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SMP - Neurophysio Exam 2 > Lectures 7 & 8 - Central Visual Pathways > Flashcards

Lectures 7 & 8 - Central Visual Pathways Flashcards

1
Q

In which central visual pathway structures are the receptive field properties of the retina inherited? What is this called?

A 
Monocular cells (LGN, V1) and binocular cells (V1 and extrastriate)
 => Retinotopy
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2
Q

What is the central visual pathway?

A

Retina => optic nerves => optic chiasm => optic tracts => LGN => optic radiations => primary visual cortex => extrastriate cortex => PPC or temporal lobe

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3
Q

What is another name for the central visual pathway?

A

Retinofugal pathway

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4
Q

What is each optic nerve composed of?

A

Afferents from only one eye

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5
Q

What is each optic tract composed of?

A

Afferents from both eyes:

  • Temporal retina of ipsilateral eye
  • Nasal retina of contralateral eye
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6
Q

Result of small lesion to optic nerve? 2 names

A

Monocular selective blindness = scotoma: partial loss of vision or a blind spot in an otherwise normal visual field

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7
Q

Result of transection of optic nerve?

A

Monocular blindness

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8
Q

Result of optic chiasm lesion?

A

Bitemporal blindness

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9
Q

What is anopsia?

A

Specific blindness within the visual field

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10
Q

What is the primary target of the optic tracts?

A

LGN (thalamus)

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11
Q

What are 3 other targets of the optic tracts? Purpose?

A
  1. Hypothalamus: suprachiasmatic nucleus for daily biological rythms
  2. Midbrain: pretectal nucleus for constriction of the pupil and accommodation of the lens
  3. Midbrain: superior colliculus for movement of the head in response to light
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12
Q

Are LGN cells monocular or binocular?

A

Monocular

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13
Q

How are the cells organized in the LGN?

A

Layers according to which eye they receive input from and from what type of RGC

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14
Q

How are receptive field characteristics of the retina inherited by the cells of the LGN?

A

Each cell only receives input from either M-type, P-type, or nonM-nonP-type RGCs

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15
Q

How are the layers of the cells in the LGN numbered?

A

Most superficial layer is layer 1

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16
Q

What do we call LGN cells that receive input from P-type RGCs?

A

Parvocellular

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17
Q

What do we call LGN cells that receive input from M-type RGCs?

A

Magnocellular

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18
Q

What do we call LGN cells that receive input from nonM-nonP-type RGCs?

A

Koniocellular

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19
Q

Where are LGN cells that receive input from nonM-nonP-type RGCs located? From what eye do they receive input?

A

Ventral to each principal layer and receive input from the same eye as the overlying principal layer

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20
Q

Where is the striate cortex located?

A

Occipital lobe (area 17)

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21
Q

Describe the structure of the striate cortex.

A

Laminar structure with 6 principal cell layers (I-VI) and additional sub-layers

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22
Q

Who has a larger striate cortex: primates or humans?

A

Primates

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23
Q

What is the calcarine fissure?

A

Located on the medial surface of the occipital lobe and divides the visual cortex into two

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24
Q

What is the major input layer of the striate cortex?

A

Layer IVC

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25
Q

From what cells does layer IVC of the striate cortex receive input?

A
  1. Magnocellular LGN

2. Parvocellular LGN

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26
Q

From what cells do other layers of the striate cortex receive input?

A

Koniocellular LGN

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27
Q

How are cells in layer IVC of the striate cortex organized?

A

Organized into monocular dominance columns (each column receives input from the same eye)

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28
Q

How were monocular cell layers of the LGN and ocular dominance columns of the IVC layer of the striate cortex identified?

A

Radioactive tracing

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29
Q

Layer 1 of LGN:

  1. Ipsilateral or contralateral visual input?
  2. Type of RGC?
A
  1. Contralaterial

2. Magnocellular

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30
Q

Layer 2 of LGN:

  1. Ipsilateral or contralateral visual input?
  2. Type of RGC input?
A
  1. Ipsilateral

2. M-type

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31
Q

Layer 3 of LGN:

  1. Ipsilateral or contralateral visual input?
  2. Type of RGC?
A
  1. Ipsilateral

2. P-type

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32
Q

Layer 4 of LGN:

  1. Ipsilateral or contralateral visual input?
  2. Type of RGC?
A
  1. Contralateral

2. P-type

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33
Q

Layer 5 of LGN:

  1. Ipsilateral or contralateral visual input?
  2. Type of RGC?
A
  1. Ipsilateral

2. P-type

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34
Q

Layer 6 of LGN:

  1. Ipsilateral or contralateral visual input?
  2. Type of RGC?
A
  1. Contralateral

2. P-type

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35
Q

What is layer IV of the striate cortex divided into?

