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Neuro Block 6 > Oculomotor System > Flashcards

Oculomotor System Flashcards

1
Q

Maintaining fixation of eyes on a target

A

Foveation

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2
Q

Point to point shift of fiaxation

A

Saccade

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3
Q

Continuous conjugate eye movements

A

Smooth pursuit

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4
Q

Eyes move opposite to head movement, maintains fixation on a target. Tests brainstem and cerebrum

A

Vestibular-ocular reflex movements

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5
Q

Visual system guides smooth pursuit and fast reflexive re-centering of eyes

A

Optokinetic reflex

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6
Q

Fast re-centered of eyes during/after slow eye movement

A

Nystagmus

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7
Q

Fovea is at the back of the eye, lateral (temporal) to the optic disc

A

Visual axis

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8
Q
  • parallel to the optic nerve

- the 4 rectus muscles are attached at the common tendon, aka Annulus of Zinn.

A

Orbital axis

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9
Q

Vectors for hthe 4 rectus muscle actions are defined by what

A

A line between the common tendon and the point of attachment to the eye

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10
Q

What is the only CN to exit the back of the midbrain

A

Trochlear

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11
Q

What does the trochlear nerve do as it exits the midbrain

A

Cross-crosses each other within midbrain as they exit

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12
Q

Total lesion of CN III

A

Results in Down and out sign in ipsilateral eye. Depressed and abducted due to unopposed actions. Intact functions of IV and VI nerves

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13
Q

3rd nerve palsy results in

A
  • Diplopia due to dysconjugate eye positions
  • drooping or total closure of eyelid
  • pupil dilation and loss of direct response
  • loss of accommodation
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14
Q

Signs of trochlear palsy

A
  • hypertropia and mild extortion
  • vertical diplopia
  • compensate by tilting head diagonllay down
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15
Q

Right abducens palsy

A
  • medial strabismus of right eye due to unopposed MR
  • between when viewing closer objects, worse when looking at far
  • dysconjugate eyes (diplopia) when looking toward affected side
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16
Q

For horizontal gaze

A

The VI nucleus drives activation in the contralateral III nucleus

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17
Q

Function of the VI nucleus

A

When one VI nucleus is going to abduct the ipsilateral eye, it activates contralateral III nucleus and medial rectus

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18
Q

VI nucleus projects to contralateral CNIII nucleus by sending axons across the midline, then sending up the

A

Medial longitudinal fasciculus (MLF)

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19
Q

When is the CNIII/VI nucleus activation recruited?

A

During both voluntary horizontal gaze and by reflex horizontal gaze

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20
Q

Left motor cortex and the circuitry for horizontal gaze

A

Crosses midline in pons to right PPRF, activates right VI nucleus

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21
Q

Right motor cortex and the circuitry for horizontal gaze

A

Projects down and croasses midline in pons to left PPRF, activates left VI nucleus

22
Q

What area is important for vision and just anteiror to precentral gyrus

A

Frontal eye fields: contralteral saccades

23
Q

What area of the cerebrum is important for spatial aspects to vision

A

Parietal occipito temporal area

24
Q

What is an important part of the cerebrum in the back for vision

A

Visual cortex

25
Q

Right abducens nerve damage

A
  • normal left gaze
  • Right LR rectus palsy
  • right eye fails to look right
26
Q

Right abducens nucleus damage

A
  • normal left
  • in right gaze, neither eye looks right
  • right CN 6 nucleus damaged
  • right CN 6 nucleus fails to activate left CN 3 nucleus
27
Q

Right PPRF nucleus damage

A
  • left is normal
  • similar to 6th nucleus damage
  • height eye looks right
  • right CN6 nucleus not activated
  • right CN 6 nucleus fails to activate left CN 3 nucleus, so left MR not activated
28
Q

