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Brain and Behavior Exam 2 > Lec 25 Anatomy of Eye and Central Visual Pathways > Flashcards

Lec 25 Anatomy of Eye and Central Visual Pathways Flashcards

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1
Q

What is the path of innervation upstream to the PPRF?

A
  • from frontal eye field [FEF] projects through anterior limb of internal capsule and decussates [crosses] to opposite side at midbrain-pontine junction
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2
Q

Is the PPRF contra or ipsi from the medial rectus it innervates? what about the lateral rectus?

A 
medial = contra
lateral = ipsi
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3
Q

Which direction saccade does the right FEF command?

A

right FEF = left PPRF = commands conjugate gaze to the left = left lateral rectus and right medial rectus activated

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4
Q

What happens if there is a lesion of the abducens nerve [ex. left]?

A

CN VI palsy –> impaired abduction of ipsilateral eye

ex. if the lesion is on the left, the left eye will be turned in medially and unable to abduct

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5
Q

what happens if there is a lesion of the abducens nucleus or PPRF [ex. left]?

A

ipsilateral lateral gaze palsy
ex. if lesion on left, then when you try to look left nothing happens. when you look right you get normal right gaze

[left gaze would require action of left lateral rectus and right medial rectus. since PPRF upstream is out don’t have left lateral rectus function + don’t have the ], nothing happens
PPRF is

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6
Q

what happens if there is a lesion of the MLF [ex. left]?

A

interuclear opthalmoplegia [INO]
ex. if lesion of left MLF, when you try to look left its fine. when you try to look right –> right eye is fine but left eye stays [unable to look right/adduct], have nystagmus in right eye

convergence normal [can get ipsilateral [left] adduction in convergence just not in conjugate]

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7
Q

INO due to right MLF lesion can be seen when gaze toward which side?

A

gaze toward left [problem with right eye adduction]

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8
Q

What disease should you think of if you see INO [particularly bilateral younger pt vs older unilateral]?

A

bilateral younger = MS

unilateral older = stroke

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9
Q

What comprises the external eye?

A

sclera + cornea

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10
Q

what comprises the intermediate eye?

A

iris + ciliary body + choroid

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11
Q

what comprises the internal eye?

A

retina

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12
Q

What are the 2 most important structures for capturing light?

A

cornea, lens

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13
Q

What are zonule fibers?

A

connect lens to ciliary muscle

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14
Q

What are the 3 fluid compartments of the eye?

A

anterior chamber: filled with aqueous

posterior: where aqueous made by ciliary body

vitreous body: filled with vitreous humor

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15
Q

What are the photoreceptors in the retina?

A

rods and cones

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16
Q

What are horizontal cells in the retina?

A

spread laterally between photoreceptor and bipolar layer, spread transmission laterally

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17
Q

what are amarcine cells in the retina?

A

spread laterally between bipolar layer and ganglion cells, spread transmission laterally

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18
Q

What is horner’s syndrome? possible dangerous cause?

A

sympathetic disorder –> could indicate dissection of cartoid artery

signs: ptosis, anhidrosis [decreased sweating], miosis

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19
Q

What is tonic pupil? cause?

A

dissociation of light-near reflexes cause by lesion in ciliary ganglion

signs: mydriasis [dilation], absent pupillary light reflex, preserved pupillary near reflex [but slow to return to dilate]

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20
Q

What is argyll-robertson pupil? cause?

A

dissociation of light-near reflexes caused by tertiary neurosyphilis or diabetes

  • irregular pupils accomodate but don’t react = constrict in near reflex but not in light
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21
Q

What is marcus gunn pupil?

A
  • due to optic neuropathy or severe retinal injury

decreased bilateral pupil constriction when light is shone in affected eye relative to unaffected –> look for paradoxical pupil dilation in bad eye after constriction

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22
Q

What is the order of cells in the retina from outside to in [same direction light travels]?

A

ganglion cells –> amacrine cells –> bipolar cells –> horizontal cells –> photoreceptors

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23
Q

What is contained in “nuclear” layers in retina? what about “plexiform” layers?

A

nuclear layers have cell bodies

plexiform layers have synapses

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24
Q

What layer of retina has ganglion cell axons?

A

nerve fiber layer

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25
Q

What is function of pigment epithelium layer of retina?

A

contains melanin, absorbs light + prevents back scatter, phagocytosis of discarded outer segments

26
Q

What is function of rods [type of spatial resolution, light sensitivity, vision]?

A
  • low spatial resolution
  • high light sensitivity
  • can detect single photon, night vision, peripheral vision
27
Q

What is function of cones [type of spatial resolution, light sensitivity, vision]?

A
  • high spatial resolution
  • low light sensitivity
  • acuity and color
  • day vision
  • central foveal vision
28
Q

what is degree of convergence photoreceptors and their bipolar cells onto retinal ganglion for cones vs rods?

A

many rods onto few bipolar cells = high degree of convergence to detect single photon

less convergence for cones = for high visual acuity to retain spacial specificity

29
Q

What is the fovea?

A

region of retina sensitive to acuity. has fewer cells per layer, cones only [ no rods]

30
Q

What covers the retina?

A

covered by dura because it is a CNS structure

31
Q

What is the macula?

A

area around the fovea, responsible for central vision

32
Q

What parts are retina are responsible for peripheral vs central portion of right visual field?

A 
central = left temporal retina
peripheral = right nasal retina
33
Q

Retro-chiasmally [before chiasm toward brain] what info is carried in the right optic tract?