A

Layers a, b, c alpha, c beta

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36
Q

Where do magnocellular LGN neurons project?

A

Layer IV c alpha of striate cortex

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37
Q

Where do parvocellular LGN neurons project?

A

Layer IV c beta of striate cortex

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38
Q

Where do koniocellular LGN neurons project?

A

Layers II and III of striate cortex

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39
Q

How many layers in the striate cortex?

A

6

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40
Q

What do the cells of the striate cortex that receive input from kionocellular LGN neurons form?

A

Monocular cells organized in blobs

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41
Q

Describe the binocular cells of the striate cortex. Where are they located?

A

Cells that receive converging output from monocular cells in layer IV c ocular dominance columns (alpha and beta) located in interblob regions

42
Q

Describe the receptive field characteristics of binocular cells of the striate cortex.

A

Orientation selective cells, meaning they respond maximally to a bar of light at a specific orientation in their receptive field

43
Q

What are the 2 types of binocular striate cortex cells?

A
  1. M-type

2. P-type

44
Q

Can a binocular striate cortex cell receive input from both magnocellular and parvocellular cells of layer IV?

45
Q

Which layers of the striate cortex have interblob regions?

A

All except IVC

46
Q

Describe direction selective cells of the striate cortex.

A

Subset of M-type orientation selective cells that are ALSO direction sensitive, meaning they respond they respond maximally to a bar of light moving in a direction perpendicular to the preferred orientation

47
Q

What are the 3 central visual pathways originating at the RGCs of the retina? What can be said about how they relate to each other?

A
  1. Magnocellular pathway
  2. Blob pathway
  3. Parvo-interblob pathway

They are parallel (but not perfectly)

48
Q

What is another name for the blob pathway?

A

Koniocellular

49
Q

Function of magnocellular pathway?

A

Analysis of motion

50
Q

Function of blob pathway?

A

Analysis of color

51
Q

Function of parvo-interblob pathway?

A

Analysis of shape

52
Q

Which central visual pathway(s) constitute the ventral stream?

A
  1. Blob pathway

2. Parvo-interblob pathway

53
Q

Which central visual pathway(s) constitute the dorsal stream?

A

Magnocellular pathway

54
Q

Describe the magnocellular pathway.

A

M-type RGCs in retina => magnocellular LGN cells in layers 1 and 2 => monocular cells in layer IV C alpha of striate cortex => Direction selective binocular cells AND unicular cells of the striate layers outside IVC => extrastriate cortical areas

55
Q

Describe the blob pathway.

A

nonM-nonP type RGCs in retina => koniocellular LGN cells in between layers of LGN + layers IV C alpha and beta of striate=> monocular cells in blobs of striate cortex outside IVC => extrastriate cortical areas

56
Q

Describe the parvo-interblob pathway.

A

P-type RGCs in retina => parvocellular LGN cells in layers 3-6 => monocular cells in layer IV C beta of striate cortex => orientation selective binocular cells AND unicular cells of the striate layers outside IVC => extrastriate cortical areas

57
Q

Where is the extrastriate cortex?

A

Occipital lobe

58
Q

Describe the 2 extrastriate pathways.

A

Extrastriate cortex => dorsal “where” pathway to posterior parietal cortex OR ventral “what” pathway to inferior temporal lobe

59
Q

Function of dorsal pathway?

A

Analysis of visual motion and visual control of motor action

60
Q

Function of ventral pathway?

A

Object recognition

61
Q

What are the receptive field characteristics of the dorsal extrastriate pathway?

A
  1. Direction selective cells
  2. Radial motion cells
  3. Circular motion cells
62
Q

What are the receptive field characteristics of the ventral extrastriate pathway?

A
  1. Color selective cells

2. Orientation selective cells

63
Q

What are the symptoms of damages to the dorsal extrastriate stream?

A

Deficits in:

  1. Spatial orientation
  2. Motion detection
  3. Guidance of visual tracking eye movements
64
Q

What are the symptoms of damages to the ventral extrastriate stream?

A

Deficits in:

  1. Complex visual perception tasks
  2. Attention
  3. Learning/memory
65
Q

What 2 particular conditions can result from damage to the ventral extrastriate stream?

A
  1. Cerebral achromatopsia

2. Prosopagnosia

66
Q

What is cerebral achromatopsia?

A

Type of color-blindness caused by damage to the ventral extrastriate stream, rather than abnormalities in the cells of the eye’s retina.

67
Q

What is prosopagnosia?

A

Damage to fusiform face area in the inferior temporal lobe leading to face blindness

68
Q

What kind of neurons are found in the striate cortex?

