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Brain and Behavior Exam 2 > Lec 21 Eye Movements > Flashcards

Lec 21 Eye Movements Flashcards

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1
Q

What is the relationship between the pulling directions of extraocular eye muscles and the planes of semicircular canals?

A

same plane

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2
Q

What muscles are reponsible for horizontal eye movements?

A
  • only medial and lateral rectus
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3
Q

What muscles are responsible for vertical eye movement?

A

SR, IR, SO, IO

elevation = SR and IO
depression = IR and SO
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4
Q

What muscles control torsion when eye is abducted?

A

superior oblique = intorsion [top of eye toward nose]

inferior oblique = extorsion [top of eye away from nose]

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5
Q

What muscles control torsion when eye is adducted?

A

superior rectus controls intorsion [top of eye toward nose]

inferior rectus controls extorsion [top of eye away from nose]

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6
Q

Where are the oculomotor nuclei located?

A

in midbrain at level of superior colliculi

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7
Q

What does the oculomotor nerve innervate?

A
  • medial, superior, inferior recti
  • inferior oblique
  • levator palpebrae
  • caries parasympathetic from edinger-westphal nucleus to ciliary ganglion to innervate pupillary sphincter
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8
Q

What does the trochlear nerve innervate?

A

superior oblique

– nerve nuclei is contralateral to the eye it innervates

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9
Q

What does the abducens innervate?

A

lateral rectus

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10
Q

What are clinical signs when 3rd nerve function completely eliminated?

A
  • ptosis [lid is closed]
  • eye “down and out”
  • pupil dilated [mydriasis]
  • eye nonreactive to light
  • loss of accomodation
  • impaired elevation, depression, adduction [b/c weak medial rectus]
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11
Q

What is common cause of 3rd nerve palsy?

A
  • aneurysm of posterior communicating artery

- uncal herniation

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12
Q

What is emergency sign of impending brain herniation?

A
  • hutchinson pupil –> dilated non-reactive pupil caused by compression of 3rd nerve by herniation of temporal lobe uncus
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13
Q

Where are the paired trochlear nuclei located?

A
  • close to ventromedial edge of periaqueductal gray in midbrain
  • at level of inferior colliculi
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14
Q

What are signs of CN 4 dysfunction?

A
  • elevation of affected eye [hypertropia]
  • vertical diplopia [double vision]
  • may present with head tilt in direction of the affected eye
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15
Q

what is path of oculomotor nerve?

A
  • exits ventral in midbrain, passes between PCA/SCA through cavernous sinus to superior orbital fissure
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16
Q

what is path of CN4?

A

exits dorsally from midbrain and decussates

then through cavernous sinus to superior orbital fissure

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17
Q

What is the origin of CN4 dysfunction?

A
  • head trauma

- congenital defect

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18
Q

Where is abducens nuclei located?

A

lower pons / floor of 4th ventricle at facial genu/colliculus

19
Q

What is path of abducens nerve?

A

exits nucleus in pons, passes under gruber’s ligament

through cavernous sinus to superior orbital fissure

20
Q

What are signs of abducens nerve dysfunction?

A
  • medially directed eye [can’t adduct] on ipsilateral side

- deviation of eye toward one another [esotropia]

21
Q

Where is lesion likely to be if oculomotor, trochlear, and abducens all affected in one eye? how can you determine?

A
  • likely either orbital apex or cavernous sinus

if orbital apex –> optic nerve also affected so loss of vision

if cavernous –> no vision loss

22
Q

What is the medial longitudinal fasiculus? function?

A

MLF = bilateral fiber tract along cerebral aqueduct/ ventricle 4

  • used by interneurons of abducens 6 nucleus to synapse on contralateral medial rectus subnucleus of CN 3
  • facilitates conjugate horizontal eye movements [can coordinate simultaneous contraction of ipsilateral LR and contralateral MR]
23
Q

What two types of neurons are in the abducens nucleus?

A
  • lower motor neurons

- internuclear neurons

24
Q

What nerves does the part of MLF rostral to abducens nucleus interconnect?

