Visual Pathways Flashcards
1
Q
What is the cornea?
A
Clear protective outer layer
2
Q
What is the iris?
A
- Thin circular structure that controls diameter of the pupil
- Defines eye color
3
Q
What is the pupil?
A
Hole in center of the iris that allows light to enter
4
Q
What is the lens?
A
As light passed through the cornea and the lens refraction occurs to form the image on the retina
5
Q
What is the vitreous body?
A
Clear, gel like structure between the lens and the retina
6
Q
What is the retina?
A
- Layer of cells lining the back wall inside the eye
- Senses light and sends signals to the brain so you can see
7
Q
What is the fovea?
A
Region of the retina with highest visual acuity
8
Q
What is the macula?
A
- An oval region (3 x 5 mm) that surrounds the fovea
- Relatively high visual acuity
9
Q
What is the optic disc?
A
- Region where the axons leaving the retina gather to form the optic nerve
- No photo receptors
10
Q
Which cranial nerve is the optic nerve?
A
CN II
11
Q
What is the formation of images on the retina?
A
Optical properties of the lens invert and reverse projection of the visual image on the retina
12
Q
Where is the central fixation point for each eye?
A
Fovea
13
Q
The optic disc sits 15° medial (nasal) to the ?
A
Fovea
14
Q
Since the optic disc sits 15° medial to the fovea what does this create?
A
small blind spot 15° lateral and slightly inferior to the central fixation point for each eye
15
Q
If you had both eyes open can you tell your eye has a blind spot? Why or why not?
A
- Blind spots for the two eyes are not superimposed
- No functional deficit
16
Q
If you only have one closed are you aware of blind spot? Why or why not?
A
- Unaware of blind spot
- Visual analysis pathways “fill in” blind spot
17
Q
Which is more numerous rods or cones?
A
Rods
18
Q
What is the main function of rods?
A
Vision in low lighting conditions
19
Q
Do rods or cones detect color?
A
Cones
20
Q
Which has relatively poor spatial and temporal resolution? Rods or Cones?
A
Rods
- Cones have relatively high spatial and temporal resolution
21
Q
Cones are highly represented in the ?
A
Fovea (visual acuity)
22
Q
Cones detect (blank) types that contain (blank) form of pigment?
A
3 & 3
- Each absorbs light from a different part of the spectrum
23
Q
What forms the outermost layer of the retina?
A
Photoreceptors
24
Q
In order for light to reach photoreceptors in must travel through?
A
All layers
25
T/F: All other layers of the retina are present in the fovea
F: They are not present which allows light to reach receptors without distortion
26
The cells of the visual pathway are activated by what? What is the order of synapse?
- Activated by light
Photoreceptors synapse on bipolar cells, bipolar cells synapse on ganglion cells, axons of ganglion cells sent into optic nerve
27
Photoreceptors and bipolar cells do not fire action potentials, so how is information conveyed?
- Via passive electrical conduction
- Nontraditional synapse release neurotransmitter in a graded fashion dependent upon membrane potential
28
How do ganglion cells convey information?
- Fire action potentials
- Convey information into the optic nerve
29
What are the 2 types of interneurons?
- Horizontal cells
- Amacrine Cells
30
Light on the retina has one effect on the bipolar and ganglion cells directly in its path and the opposite effect on the (BLANK) bipolar and ganglion cells
Light on the retina has one effect (inhibition or excitation) on the bipolar and ganglion cells directly in its path and the opposite effect (excitation or inhibition) on the surrounding bipolar and ganglion cells
31
What happens to on center cells when light hits them?
- Center of receptive field is Excited by light
- Surrounding area is Inhibited by light
32
What happens to off center cells when light hits them?
-Center of receptive field is inhibited by light
- Surrounding area is Excited by light
33
Parasol cells have (BLANK) cell bodies, receptive (dendritic) fields and, diameter fibers
Large
34
Midget cells have (BLANK) cell bodies, receptive (dendritic) fields, and diameter fibers.
Small
35
What does parasol cells respond best to?
Gross stimulus features and movement
36
What are midget cells sensitive to?
Fine visual details and to colors
37
Where do parasol cells project?
Project to magnocellular layers of the lateral geniculate nucleus of the thalamus
38
Where do midget cells project?
Project to parvocellular layers of the lateral geniculate nucleus of the thalamus
39
What forms the optic nerve and where do they meet?
- Formed by retinal ganglion cells
- L & R optic nerves meet at the optic chiasm
40
What fibers cross at the optic chiasm?
- Partial crossing of fibers
- Medial (nasal) retinal fibers for each eye cross
41
What is the L optic tract and what information does it carry?
- Fibers from the left hemiretina of both eyes
- Carries information from the R visual field
42
What is the R optic tract and what information does it carry?
