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Neuro Exam 3 > Visual Tracts > Flashcards

Visual Tracts Flashcards

1
Q
  • What are the components of the visual pathway
A
  • Axons of ganglion cells and the axons of higher order cells on which they synapse
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2
Q
  • Visual pathway has what type of fiber arrangement?
  • Is this maintained throughout the pathway?
A
  • Retinotopic
  • Yes
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3
Q
  • Define visual field
A
  • Area person sees when both eyes are fixed in a certain position
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4
Q
  • Define retinal field
A
  • Light from visual field that travels through pupil and creates an image on the retina (what the retina sees)
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5
Q
  • The object of attention is focused on what anatomical structures?
  • What lies just medial to these structures?
A
  • Fovea centralis and macula lutea
  • Just medial to the macula is the optic disc, which forms our blind spot (no photoreceptors in this region, because this is where retinal axons are leaving the eye as the optic nerve)
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6
Q
  • What are the zones of visual fields? What type of information do they contain?
A
  • Binocular zone
    • ​Broad central region seen by both eyes
  • Monocular zone (R/L)
    • ​Seen only by one eye (hence the name)
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7
Q
  • Retinal field
  • Visual fields are divided into _
  • Each of these are divided into _
A
  • Retinal fields (location on retina that object in visual field is projected)
  • Each visual field-divided into retinal hemifields (Nasal-medial and temporal- lateral halves of a retina)
  • Each hemifield divided into upper and lower quadrants
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8
Q
  • Are visual system lesions described in terms of retinal or visual fields?
A
  • Visual
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9
Q
  • The left half of a visual field forms an image on the _ half of the left retina and the _ half of the right retina
  • The right half of the visual field forms an image on the _ half of the left retina and _ half of the right retina
A
  • Left half of a visual image
    • Nasal half of left retina
    • Temporal half of right retina
  • Right half of a visual image
    • Nasal half of right retina
    • Temporal half of left retina
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10
Q
  • Where do the two optic nerves partially decussate?
  • How do they decussate?
A
  • Optic chiasm
  • Nasal half of each retina-projects to contralateral optic tract
  • Temporal half of each retina-ipsilateral optic tract
  • This helps with depth perception
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11
Q
  • What forms the optic tract?
A
  • FIbers from temporal retina of ipsilateral eye
  • Fibers from nasal retina of contralateral eye
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12
Q
  • Where does the optic tract terminate?
  • How many layers does this nucleus have?
  • How do they terminate?
  • Ventral base of this nucleus formed by _
  • Dorsal and lateral bases of this nucleus formed by _
A
  • LGN of the thalamus
  • 6
  • Retinotopically
  • Ventral base-fibers from incoming optic tract (retinogeniculate fibers)
  • Dorsal and lateral bases of LGN-outgoing optic radiations
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13
Q
  • Magnocellular (M) layers of LGN
A
  • Layers 1 and 2 (Ventral)
  • Contain large cells
  • Receive inputs relaying from rods (larger receptive fields and thick and fast axons)
  • Sensitive to moving stimuli
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14
Q
  • Parvocellular (P) Layers of LGN
A
  • Layers 3-6 (Dorsal)
  • Small cells
  • Inputs from cones
  • Small receptive fields and slower conducting . axons sensitive to STATIONARY stimuli (high acuity color vision)
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15
Q
  • Where do ganglion cell axons from temporal axon go in the LGN of the thalamus?
A
  • Remember that temporal retina ganglion cells stay ipsilateral
  • Project to IPSILATERAL LGN (Layers 2,3,5)

Example (looking at right visual field)

-Left temporal: projects to left LGN (2,3 and 5)

Example (looking at left visual field)

-Right temporal: projects to right LGN (2,3 and 5)

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16
Q
  • Where do ganglion cell axons from nasal retina terminate in the LGN?
A
  • Nasal fibers cross
  • so will terminate in CONTRALATERAL LGN (Specifically 1,4 and 6)

Example (looking at right visual field)

-Right nasal fibers-layers 1,4 and 6 of left LGN

Example (looking at left visual field)

-Left nasal fibers-layers 1, 4 and 6 of LGN

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17
Q

What are optic radiations?

What is another name for this pathway?

A

Secondary neurons from LGN that are relaying information to the primary visual cortex (striate cortex) [on upper and lower banks of calcarine sulcus]

Genticulostriate/genticulocalcarine

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18
Q
  • How are optic radiations divided?
A
  • Fibers from lower quadrant of contralateral hemifields target superior bank of calcarine sulcus/cuneus
  • Fibers from upper quadrant of contralateral hemifields target inferior bank of calcarine sulcus/lingual gyrus
  • Fibers conveying information from macula and fovea originate from central regions of LGN and pass to caudal visual cortex
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19
Q