A

Pyramidal, except for the ones in layer IV

69
Q

What 2 factors is the initial development of the organized visual system dependent on?

A
  1. Prenatal chemical signals (e.g. ephrins)

2. Prenatal spontaneous activity with Hebbian plasticity

70
Q

What is the maintenance of the organized visual system dependent on?

A

Normal visual experience during the postnatal sensitive period to trigger experience (activity) dependent plasticity and compare relative activity levels between eyes

71
Q

What is Hebbian plasticity?

A

Cells that wire together must first fire together = only synapses in which depolarization is concurrent in the presynaptic and postsynaptic element are maintained

72
Q

What kind of receptors mediate Hebbian plasticity? Describe each.

A

Ionotropic glutamate receptors:

  1. AMPA receptors: Na+ permeable
  2. NMDA receptors: Ca++ and Na+ permeable with a unique Mg++ block removed by AMPA mediated depolarization
73
Q

What is LTP?

A

Calcium influx through NMDA channels opened by AMPA mediated depolarization causes activation of CamK II to mediate AMPA receptor insertion to make the postsynaptic membrane more sensitive to glutamate

74
Q

What is another name for LTP?

A

AMPAfication

75
Q

How is LTP induced?

A

High frequency stimulation

76
Q

Which neurons are more susceptible to LTP: neurons with only NMDA receptors or neurons with both NMDA and AMPA receptors?

A

Neurons with both NMDA and AMPA receptors

77
Q

What are the 3 characteristics of LTP? Explain each.

A
  1. State dependent: state of postsynaptic membrane potential determines whether or not LTP will occur (it’ll only occur if postsynaptic depolarization occurs within 100 ms of presynaptic depolarization)
  2. Specific: when LTP is induced at active synapses it does not occur at inactive synapses at the same cell (inactive synapses are subject to LTD)
  3. Associative: if a synapse is weakly active at the same time another synapse onto the same neuron undergoes LTP, both synapses will undergo LTP
78
Q

What is synaptic weakening?

A

LTD: lack of correlated pre and postsynaptic activity => low NMDA mediated Ca++ influx => removal of AMPA receptors => synapse silencing and depression => removal during development

79
Q

What is LTD during development called?

A

Neural pruning

80
Q

What is LTD modulated by?

A

Calcineurin and protein phosphatase 1

81
Q

What is calcineurin?

A

Calcium and calmodulin dependent serine/threonine protein phosphatase

82
Q

LTD Ca++ rise?

83
Q

LTP Ca++ rise?

84
Q

Are NMDARs activated in both LTP and LTD?

85
Q

What is the sensitive (critical) period in cats?

A

3rd week to 3 months

86
Q

What is the sensitive (critical) period in monkeys?

A

0 to 6 months

87
Q

What is the sensitive (critical) period in humans?

A

0 to 1 year (most critical) but extends to 5-10 years old

88
Q

What are the effects of monocular deprivation postnatally?

A
  • The eye not receiving stimulation will be less represented in the cortex (shrunken ocular dominance column)
  • The eye receiving stimulation will be more widely represented in cortex (expanded ocular dominance column): basically compensation
89
Q

What are the 2 forms of activity dependent plasticity?

A
  1. Hebbian plasticity

2. Experience dependent plasticity

90
Q

What do bright lines on images about ocular deprivation mean?

A

Cells received signal (aka tracer)

91
Q

Does the normal central visual pathway have about the same allocation of neurons for both eyes?

92
Q

What could lead to monocular deprivation?

A

Monocular congenital cataract

93
Q

What happens if ocular deprivation extends past the critical developmental period?

A

Alterations to the visual system will

be permanent

94
Q

Effect of binocular deprivation?

A

No relative changes to ocular dominance columns because the visual system compares relative activity in each eye, BUT shrinking of all layers due to decrease innervation

95
Q

Do binocular cells of V1 receive input for kionocellular LGN?

96
Q

Does the blob pathway have any binocular cells

97
Q

Do all striate cortex layer other than 4C have interblob regions?

98
Q

From which 3 places do striate blobs receive input?

A
  1. Koniocellular LGN cells (layers II and III)

2. Layers IV C alpha and beta of striate

99
Q

Which cells are hyperactive in acromegaly/gigantism? What are the 2 types? Describe each.

A

Acidophil cells of the anterior pituitary:

  1. Somatotrophs secrete somatotropin/GH
  2. Mammotrophs secrete prolactin
100
Q

Result of transection of optic tract?

A

Homonymous hemianopsia

101
Q

Result of transection of optic radiations?

A

Left homonymous hemianopsia

SMP - Neurophysio Exam 2 (9 decks)

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