- Fibers from the right hemiretina of both eyes
- Carries information for the L visual field
43
What is the optic chiasm susceptible to?
Compression by pituitary tumors and other lesions in the area
44
What two distinct pathways are supplied by the optic tract?
- Geniculate Pathway
- Extrageniculate Pathway
45
Where does the geniculate pathway synapse?
Synapses in lateral geniculate nucleus of the thalamus
46
Where does the extrageniculate pathway synapse?
Synapses in superior colliculus and pretectal areas of the midbrain
47
Where does the geniculate pathway relay information to?
Relay to primary visual cortex via optic radiations
48
What is the function of the geniculate pathway?
Visual discrimination and perception
49
Where does the extrageniculate pathway project?
- Projects to pulvinar and lateral posterior nucleus of the thalamus
- Projects to lateral parietal cortex and frontal eye fields
50
What is the function of the extrageniculate pathway?
Direct visual attention and eye movement towards stimuli
51
The lateral geniculate nucleus has 6 layers numbered ventral to dorsal what is the name of layers 3-6 and layers 1-2?
Layers (3-6): Dorsal Parvocellular layers
Layers (1-2): Ventral Magnocellular Layers
52
Dorsal Parvocellular layers input is from? And what information gets relayed?
- Input from retinal ganglion midget cells
- Relay information for form and color
53
Ventral Magnocellular Layers input is from where? What information gets relayed?
- Input from retinal ganglion parasol cells
- Relay information for motion & spatial analysis
54
Both layers of the lateral geniculate nucleus keep info from R & L (BLANK)
Segregated
55
What are optic radiations?
Axons traveling from LGN to primary visual cortex
56
Inferior optic radiations (Meyer's Loop) information is from where? Where do they terminate?
- Information from inferior retina (superior visual field)
- Arc into temporal lobe
- Terminate inferior to calcimine fissure (lingula)
57
Superior (Upper) optic radiations information is from where? Where do they terminate?
- Information from superior retina (inferior visual field)
- Pass under the parietal lobe
- Terminate superior to calcarine fissure (cuneus)
58
Where is the fovea represented?
- Make up what percent of visual cortex?
- Why is fovea disproportionately represented?
- Represented at the occipital pole (medial and lateral)
- 50% of visual cortex
- Fovea is disproportionately represented based on size due to high photoreceptor density
59
Where is the peripheral retina represented?
More anteriorly along the calcarine fissure
60
Where does most input to the primary visual cortex arrive in the neocortex?
Layer 4
61
In the neocortex layer 4 is subdivided into which sublaminae?
4A, 4B, 4C alpha and 4C beta`
62
Layer 4B contain numerous myelinated axon resulting in what?
Pale appearance called stria of Gennari
63
What is another name for the primary visual cortex?
Striate cortex
64
Describe 4B
- contains myelinated axon collaterals (Stria of Gennari)
- gives name striate cortex
65
Describe 4C alpha
- Input from magnocellular layers of LGN
- Information about movement and gross spatial features
66
Describe 4C beta
- Input from parvocellular layers of LGN
- Fine spatial information
67
Describe the parallel channel to process motion/spatial analysis
Parasol cells --> magnocellular layers --> layer 4C alpha --> layer 4B --> thick stripe --> dorsolateral Parieto-occipital cortex
68
Describe the parallel channel to process form
Midget cell --> parvocellular layers --> layer 4C beta --> Layer 2,3 interblobs --> pale stripe --> inferior occipitotemporal cortex
69
Describe the parallel channel to process color
Midget cells --> parvocellular and inter laminar regions --> layer 4C beta --> Layer 2,3 blobs --> thin stripe --> inferior occiptotemporal cortex
70
What are the ocular dominance columns?
Inputs from each eye terminate in different alternating bands of the cortex, approx 1mm wide
71
What are the orientation columns?
Vertical columns selectively respond to lines of a specific orientation
72
What are hyper columns?
A given region of 1mm2 will contain a complete sequence of both ocular dominance and orientation columns
73
Within the hyper column what are blobs sensitive to?
Color
74
Within the hyper column what are the inter blobs sensitive to?
Orientation
75
What is analyzed in the dorsolateral parieto-occipital cortex?
- "Where?"
- Analyzing motion & spatial relationship between object and between the body and visual stimuli
76
What is analyzed in the inferior occipitotemporal cortex?
- "What?"
- Analyzing form, with specific regions identifying colors, faces, letters and other visual stimuli
77
The dorsal pathway is in what cortex?
Parieto-occipital association cortex
78
What does the dorsal pathway analyze?
- "Where?" (analyze motion & spatial relationships)
- Between objects
- Between body & visual stimuli
- Combines visual, proprioceptive, vestibular & auditory info
79
What are the clinical implications of the dorsal pathway?