A
  • vestibular nuclei

- nuclei of 3, 4, 6

25
Q

What happens if damage to MLF either in midbrain or pons?

A

internuclear ophthalmoplegia [INO]

26
Q

What are classic signs of a unilateral INO [internuclear opthalmoplegia]?

A

when try to turn gaze toward contralateral side

  • can’t adduct ipsilateral eye, nystagmus of contralateral abducting eye
  • preserved vergence: ipsilateral adducting during disconjugate movements
27
Q

What happens in lesions of abducens nerve or PPRF?

A

ipsilateral lateral gaze palsy
- imparied conjugate gaze in both eyes to the side of the lesion

ex. if lesion on left side
when try to turn gaze left –> nothing happens

28
Q

What do you see in lateral gaze palsy?

A

impaired conjugate gaze in both eye to the side of the lesion

29
Q

What can cause a lateral gaze palsy?

A
  • unilateral lesion of PPRF
30
Q

Where do eye movement command signals originate from?

A

UPMs in cortical eye fields primarily in frontal and parietal lobes then to:

–> anterior limb/genu of internal capsule

–> MLF

31
Q

What is sign of lesions [stroke] that destroys a cortical eye field?

A
  • ipsilateral gaze deviation [gaze preference]

= looks at the lesion

32
Q

What is saccade?

A

conjugate eye movement

  • rapid eye movement focusing fovea on stimuli
  • used to shift gaze

2 saccade gaze centers = PPRF + riMLF

33
Q

what is optokinetic nystagmus?

A
  • conjugate
  • back and forth beating eye movement
  • direction of nystagmus is always named for the quick phase [the quick reflexive glances in oppsoite direction from eye movement]
34
Q

what is vestibulo-ocular reflex?

A
  • eyes move in opposite direction of head rotation to maintain focus on target
35
Q

What is vergence?

A

disconjugate eye movement

- allows eyes to focus on near [convergence] or far [divergence] objects

36
Q

path of VOR action if head turns to left?

A

head turns to left –> endolymph in left horizontal canal shifts forward, activates canal nerve

  • -> projects to ipsilateral vestibular nucleus –> sends excitatory to contralateral abducens nucleus and [via MLF] ipsilateral oculomotor nucleus
  • -> inhibitory fibers from the vestibular nuclei project to ipsilateral abducens nucleus –> inhibition in ipsilateral LR and contra MR
37
Q

What is caloric testing?

A
  • test integrity of each horizontal canal

warm water into external auditory meatus –> mimicks head turn to ipsilateral side –> both eyes go toward contralateral ear then reset with nystagmus back toward ipsilateral [quick phase of nystagmus toward ipsilateral ear]

cold –> decreases nerve firing rate –> eyes move toward ipsilateral –> reset with nystagmus toward contralateral [quick phase of nystagmus toward contralateral ear]

COWS: cold opposite, warm same side

38
Q

What is smooth pursuit?

A

conjugate
- to maintain stable retinal image of moving target
velocity matches stimulus velocity

39
Q

Which eye muscle for down and in?

A

superior oblique

40
Q

What is unique about levator palpebrae superioris innervation?

A

bilateral supply rather than ipsilateral like all other eye muscles supplied by extraocular

41
Q

What is pathway for horizontal saccade?

A

cortical eye fields –> superior colliculus –> pprf –> ipsilateral avducens nucleus –> ipsilateral lateral rectus + contralateral media rectus [via MLF]

42
Q

What are the saccadic gaze centers?

A

pprf = paramedian pontine reticular formation for horizontal

riMLF = rostral interstitial nucleus of the MLF for vertical

43
Q

what is pathway for vertical saccade?

A

cortical eye fields –> superior colliculus –> riMLF –> motor neurons of CN 3 and r [SO/IO/SR/IR]

44
Q

What is the pathway for smooth pursuit?

A

descending project form cerebral cortex –> pontine nuclei –> cerebellum –> vestibular nuclei –> oculomotor nuclei

Brain and Behavior Exam 2 (21 decks)

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