Primary visual pathway: visual field representations Flashcards
1
Q
what does the vertical meridian split
A
- the entire visual field into two:
a right half field and a left half field - the retina into half
a nasal half and a temporal half
2
Q
what happens to the ganglion cells as a result of the retina being split in half by the vertical meridian
A
Nasal ganglion cells cross and temporal ganglion cells do not cross the midline
3
Q
beyond the optic chiasm, which side on the visual field is represented by which side of the brain
A
left side of visual field is represented by the right side of the brain
right side of visual field is represented by the left side of the brain
4
Q
what is the primary visual pathway map of the retina called
A
retinotopic map
5
Q
what is the primary visual pathway map of the visual field called
A
visuotopic map
6
Q
what is the name of the vertical line which splits the retina into nasal and temporal
A
line of decussation
7
Q
how large is the macula in diameter
A
5mm
8
Q
how much of central vision does the macula represent
A
15 degrees
9
Q
how large is the fovea centralis in diameter
A
1.5mm
10
Q
how much of central vision does the fovea centralis represent
A
3 degrees
11
Q
how much of the ganglion cells of the retina does the macula and fovea centralis have together
A
66-75%
12
Q
which regions are over represented in the visual system
A
macula & fovea centralis
13
Q
how much of the territory in the primary visual pathways is devoted to processing information from the macula and fovea centralis ganglion cells
A
66-75%
14
Q
which region of the retina do blood vessels and ganglion cells skirt around and why
A
the fovea
to reduce light scatter & increase visual resolution/acuity
15
Q
what part of the retina do ganglion cells axons run in
A
the nerve fibre layer of the inner retina
16
Q
which type of order to axons have as they leave the eye
A
retinotopic order
17
Q
what does the retinotopic order do
A
maintain the map of the retina as axons dive out of the ONH
18
Q
which parts of the retina does the retinotopic map run from
A
periphery to central
19
Q
at which area of the ONH does the axons of the peripheral superior, nasal, inferior & temporal quadrants of the retina enter
A
peripheral part of ONH
20
Q
at which part of the ONH does the axons of the central retina enter
A
central part of ONH
21
Q
which region of the retina has the highest ganglion cell density
A
papillomacular bundle
22
Q
what does the intermediate part of the retina look at
A
intermediate location
23
Q
what does the peripheral part of retina look at
A
peripheral space
24
Q
what does the central part of the retina look at
A
central space
25
at which region of the ONH do the fovea & macula axons (papillomacular bundle axons) start
temporal at the ONH
26
which region do the fovea & macula axons move when they reach the nerve and chiasm
more central or medial
27
which region do the fovea & macula axons move when they reach the optic tract
dorsally into deeper part of optic tract
28
where within the chiasm are the nasal inferior axons found
at the base of the chiasm, above the pituitary gland
29
describe the arrangement of the axons in the optic nerve head
they are separated by connective tissue & astrocyte septa into several 100 groups or fascicles, with mixed midget/parvo & parasol/magno cell axons
30
at which region of the optic pathway does the axons change to a non-fascicular organisation
optic tract
31
how are the axons arranged in the optic tract
spread out over surface of tissue
32
where are the smaller diameter midget/parvo axons mainly found within the optic tract
deepest within the tissue (bottom)
33
where are the larger diameter mango/parasol axons mainly found within the optic tract
nearer the pial surface (top)
34
why is there a segregation of the magno and midget ganglion cell axons in the optic tract
they are lined up ready to terminate in the different layers of the LGN
35
which layers of the LGN do the midget/parvo ganglion axons terminate
3,4,5,6 (top of LGN)
36
which layers of the LGN do the magno/parasol ganglion axons terminate
1 & 2 (bottom of LGN)
37
which part of the optic pathway does the fascicular organisation start to break down
optic chiasm
38
what happens to the nasal half of each retina axons at the optic chiasm
cross the midline = decussate
39
which layers of the LGN do the nasal axons from the opposite eye terminate
1, 4 & 6
40
which layers of the LGN do the temporal axons from the same (ipsilateral) eye terminate
2, 3 & 5
41
why do the nasal axons from the opposite eye terminate in layers 1,4&6 and temporal axons from the same eye terminate in layers 2,3&5 of the LGN
