Lectures 7 & 8 - Central Visual Pathways Flashcards Preview

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

Flashcards in Lectures 7 & 8 - Central Visual Pathways Deck (101):
1

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

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

2

What is the central visual pathway?

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

3

What is another name for the central visual pathway?

Retinofugal pathway

4

What is each optic nerve composed of?

Afferents from only one eye

5

What is each optic tract composed of?

Afferents from both eyes:

- Temporal retina of ipsilateral eye
- Nasal retina of contralateral eye

6

Result of small lesion to optic nerve? 2 names

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

7

Result of transection of optic nerve?

Monocular blindness

8

Result of optic chiasm lesion?

Bitemporal blindness

9

What is anopsia?

Specific blindness within the visual field

10

What is the primary target of the optic tracts?

LGN (thalamus)

11

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

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

12

Are LGN cells monocular or binocular?

Monocular

13

How are the cells organized in the LGN?

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

14

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

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

15

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

Most superficial layer is layer 1

16

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

Parvocellular

17

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

Magnocellular

18

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

Koniocellular

19

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

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

20

Where is the striate cortex located?

Occipital lobe (area 17)

21

Describe the structure of the striate cortex.

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

22

Who has a larger striate cortex: primates or humans?

Primates

23

What is the calcarine fissure?

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

24

What is the major input layer of the striate cortex?

Layer IVC

25

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

1. Magnocellular LGN
2. Parvocellular LGN

26

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

Koniocellular LGN

27

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

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

28

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

Radioactive tracing

29

Layer 1 of LGN:
1. Ipsilateral or contralateral visual input?
2. Type of RGC?

1. Contralaterial
2. Magnocellular

30

Layer 2 of LGN:
1. Ipsilateral or contralateral visual input?
2. Type of RGC input?

1. Ipsilateral
2. M-type

31

Layer 3 of LGN:
1. Ipsilateral or contralateral visual input?
2. Type of RGC?

1. Ipsilateral
2. P-type

32

Layer 4 of LGN:
1. Ipsilateral or contralateral visual input?
2. Type of RGC?

1. Contralateral
2. P-type

33

Layer 5 of LGN:
1. Ipsilateral or contralateral visual input?
2. Type of RGC?

1. Ipsilateral
2. P-type

34

Layer 6 of LGN:
1. Ipsilateral or contralateral visual input?
2. Type of RGC?

1. Contralateral
2. P-type

35

What is layer IV of the striate cortex divided into?

Layers a, b, c alpha, c beta

36

Where do magnocellular LGN neurons project?

Layer IV c alpha of striate cortex

37

Where do parvocellular LGN neurons project?

Layer IV c beta of striate cortex

38

Where do koniocellular LGN neurons project?

Layers II and III of striate cortex

39

How many layers in the striate cortex?

6

40

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

Monocular cells organized in blobs

41

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

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

42

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

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

43

What are the 2 types of binocular striate cortex cells?

1. M-type
2. P-type

44

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

NOPE

45

Which layers of the striate cortex have interblob regions?

All except IVC

46

Describe direction selective cells of the striate cortex.

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

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?

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

They are parallel (but not perfectly)

48

What is another name for the blob pathway?

Koniocellular

49

Function of magnocellular pathway?

Analysis of motion

50

Function of blob pathway?

Analysis of color

51

Function of parvo-interblob pathway?

Analysis of shape

52

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

1. Blob pathway
2. Parvo-interblob pathway

53

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

Magnocellular pathway

54

Describe the magnocellular pathway.

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

Describe the blob pathway.

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

Describe the parvo-interblob pathway.

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

Where is the extrastriate cortex?

Occipital lobe

58

Describe the 2 extrastriate pathways.

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

59

Function of dorsal pathway?

Analysis of visual motion and visual control of motor action

60

Function of ventral pathway?

Object recognition

61

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

1. Direction selective cells
2. Radial motion cells
3. Circular motion cells

62

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

1. Color selective cells
2. Orientation selective cells

63

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

Deficits in:
1. Spatial orientation
2. Motion detection
3. Guidance of visual tracking eye movements

64

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

Deficits in:
1. Complex visual perception tasks
2. Attention
3. Learning/memory

65

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

1. Cerebral achromatopsia
2. Prosopagnosia

66

What is cerebral achromatopsia?

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

67

What is prosopagnosia?

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

68

What kind of neurons are found in the striate cortex?

Pyramidal, except for the ones in layer IV

69

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

1. Prenatal chemical signals (e.g. ephrins)
2. Prenatal spontaneous activity with Hebbian plasticity

70

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

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

71

What is Hebbian plasticity?

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

72

What kind of receptors mediate Hebbian plasticity? Describe each.

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

What is LTP?

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

What is another name for LTP?

AMPAfication

75

How is LTP induced?

High frequency stimulation

76

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

Neurons with both NMDA and AMPA receptors

77

What are the 3 characteristics of LTP? Explain each.

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

What is synaptic weakening?

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

What is LTD during development called?

Neural pruning

80

What is LTD modulated by?

Calcineurin and protein phosphatase 1

81

What is calcineurin?

Calcium and calmodulin dependent serine/threonine protein phosphatase

82

LTD Ca++ rise?

Small

83

LTP Ca++ rise?

Large

84

Are NMDARs activated in both LTP and LTD?

YUP

85

What is the sensitive (critical) period in cats?

3rd week to 3 months

86

What is the sensitive (critical) period in monkeys?

0 to 6 months

87

What is the sensitive (critical) period in humans?

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

88

What are the effects of monocular deprivation postnatally?

- 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

What are the 2 forms of activity dependent plasticity?

1. Hebbian plasticity
2. Experience dependent plasticity

90

What do bright lines on images about ocular deprivation mean?

Cells received signal (aka tracer)

91

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

YUP

92

What could lead to monocular deprivation?

Monocular congenital cataract

93

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

Alterations to the visual system will
be permanent

94

Effect of binocular deprivation?

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

Do binocular cells of V1 receive input for kionocellular LGN?

NOPE

96

Does the blob pathway have any binocular cells

NOPE

97

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

YUP

98

From which 3 places do striate blobs receive input?

1. Koniocellular LGN cells (layers II and III)
2. Layers IV C alpha and beta of striate

99

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

Acidophil cells of the anterior pituitary:
1. Somatotrophs secrete somatotropin/GH
2. Mammotrophs secrete prolactin

100

Result of transection of optic tract?

Homonymous hemianopsia

101

Result of transection of optic radiations?

Left homonymous hemianopsia