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Neuro Test 3 > visual tracts > Flashcards

visual tracts Flashcards

1
Q

visual system

A

formation of a light image (photons) by the phoreceptive retina
-info transduced by rods and cones —-> ganglion cells –> higher order cells –> thalamus –> visual pathway

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2
Q

retinotopic

A

arrangement of fibers that is maintained at each relay location
-small regions of the retina are represented in specific regions centrally

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3
Q

visual fields

A

area that a person is able to see when both eyes are fixed in one position

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4
Q

retinal field

A

light passes from objects in the visual field through the pupil to subtend an image upon the retina

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5
Q

fovea centralis and macula lutea

A

location where the object of attention is focused and centered in the retinal field

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6
Q

optic disc

A

medial to the macula

  • region where retinal axons leave the eye as the optic nerve
  • no photoreceptors –> blind spot
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7
Q

visual field zones

A
  • binocular zone

- monocular zone (R/L)

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8
Q

binocular zone

A

broad central region seen by both eyes

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9
Q

monocular zone

A

seen only by the corresponding eye

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10
Q

retinal hemifields

A

nasal and temporal halves

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11
Q

quadrants

A

each hemifield is divided into upper and lower parts

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12
Q

visual system lesions are described in terms of their ____

A

visual deficits

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13
Q

What way is the image formed on the retina inverted?

A

both lateral and vertical dimensions

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14
Q

decussation of CN II

A

two optic nerves partially decussate in the optic chiasm

  • nasal half of each retins –> contralateral optic tract
  • temporal half of each retina –> ipsilateral optic tract
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15
Q

optic tract

A

fibers from temporal retina (ipsilateral eye) + fibers from nasal retina (contralateral eye)

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16
Q

depth perception

A

higher order function that needs to bring together info from comparable areas of both retinas

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17
Q

Where does the optic tract terminate?

A

lateral geniculate nucleus of the thalamus

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18
Q

lateral geniculate nucleus (LGN)

A

thalamus

  • six layers with myelinated fibers sandwiched between them
  • fibers terminate in a precise retinotopic pattern
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19
Q

optic tract (retinogeniculate) fibers

A

ventral base of lateral geniculate nucleus

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20
Q

optic radiations

A

dorsal and lateral borders of lateral geniculate nucleus

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21
Q

layers of the LGN

A

1-6

  • magnocellular
  • parvocellular
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22
Q

magnocellular (M) layers

A

1-2 ventral

  • large cells
  • ganglion cell inputs relaying from rods –> larger receptive fields and thick, rapidly conducting axons, sensitive to moving stimuli
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23
Q

parvocellular (P) layers

A

3-6 dorsal

  • small cells
  • ganglion cell inputs relaying from cones –> small receptive fields, slower conducting axons, tonically responsive to stationary stimuli, high-acuity color vision
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24
Q

temporal retina

A

remain uncrossed and terminate in layers 2, 3, 5 of ipsilateral LGN

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25
Q

nasal retina

A

cross and terminate in layers 1, 4, 6 of contralateral LGN

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26
Q

how many times is the same point represented in the LGN?

A

6 times
same medial-lateral position in layers 1-6 of LGN
layers 2, 3, 5 from ipsilateral temporal retina
layers 1, 4, 6 from contralateral nasal retina

27
Q

optic radiation

A

secondary neurons from LGN extend a large bundle of myelinated fibers
-retinotopic organization maintained, but individual fibers carry info from one eye
-relay to primary visual cortex (striate cortex)
AKA geniculostriate or geniculocalcarine pathway

28
Q

primary visual cortex

A

input from LGN optic radiation

-upper and lower banks of the calcarine sulcus

29
Q

Where do fibers from the lower quadrant of the contralateral hemifields

  • originate
  • arch
  • target
A
  • originate from dorsomedial LGN
  • arch caudally to pass retrolenticular limb of the internal capsule
  • target superior bank of calcarine sulcus on the cuneus
30
Q

Where do fibers from the upper quadrant of the contralateral hemifields

  • originate
  • arch
  • target
A
  • originate from the ventrolateral portion of the LGN
  • do not pass directly caudal to the visual cortex
  • arch rostrally passing into white matter of the temporal lobe to form a broad U-turn: Meyer loop
  • target inferior bank of the calcarine sulcus on the lingual gyrus
31
Q

Where to fibers conveying info from the macula and fovea

  • originate
  • target
A
  • originate from central region of the LGN

- target caudal portions of the visual cortex

32
Q

What can temporal lobe damage deficit?

A

superior visual field - Meyer’s loop

33
Q

macula is represented by disproportionately ____ volumes relative to size of the LGN and visual cortex

A

large

34
Q

Where is the macula represented in the occipital lobe?

A

occipital pole

35
Q

What Brodmann’s area is the primary visual cortex?