so that each of the 6 layers of the LGN contains its own map of the opposite hemi-field originating from one eye
42
what is another LGN function
to organise retinal inputs from the 2 eyes
- into alternating maps of the opposite hemi-field
- one in each of its 6 layers
43
why does the LGN organise inputs from the 2 eyes into alternating maps of the opposite hemi field, one in each of its 6 layers
because it relays these maps on to the v1 cortex
44
which side of the brain does the relayed retinal inputs of maps on the v1 cortex go
on the same side (ipsilateral) side of the brain
| e.g. right LGN connects to right visual cortex in occipital lobe
45
what do the maps travel via to reach the v1 cortex
axons that arise from the LGN neurons in each layer
46
where do the axons which arise from the LGN neurons in each layer travel in first
in the posterior limb of the internal capsule (white matter pathway)
47
where do the axons which arise from the LGN neurons in each layer which first go in the posterior limb of the internal capsule travel in after
in the optic radiations to area v1
48
what is the name of the pathway where the axons which arise from the LGN that go in the posterior limb of the internal capsule and then in the optic radiations to area v1 called
geniculo-cortical pathway
49
what do stumps of right and left optic nerve come together at
optic chiasm
50
what do the optic tracts go towards
LGN
51
what does the LGN sit laterally besides
thalamus
52
what does the internal capsule contain
fascicles of LGN axons
53
what is sitting infront of the posterior limb go the internal capsule
2 nuclei
| which are part of the basal ganglia
54
what are the names of the two nuclei which sit infront of the posterior limb of the internal capsule
globus pallidus
&
putamen
55
what do the globus pallidus and putamen nuclei both form collectively
the lentiform nucleus
56
what shape does the lentiform nucleus resemble
lens shape
57
the internal capsule consists of two limbs and a bend called the..
genu (bend in-between the two limbs)
58
which axons of the posterior limb of the internal capsule are the most posterior
geniculo-cortical axons
59
which region do the geniculo-cortical axons of the posterior limb of the internal capsule run before entering the optic radiations
retro-lenticular region
60
what do the geniculo-cortical axons coming from the thalamus run as which goes towards the occipital lobes
optic radiations
61
describe the sequence of which the connections between the thalamus and the 3 major lobes (frontal, parietal & occipital) which have axons that run through the different parts of the internal capsule
- connections from frontal cortex run front the frontal part of the internal capsule known as anterior limb & genu
- connections with parietal lobe run in first part of posterior limb & occipital cortex come from most posterior part of posterior limb of internal capsule
62
what is the region of the internal capsule through which these optic cortico-geniuclo axons run called
retro-lenticular region of internal capsule
63
why is the retro-lenticular region of the internal capsule called retro-lenticular
because it sits behind the lenticular nucleus which is formed by the globus pallidus & putamen nuclei
64
why does the inferior horn of the lateral ventricle cause a problem
it has a split and a space to CSF which is in the way
65
what is the reason for the split in the inferior horn of the lateral ventricle
axons coming from the medial half of the LGN, which represents the lower visual quadrant of the hemifield map are able to pass straight over it to enter the optic radiations directly,
but
it forms an obstruction to axons coming from the lateral half of the LGN, which represents the upper visual quadrant of the hemifield map,
so
they are initially forced to travel anteriorly & then loop around it to join the optic radiations
66
which visual quadrant of the hemifield map do axons from the medial half of the LGN represent
lower
67
which visual quadrant of the hemifield map do axons from the lateral half of the LGN represent
upper
68
from where to where do the axons from the lower visual quadrant run
from: over the inferior horn of the lateral ventricle & below the parietal lobe
to: straight to the upper bank of the calcarine sulcus
69
from where to where do the axons from the upper visual quadrant run
from: meyer's loop around the inferior horn of the internal ventricle, below the temporal lobe
to: the lower bank of the calcarine sulcus
70
why is the hemi-field map in area v1 cortex inverted
the lower visual quadrant is represented in the upper bank of the calcarine sulcus
&