Damage to left MLF

A
  • left gaze normal
  • for right gaze, connection from right CN 6 nucleus to left CN 3 nucleus is damaged
  • right LR can abduct
  • right CN 3 nucleus not activated
  • right MR not activated
29
Q

Damage to left CN 6 nucleus and bilateral MLF damage (1.5 syndrome)

A

Left gaze

  • left CN 6 nucleus damaged
  • left LR fails to abduct
  • right CN3 nucleus not activated by damaged left CN 6 nucleus
  • left MR not activated
  • neither eyes look left

Right gaze
-right CN 6 nucleus cannot activate left CN 3 nucleus, so left MR not activated

30
Q

What does head turn do to gaze?

A

Causes conjugate horizontal gaze opposite direction

31
Q

Vestibular nuclei in the medulla project where

A

To contralateral PPRF and activate contralateral CN 6 nucleus

32
Q

What does leftward head turn activate

A

Left horizontal semicircular canal

33
Q

What does the left vestibular nucleus activate

A

Right PPRF and right CN 6 nucleus

34
Q

What does the right CN 6 nucleus do once the left vestibular nucleus activates it

A
  • activates right LR and abducts the right eye

- projects up left MLF to activate the left CN3 nucleus and left MR (conjugate gaze to left)

35
Q

What can the vestibulo-ocular reflex be used for

A

To evaluate the brainstem (medulla, pons, midbrain) in an unconscious unresponsivene patient

36
Q

In a patient with conjugate gaze palsy, the vestibulocochlear-ocular reflex testing can be used for what

A

Testing the integrity of the CN 6 lower motor neurons

37
Q

What does a normal vestibuli-ocular reflex suggest in someone with a conjugate gaze palsy

A

-conjugate gaze palsy is the result of an UMN lesion (central hemisphere lesion instead of brainstem)

38
Q

How do you test the vestibulo-ocular reflex?

A

Dolls head maneuver

39
Q

What is the caloric test?

A

Putting warm or cold water in ear while patient lies supine. Warm water activates the canals on that side, cold water inhibits the canals on that side

40
Q

Putting warm water in ear for caloric test

A
  • activates the horizontal canals on that side
  • activates CN 6 nucleus
  • slow eye movement to the right, then nystagmus to the left.
41
Q

Cold water in the ear with the caloric test

A
  • inhibits the horizontal canals on that side, activates canals on the opposite side
  • inhibits vestibular activation of left CN6 nucleus, meanwhile CN 8 activates right CN6 nucleus
  • conjugate slow movement to same side
  • nystagmus beats to opposite side of cold water
42
Q

What direction does nystagmus beat when warm water is added?

A

To same side as ear receiving warm water

43
Q

What side does the nystagmus beat to when cold water is added to the ear?

A

Opposite side of cold water

44
Q

Nystagmus and optokinetic reflex

A

Eyes first slow-pursuit to the right, then last to left.

Whatever direction the object is moving, the nystagmus beats in the opposite direction

45
Q

The nystagmus phase of the vestibulocochlear-ocular reflex in response to doll head to caloric testing is dependent on what

A

Cerebrum

46
Q

What will happen in the VOR with an unconscious patient with a cerebral pathology?

A

The slow phase response will be present but the nystagmus phase will be absent, thus the COWS mnemonic does not apply

47
Q

In VOR, if neither the slow phase nor the nystagmus is seen, then a ______ lesion is more likely

A

Brainstem

48
Q

What is voluntary vertical gaze driven by

A

Cerebral cortex activation of III and IV nuclei (III for elevation, III and IV for depression)

49
Q

Other than cerebral cortex activation of III and IV nuclei, what else can also drive vertical gaze?

A

Vertically-oriented semicircular canals and otolith organs. They talk to III and IV nuclei to move eyes vertically

50
Q

What are the middle man regions of the vertical gazes

A
  1. The rostral interstitial nucleus of the MLF

2. The superior colliculi

Neuro Block 6 (8 decks)

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