A

17 - above and below the calcarine sulcus

  • inferior fields above sulcus
  • superior fields below sulcus
  • macula posteriorly
36
Q

visual association cortex

A

Brodmann’s areas 18-19 (rest of occipital lobe)
AKA extrastriate cortex
-parieto-occipito-temporal area
-heavily interconnected with 17
-LGN also sends targets - helps interpret location, motion, form, color

37
Q

superior colliculus - visual cortical area

A

spatially directs head movements and visual reflexes

  • retinal input: select fibers that bypass LGN, pass over MGN in the brachium of the superior colliculus, terminate retinotopically in the superior colliculus
  • cortical input: area 17 via brachium, pattern coincides with retinotopic map
  • spinotectal (somatosensory) and auditory inputs

DIRECTING EYE MOVEMENT

38
Q

pretectal/pretectum area

A

bilateral group of interconnected nuclei near midbrain/forebrain junction

  • inputs: afferent bilateral fibers from optic tract, LGN, and suprachiasmatic nucleus
  • pretectal nuclei respond to varying intensities of illuminance
  • mediate non-conscious behavioral responses to acute changes in light

PUPILLARY LIGHT REFLEX

39
Q

pupillary light reflex

A 
sympathetic postganglionic fibers (superior cervical ganglion) --> pupillary dilator m
parasympathetic postganglionics (Edinger-Westphal nucleus) --> pupillary constrictor m
40
Q

pupillary constriction

A

visceral motor efferents of CN III arise in Edinger-Westphal preganglionic nucleus

  • preganglionic fibers terminate in ciliary ganglion and axons of postganglionic cells innervate: constrictor pupillae m of the iris and ciliary m
  • cholinergic, preganglionic motor neurons travel with the ipsilateral oculomotor N and synapse in the ciliary ganglion
  • cholinergic, postganglionic motor neurons send axons via the short ciliary nerve to supply ciliary m and pupillary constrictor
41
Q

4 neuron arc of pupillary reflex

A
  1. retinal axons terminate in olivary pretectal nucleus (pretectum)
  2. bilateral projections to Edinger-Westphal preganglionic nucleus (contralateral travel with posterior commissure)
  3. parasympathetics exit w/ CN III synapse in ipsilateral ciliary ganglion
  4. postganglionic fibers (short ciliary nerves) excite pupillary constrictor m
42
Q

What permits consensual response of pupillary constriction in opposite eye?

A

decussation of retinal fibers

43
Q

What does the pupillary light reflex test?

A

CN III and brainstem function

lesion: loss of direct or consensual pupillary response or in uneven pupil size

44
Q

anisocoria

A

uneven pupil size

45
Q

What is a grave sign in an unconscious person?

A

dilated, unresponsive (fixed) pupils

46
Q

What happens if CN III is lesioned?

A

loss of preganglionic fibers result in ipsilateral mydriasis (dilation of pupil) and paralyisis of accomodation

47
Q

What happens if short ciliary nerves are damaged?

A

tonic dilated pupil

48
Q

optic N partially damaged

A

shining light into damaged eye will produced diminished direct and consensual responses, but both will be present when the undamaged eye is illuminated

49
Q

total lesion of optic N

A

blind eye, will not induce direct nor consensual response when eye is illuminated

50
Q

lesion of optic tract or pretectum

A

neither direct or consensual response is lost, although reflexes may be weaker

51
Q

large lesion in posterior (dorsal) midbrain

A

weaken pupillary responses bilaterally

52
Q

lesion in oculomotor nucleus or nerve

A

both direct and consensual responses lost ipsilaterally, but will be present contralaterally

53
Q

hemianopia

A

blindness (-anopia or -anopsia) in 1/2 of the visual field

54
Q

quadrantanopia

A

blindness of a quadrant of a visual field

55
Q

homonymous visual fields

A

conditions in visual field losses are similar in both eyes

56
Q

heteronymous visual fields

A

conditions in which the two eyes have non-overlapping field losses

57
Q

macular sparing

A

visual field loss that preserves vision in the center of the visual field

58
Q

conguous

A

visual field loss of one eye can be superimposed on that of the other eye (symmetrical)
-more likely closer to visual cortex

59
Q

inconguous

A

not symmetric

-more anterior lesion of optic tract or radiations

60
Q

damage anterior to the chiasm affects

A

only the ipsilateral eye

61
Q

damage at the chiasm causes

A

heteronymous deficits

62
Q

damage behind chiasm causes

A

homonymous deficits

63
Q

associative visual agnosia

A
  • infarction of the left occipital lobe and posterior corpus callosum
  • typically due to secondary occlusion of the posterior cerebral artery
  • disconnects the language area from the visual association cortex
  • pt cannot name or describe an object in the visual field, but he can recognize and demonstrate its use
  • visual perception intact
  • may be alexic (unable to read) and writing abiliaty may be affected agraphia

Neuro Test 3 (11 decks)

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