function of direction selectivity?

A
  • used for motion perception
124
Q

what do cortical modules contain that are important?

A

cytochrome oxidase blobs

125
Q

what are the cytochrome oxidase blobs used for?

A

color perception/processing

126
Q

what does the v1 contain? what are the functions of the v1?

A

contains
4C, 2, 3, 4A, 4B, 5, 6

  • center and surround antagonistic RF similar to LGN
  • orientation selectivity
  • direction selectivity

NEURO 0010 (22 decks)

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