L26: Oculomotor & Motor learning Flashcards

1
Q

Is frontal eye field tonically active?

A

Yes

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2
Q

Saccades are really fast eye movements. What do saccade generators need? Where will we find the vertical saccade generator? What about the horizontal saccade generator?

A

Saccade generator needs new firing rate & burst of activity to create saccades. So there’s a burst that will be integrated over time to create firing rate. Therefore, there’s an integrator in the saccade generator.

Vertical saccade generator = midbrain
Horizontal saccade generator = pons

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3
Q

What are some symptoms associated with Abnormal Frontal Eye Fields?

*forebrain disorder

A

-can’t make saccade movements
if the left frontal eye field is damaged –> can’t make saccade movements to right

-preserved pursuit movements
when pt above with the damaged left frontal eye field is asked to track object to his right with his eyes, he can b/c nothing is wrong with the generators

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4
Q

What are some symptoms associated with Oculomotor apraxia?

*forebrain disorder

A

Oculomotor apraxia is a frontal eye field problem.

  • will present with trouble making saccatic movements, but can move head or blink to move eyes
  • turn head to see but will overshoot
  • preserved vestibuloocular reflex
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5
Q

What are some symptoms associated with Left CN VI Palsy?

*problem with plant

A

no matter what, pt won’t be able to laterally move left eye b/c problem is with “plant” regardless of if saccade is working, and the pursuit is fine, and the vestibuloocular reflex is intact too.

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6
Q

What are some symptoms associated with Internuclear opthalmoplegia?

*problem with plant

A

problem is due to medial longitudinal fasiculus and with one eye that can’t or at least adducts (moves medially) really slowly.

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7
Q

What are some symptoms associated with bilateral medial longitudinal fasiculus lesion?

*problem with plant

A

aka bilateral internuclear fasiculus lesion

  • normal convergence –> indicates that something else is driving CN III nuclei just fine
  • nystagmus
  • when pt looks right, L eye slowly adducts
  • when pt looks left, R eye slowly adducts
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8
Q

Where do saccadic commands come from?

A

saccadic commands come from frontal eye fields anterior to pre-central gyrus; fibers will synapse at PPRF in pons.

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9
Q
PPRF, the site of synapse of fibers that command saccades has 3 cells:
burst cells
pause cells
tonic cells
describe them
A

1) burst cells –> sends “pulse-step” signal to move eyes
2) pause cells –> inhibits firing of burst cells (if no pause cells = opsoclonus -uncontrollable eye movements
3) tonic cells –> maintain eye positions

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10
Q

Which cells are at fault when there are slowed saccades?

A

Slow saccades are due to problem with burst cells in PPRF aka partial burster loss. In this case, person cannot look up or down, problem w/ convergence, and SLOW HORIZONTAL SACCADES to right or left.

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11
Q

So burst cells –>+ integrator –>+ tonic –> motoneurons: what happens when there’s integrator loss?

A

Burst is there, but there’s no integrator so no new tonic firing rate.

  • will have nystagmus
  • turn eyes to right, he can but eyes slide off & drift back
  • even at rest, there’s jerking
  • slow, drifting off from fixation

*cerebellum plays role in integrator

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12
Q

so pause cells –> - burst cells –>+ integrator –>+ tonic –> motoneurons: what happens when pause cells are lost?

A

No one is inhibiting the burst cells, so will get uninhibited tonic firing, causing involuntary, random chaotic saccades, a condition known as opsoclonus.

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13
Q

Briefly describe the “scene” and the “move” in terms of visual signals being sent and saccade being generated.

A

(The scene) -visual signals –> eye position signals will dictate the size of needed saccade –> (the move) –> saccade generator –> Left and Right plants.

Plants: CN nuclei, burstors, MLF

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14
Q

The type of eye movement that is used to focus vision at different distances is called

A

vergence

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15
Q

In regulating lateral rectus muscle activity, abducens motoneurons fire

A

in bursts during lateral eye movements and at somewhat lower firing rates during lateral displacements.

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16
Q

Lesions of the left frontal eye field results in

A

transient deviation of the eye to the left b/c can’t make saccade movements to right plus a transient contralateral saccade deficit.