oculomotor and motor learning Flashcards
what is convergence?
when eyes come together in the center occurs together ( driven by something above the third nerve ( not the mlf)
what is the only thing preserved in bilateral internuclear opthalmoplegia and why ?
convergence only CN II and III are used not CN VI
what is internuclear opthalmoplegia and give a description of how it works?
disconjugate horizontal gaze due lesion of Medial longitudinal fasciculus (MLF) or Parapontine reticular formation ( PPRF)
ex. R. eye will not adduct when asked to look left voluntarily, but can move when
following a finger (CN VI is preserved)
what is OKN, OptoKinetic Nystagmus?
the eyes can jump focus, ex. switching targets as we walk - also steadies the scene against movement
what are saccades and what determines the rate of them?
Fast eye movements to shift the visual scene onto the fovea
- the forebrain decides where saccades should go ( when and where we look)
Frontal Eye Field controls ?
voluntary eye movements
Superior Parietal Cortex controls?
involuntary pursuit movements
where is the vertical gaze center?
Vertical gaze center/saccade generator is in the midbrain ( nucleus of cajal)
where is the horizontal gaze center?
Horizontal gaze center is in the PPRF
what do vergence and Accomodation do?
adjust the plane of focus
what is Oculomotor Apraxia?
lesion to frontal eye fields & loss of voluntary eye movements
can’t voluntarily move eyes e.g. can’t “look right” on command but can still follow a finger to the right
what happens to the visual ocular reflex in oculomotor apraxia?
- Visual ocular reflex preserved. Patient often “exceeds target” as they turn their head to try and
see an object in their periphery. Also will see them blinking to break the VOR
and shift their gaze.
what occurs in Left CN VI Palsy?
N VI damage
- the eye can’t move laterally, either voluntarily or involuntarily
what is characteristic of Forebrain problems ?
symmetrical, conjugate problems.
what is characteristic of nerve or nuclei problems?
disconjugate movements, diplopia
how does the saccade generator work?
A saccade requires both a “burst” of firing to overcome inertia and initiate eye movement + a new “tonic” firing rate to maintain the new position ( see image on page 988)
there is a burst of activity and a new firing rate which is the integral of the speed of the burst activity
what happens if the pause cells aren’t working?
opsoclonus: make random saccades , could be congenital and get better or could not be congenital
what type of problems do you get when saccade generator isn’t working?
brainstem problems
what hppens when there is a problem with burst cells?
slow saccades
what happens when there is a problem with the integrator?
eye moves but can’t keep it there so it drifts back
What types of info/ control does the cortex give/have to/on the saccade generator?
Motor Error: difference between current visual
field and where you want to look
Trigger: tells the eyes when to move (ex. pretty woman at the mall…)
problems with what four things can cause diplopia?
mlf, burster cells, cranial nerves, cranial nuclei
