L26: Oculomotor & Motor learning Flashcards
Is frontal eye field tonically active?
Yes
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?
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
What are some symptoms associated with Abnormal Frontal Eye Fields?
*forebrain disorder
-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
What are some symptoms associated with Oculomotor apraxia?
*forebrain disorder
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
What are some symptoms associated with Left CN VI Palsy?
*problem with plant
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.
What are some symptoms associated with Internuclear opthalmoplegia?
*problem with plant
problem is due to medial longitudinal fasiculus and with one eye that can’t or at least adducts (moves medially) really slowly.
What are some symptoms associated with bilateral medial longitudinal fasiculus lesion?
*problem with plant
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
Where do saccadic commands come from?
saccadic commands come from frontal eye fields anterior to pre-central gyrus; fibers will synapse at PPRF in pons.
PPRF, the site of synapse of fibers that command saccades has 3 cells: burst cells pause cells tonic cells describe them
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
Which cells are at fault when there are slowed saccades?
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.
So burst cells –>+ integrator –>+ tonic –> motoneurons: what happens when there’s integrator loss?
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
so pause cells –> - burst cells –>+ integrator –>+ tonic –> motoneurons: what happens when pause cells are lost?
No one is inhibiting the burst cells, so will get uninhibited tonic firing, causing involuntary, random chaotic saccades, a condition known as opsoclonus.
Briefly describe the “scene” and the “move” in terms of visual signals being sent and saccade being generated.
(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
The type of eye movement that is used to focus vision at different distances is called
vergence
In regulating lateral rectus muscle activity, abducens motoneurons fire
in bursts during lateral eye movements and at somewhat lower firing rates during lateral displacements.