the upper visual quadrant (via meyer's loop) is represented in the lower bank of the calcarine sulcus
71
why is the semi-field map in area v1 cortex distorted
because 66-75% of the posterior region on both banks of the calcarine sulcus is devoted to over representing the fovea & macula (central vision). with more peripheral vision anteriorly of the calcarine sulcus (towards the parieto-occipital sulcus)
72
what does the horizontal meridian split
the lower from the upper visual quadrant
73
what supplies blood to the axons in the first part of radiations (lenticular region) after the internal capsule
middle cerebral artery (MCA)
74
what is the middle cerebral artery a branch of
internal carotid artery
75
what supplies blood to the axons in the last part of the radiations, under the occipital lobe
posterior cerebral artery (PCA)
76
what is the posterior cerebral artery a branch of
terminal branch of basilar artery
77
what supplies blood to the calcarine sulcus, upper & lower banks and into the depth of the fundus
calcarine artery
78
what is the calcarine artery a terminal branch of
posterior cerebral artery
79
what is the blood supply to the occipital pole (fovea/macula vision)
a dual supply
- the calcarine artery
&
- a terminal branch of the MCA
80
what does a lesion within the white matter, axons (where myelinated axons are travelling) e.g. optic pathway or radiations cause
prevents or slows down impulse conduction
81
what are the causes of a lesion to the white matter, where myelinated axons are travelling e.g. optic pathway or radiations
- infection, inflammation eg de-myelination (eg multiple sclerosis)
- trauma, compression by traumas
- vascular lesions (blockage, haemorrhage)
82
what does a lesion within the grey matter, neurons (e.g. LGN or v1 cortex) cause
kills cells which can't be replaced (this causes visual field loss)
83
what are the causes of a lesion to the grey matter, neurons e.g. LGN or v1 cortex
- infection, inflammation (eg encephalitis which kills neurons in the grey matter)
- trauma, compression by tumours
- vascular lesions (blockage, haemorrhage)
84
what visual field loss occurs if there is a lesion which cuts through the entire optic nerve of the right eye or if a lesion prevents axons within the right optic nerve from signalling information to the brain because the axons have demyelinated
all vision will be lost in right eye
85
what visual field loss occurs if there is a lesion of the optic chiasm, which has split the chiasm into two, so that the nasal axons of the left and right eyes do not signal to the brain
a bi-temporal hemianopia
86
what can be the cause of a bi-temporal hemianopia (lesion to the nasal axons at the optic chiasm)
tumour of pituitary gland that is growing upwards
87
what visual field loss occurs when there is a lesion to the optic tract of the right side of the brain, (after the nasal axons of the left eye have crossed over & the temporal axons of the right eye are uncrossed)
left hemianopia (loss of visual field of left side)
88
what can be the cause of a hemianopia (lesion to the optic tract on opposite side of brain)
branches of the PCA which supply the optic tract can be blocked or haemorrhaged and can lose axons of the optic tract
89
what visual field loss occurs when theres a lesion of only the right meyer's loop (and the direct components are intact) of the optic radiations
upper left quadrantanopsia
90
why is there only an upper left quadrantanopsia caused when there is damage to the opposite meyer's loop
if the damage is on the right side of the brain, then there will be problems on the left side of visual field, but only the upper quadrant in the left & right eye will have the visual field loss, because its the upper quadrant which meyer's loop is conveying in the v1 cortex which are gone
91
what visual field loss occurs when a lesion wipes out the whole of the v1 cortex on the right side
left hemianopia, BUT the macula and fovea on the left side are spared
92
what can cause a lesion which wipes out the whole of one side of the v1 cortex
posterior cerebral artery can be blocked so there will be no blood flow to the tissue of the calcarine sulcus, or the neurones are dead so v1 on that side is gone
93
of which artery does an infarct spare the macula and fovea on the left side
PCA infarct
94
what is the vertical meridian dividing
the line dividing the visual field into 2 halves
95
where is the vertical meridian dividing line represented
the border between areas v1 and v2
96
what is the horizontal dividing
the line dividing the upper from lower visual quadrants
97
where is the horizontal meridian dividing line represented
in the fundus of the calcarine sulcus