Temporal damage can lead to a _ visual field deficit

A
  • Superior (Meyer’s loop)
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20
Q
  • How is the macula represented in the LGN/Visual Cortex?
A
  • Disproportionately large volumes relative to its size
  • Represented on posterior aspect of occipital lobe
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21
Q
  • VIsual field is comprised of four _
  • Each projects to its own quadrant of the primary visual cortex
  • _ and _ inversion in projection of visual field on the visualcortex
A
  • Quadrants
  • Lateral and vertical inversion
22
Q
  • Summary of retinotopic organizaton
23
Q
  • Primary visual cortex
    • Broadmans area _
    • Macula represented more _
    • Peripheral areas represented more _
    • Alsi called _ cortex
A
  • 17
  • Posteriorly
  • Anteriorly
  • Striate (numerous myelinated fibers within layers give it a striped appearance)
24
Q
  • Visual association cortex
    • Broadman area _ and _
    • Grouped with other parts of the temporal and parietal lobes to form the _ cortex
    • LGN also targets this area to interpret what type of information?
A
  • 18 and 19
  • VIsual association/Extrastriate cortex
  • (Parieto-occipito-temporal area)
  • Location
  • Motion
  • Form
  • Color
25
Q

Other visual cortical areas and their functions

A
  • Superior colliculus
    • Directing eye movements
  • Pretectal/pretectum area
    • Pupillary light reflex
26
Q
  • Pupillary innervation for Pupillary Constriction
  • Pupillary innervation for pupillary dilation
A
  • Parasympathetic postganglionics (Edinger Westphal nucleus) to pupillary contrictor m
  • Sympathetic postganglionic fibers (Superior Cervical ganglion) to pupillary dilator m.
27
Q
  • Describe the pupillary constriction reflex
A
  1. Retinal axons terminate in olivary pretectal nucleus (pretectum)
  2. B/L projections sent to Edinger Westphal preganglionic nucleus (contralateral tracel via posterior commissure)
  3. Parasympathetics exit with CN III and synapse on IPSILATERAL ciliary ganglion
  4. Postganglionic fibers (short ciliary nerves) excite pupillary constrictor m.
28
Q
  • Decussation of retinal fibers permits _ response in opposite eye
A
  • Consensual
29
Q
  • Lesions of the pupillary reflex pathway:
    • Optic nerve partially damaged?
    • What happens?
A
  • Shining light into that eye will produced diminished direct and consensual responses
  • Both reflexes when light is shone into opposite eye will be fine
30
Q
  • Lesions of the pupillary reflex pathway:
    • ​Toatl lesion at optic chiasm
    • Symptoms?
A
  • Blind eye (neither direct or consensual response when eye is illuminated)
31
Q
  • Lesions of the pupillary reflex pathway
    • ​Lesion in optic tract/pretectum
    • Symptoms?
A
  • Neither response is lost
  • Reflexes may be weaker
32
Q
  • Lesions of pupillary reflex patheway
    • ​Large lesion in posterior/dorsal midbrain
    • Symptoms?
A
  • Weakening of pupillary responses b/l
33
Q
  • Lesions of pupillary reflex pathway
    • ​Lesion in oculomotor nucleus or nerve
    • Symptoms?
A
  • Direct and consensual reflexes will be lost ipsilaterally (same side of lesion)
  • Contralateral side is fine
34
Q
  • Hemianopia
A
  • Blindness in one half of the visual field
35
Q
  • Quadrantanopia
A
  • Blindness in a quadrant of the visual field
36
Q
  • Homonymous visual fields
A
  • Visual field loss areas are similar in both eyes
37
Q
  • Heteronymopus visual fields
A
  • Visual field losses in either eye do not overlap
38
Q
  • Macular sparing
A
  • Can still see center of visual field
  • Can’t see periphery of visual field
39
Q

Congruous visual defect

A
  • Visual field loss of one eye can be superimposed on that of the other eye
  • The closer a lesion is to the visual cortex, the more likely a congrous visual defect will be present
40
Q
  • Damage anterior to chiasm affects _ ye
  • Damage @ optic chiasm causes _ deficits
  • Damage behind optic chiasm causes _ deficits
A
  • Ipsilateral
  • Heteronymous
  • Homonymous
41
Q
  • What will the deficit be if area 1 is damaged?
A
  • Complete blindness in right eye
  • Left eye will be fine
42
Q
  • What will the deficit be if area 2 is lesioned?
A

Bitemporal hemianopia

43
Q
  • What will the deficit be if area 3 is damaged?
A
  • Left hemianopia in right eye
44
Q
  • What will the deficit be if area 4 is damaged?
A
  • Left homonymous quadrantinopia
45
Q
  • What will the deficit be if area 5 is damaged?
A
  • Left superior quadrantinopia
46
Q
  • What will the deficit be if area 6 is damaged?
A
  • Left homonymous hemianopia
47
Q
  • What will the deficit be if area 7 is damaged?
A
  • Left inferior quadrantanopia
48
Q
  • What will the deficit be if area 8 is damaged?
A
  • Left superior quadrantanopia
49
Q
  • Associative visual agnosia
A
  • Infarction of left occipital lobe and posterior corpus callosum
  • D/t occlusion of PCA
  • Disconnects language area from visual association cortex
  • Patient cannot name or describe an object but can recognize and demonstrate its use
    • ​Visual perception is intact
    • Alexic and agraphia may be present
50
Q
  • Good summary slide of visual deficits and where lesions occur

Neuro Exam 3 (14 decks)

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