A

all info from left visual field

34
Q

What crosses in the optic chiasm?

A

only the nasal halves of the retina that are then responsible for ipsilateral peripheral vision [ipsilateral meaning in regard to side after chiasm and eye visual field]

35
Q

Info from the inferior nasal visual field is mapped to what part of the retina?

A

superior temporal part of retina

36
Q

What makes optic chiasm particularly vulnerable?

A

sits just next to anterior communicating artery –> vulnerable to aneurysms

right near pituitary –> pituitary may jam up into optic chiasm

37
Q

What is the convention for how visual fields are drawn?

A
  • visual fields drawn the way a person sees the world –> visual field of left eye shown on left and that of right eye on the right
38
Q

What myelinates the retina?

A

oligodendrocytes [not schwann cells] because its part of CNS

39
Q

What is the magnocellular pathway [type of info it carries, from which photoreceptors, size of receptive field]?

A
  • one of two main functional channels of vision
  • carries rod-generated signals of motion/direction
  • insensitive to color + detail
  • large receptive fields
  • mostly from peripheral retina
40
Q

what is the parvocellular pathway [type of info it carries, from which photoreceptors, size of receptive field]?

A
  • one of two main functional channels of vision
  • carries cone-generated signals
  • small receptive fields
  • acuity and color sensitive
41
Q

Where do most optic tract fibers terminate?

A

lateral geniculate nucleus [LGN] of thalamus

42
Q

Which layers do magnocellular vs parvocellular go in the LGN?

A

layers 1-2 = magnocellular

layers 3-6 = parvocellular

43
Q

which layers of LGN from ipsilateral vs contralateral retina?

A 
contralateral = 1, 4, 6
ipsilateral = 2, 3, 5
44
Q

Where is the primary visual cortex?

A

in occipital lobe in calcarine fissure

45
Q

Fibers from which part of visual field travel through temporal lobe radiation vs temporal lobe radiation [meyer’s loop]?

A

superior visual field [inferior retinal quadrant] = temporal

inferior visual field [superior retinal quadrant] = parietal

46
Q

What is effect of lesion to optic tract or LGN [ex. left]?

A

homonymous heminaopia in contralateral visual field

if left optic tract/LGN –> right half of visual field for both eyes is impaired

47
Q

What does homonymous hemianopia mean?

A

loss of half of visual field for each eye. ex. if its a left homonymous hemianopia –> the left half of visual field for each eye is impaired

48
Q

What is common cause of optic tract homonymous hemianopia?

A
  • occlusion of PCA or anterior choroidal artery

- causes lesion of optic tract or LGN lesion

49
Q

What is effect of meyer’s loop lesion [ex. right side]?

A
  • contralateral homonymous superior quadrant hemianopia
  • meyer’s loop carries superior visual field –> get “pie in the sky” = quadrant of superior visual field impaired

ex. right side loop lesion –> loss of superior left quadrant visual field for both eyes

50
Q

What is effect of lesion of parietal optic radiation [ex. right side]?

A

contralateral homonymous inferior quadrant hemianopia

ex. right side lesion –> loss of inferior left quadrant visual field for both eyes

51
Q

Where does superior vs inferior visual field map to in calcarine fissure?

A

superior field –> inferior calcarine fissure

inferior field –> superior calcarine fissure

52
Q

where does peripheral visual field vs macular part map to in calcarine fissure?

A 
peripheral = more anterior
central/macular = more posterior toward occipital pole
53
Q

What is effect of lesion at optic chiasm?

A

bitemporal hemianopia –> peripheral vision lost in both sides because the nasal part of retina is what crosses = the temporal part of visual field

54
Q

What is effect of lesion of primary visual cortex?

A
  • homonymous hemianopia of contralateral side

- usually some central vision spared [macular sparing]

55
Q

What causes macular sparing in primary visual cortex lesion?

A
  • large extent of macular projection onto calcarine cortex

- dual blood supply from MCA and PCA

56
Q

Which is dorsal vs ventral of what/where path? what fasciculi respectively?

A 
what = dorsal = inferior longitudinal fascilucus, terminates in inferior temporal cortex
where = ventral = superior longitudinal fasciculus, terminates in posterior parietal cortex
57
Q

Where do fibers of pupillary light reflex path terminate?

A

midbrain pretectum –> ipsilateral and contralateral edinger-westphal nuclei [contralateral via posterior commissure

58
Q

What is the pupillary near reflex?

A

pupils constrict when shift gaze from distant to near

59
Q

What are the steps along the direct pupillary light reflex?

A

light to eye –> optic nerve –> chiasm –> tract –> midbrain pretectum
–> ipsilateral edinger westphal –> CN 3 to ciliary ganglion –> ipsilateral sphincter muscle contracts / pupil constricts

60
Q

What are the steps along the consensual light reflex?

A

light to eye –> optice nerve/chiasm/tract –> midbrain pretectum
–> posterior commissure –> contralateral edinger westphal –> cn 3 to ciliary ganglion –> contralateral sphincter contracts /pupil constricts

61
Q

What are ligh-sensitive biological clocks?

A
  • photosensitive retinal ganglion cells transduce light energy and convert to electrical impulse
  • non-image forming cells but tell you ambient light intesity
    allow for:
  • synchronization circadian rhythms to light/dark cycle via hypothalamus
  • help regulate pupil diameter via pretectal nucleus
  • participated in light-dependent release of melatonin from pineal gland

Brain and Behavior Exam 2 (21 decks)

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