- Supplied by the MCA-PCA watershed territory
- Deficits in visual spatial analysis
- More common with non dominant hemisphere lesions
80
What cortex is the ventral pathway in?
Occipitotemporal association cortex
81
What is does the ventral pathway analyze?
- "What?"
- Form
- Color
- Faces
- Letters
82
What are the clinical implication of ventral pathway?
- Formed visual hallucinations
83
Where do formed visual hallucinations arise from?
Inferior temporo-occipital visual association cortex
84
What are the causes of formed visual hallucination?
- Toxic withdrawal
- Focal seizure
- Complex migraine
- Midbrain ischemia
- Psychiatric disorder
85
What is the blood supply to the ventral pathway?
PCA
86
Bilateral deficit to the ventral pathway can cause what?
- Prosopagnosia
- Achromatopsia
87
What is prosopagnosia?
Inability to recognize people by looking at their face (despite ability to describe features)
88
What is achromatopsia?
Central disorder of color perception
89
What is a scotoma?
Circumscribed region of visual loss
90
What can cause monocular scotoma?
Lesion to the retina
91
What causes monocular visual loss?
- lesion to optic nerve
- Glaucoma, optic neuritis, elevated ICP, tumor, trauma
92
What is monocular visual loss?
Visual loss from one whole eye
93
What causes bitemporal hemianopia?
Lesion to optic chiasm
94
What is bitemporal hemianopia?
Loss of vision of the temporal hemifields of each eye
95
What is optic neuritis a precursor to?
MS
96
What are the clinical features of optic neuritis?
- Eye pain (especially with eye movement)
- Monocular visual acuity
- Monocular central scotoma
- Decreased visual acuity
- Impaired color vision
- Complete loss of vision in one eye (severe)
97
What is a homonymous defect?
Visual field defect in the same region for both eyes
98
Homonymous defect can be caused by what?
Retrochiasmal lesions
- Optic tracts
- LGN
- Optic radiations
- Visual cortex
99
Lesions where cause contralateral homonymous hemianopia?
- Lesions of the optic tract, LGN or optic radiations
- Tumor, infarct, demyelination, hemorrhage, toxoplasmosis or infection
100
Lesions to where can cause contralateral superior quadrantanopia (pie in the sky)?
- Lesions to lower optic radiation - Meyer's Loop (Infarct, MCA inferior division, or lesion to temporal lobe)
- Lesion to the primary visual cortex below calcarine fissure (Infarct,PCA, or lesion to occipital lobe)
101
Lesions to where can cause contralateral quadrantanopia (Pie on the floor)?
- Lesions to superior optic radiations (Infarct, MCA inferior division, or lesion to the parietal lobe)
- Lesions to the primary visual cortex above the calcarine fissure (Infarcts, PCA, or lesion to the occipital lobe)
102
Lesions before the optic chiasm cause what deficit?
Monocular deficits
103
Lesion located at the optic chiasm cause what?
Bitemporal hemianopia (tunnel vision)
104
Lesions after the optic chiasm cause what?
Homonymous defects (the same region of visual field for both eyes)
105
Hemianopia is caused by lesions where?
All fibers on one side anywhere after the optic chaism contralateral to the visual field loss
106
Lesions to the pathway after the thalamus contralateral to the visual field loss cause what?
Quadrantanopia
107
In regards to quadrantanopia, inferior visual field loss is caused by damage to what?
superior radiation or visual cortex
108
In regards to quadrantanopia, superior visual field loss is caused by damage to what?
Inferior radiations or visual cortex
109
What is macular sparing?
Visual loss sparing the fovea
110
What are the possible causes of macular sparing?
- Chronically elevated ICP
- R PCA infarct sparing occipital pole
- Lesion to the inferior band of the R calcarine fissure preserving the occipital pole
111
What can cause monocular altitudinal scotoma?
Occlusion to either the upper or lower branch of the ophthalmic artery
112
What can cause binocular altitudinal scotoma?
- Bilateral occlusion of the PCA branches supplying the singular gyri
- Suggestive of vertebrobasilar insufficiency
113
What can syndrome of primary visual cortex cause?
Cortical blindness
- Loss of blink threat
- Loss of eye closure to bright light
- Loss of optokinetic nystagmus
- May have blindsight
114
What can syndrome of the inferior occipitotemporal cortex cause?
- Prosopagnosia (bilateral lesion)
- Achromatopsia
115
What can syndrome of the dorsolateral Parieto-Occipital cortex cause?
Balint's Syndrome (bilateral lesions)
116
What are some symptoms of Balint's Syndrome?
- Stimulantagnosia
- Optic ataxia
- Ocular apraxia
117
What is stimulantagnosia?
Impaired ability to see parts of visual stimuli as whole
118
What is optic ataxia?
Impaired ability to reach or point under visual guidanceW
119
