Eye Movements - Shorer

Question 1

What are the divisions of the abduscent nerve?

Answer 1

1. Internuclear abduscent nucleus
2. Motor abduscent nucleus

Question 2

What is the medial longitudinal fasciculus (MLF)?

Answer 2

Elongated fibers interconnecting the nuclear areas around CN III and IV and the PPRF

Question 3

What is the connection and decussation of the oculomotor and abduscent nerves?

Answer 3

Oculomotor nerves begin at the cortex and decussate to the contralateral PPRF where they synapse at two abduscent nuclei:

1. Contralateral motor nucleus to contralateral lateral rectus muscle.
2. Ipsilateral internuclear abduscent nucleus to contralateral internuclear abduscent nucleus, through MLF to contralateral oculomotor nucleus to contralateral medial rectus muscle.

End result: left cortex makes eye look right with left medial rectus and right lateral rectus. Right cortex makes the eye look left with the right medial rectus and the left lateral rectus.

Question 4

In which direction does the cortex move the eyes in stimulation and in trauma?

Answer 4

In trauma eyes look towards the injury, in stimulation look away from the stimulated side.

Question 5

What is the effect of demyelination of the medial longitudinal fasciculus (MLF- like for example in MS)?

Gow to examine this injury?

Answer 5

Example injury to left MLF.
Tell patient to look to the left
Activating motor abduscent nucleus and left lateral rectus: OK
Activating contralateral MLF and oculomotor on right side: OK
Tell patient to look right:
Contralateral (right) PPRF, motor nucleus, right oculomotor: OK
Left eye: no stimulation to left oculomotor/medial rectus, CANNOT LOOK RIGHT, stays in midline. Can make jerky eye movements: nystagmus.
Internuclear ophthalmoplegia (between abduscens and oculomotor)
Medial problem of ipsilateral side.
Bilateral MLF
Bilateral problem of medial rectus.
No abduction but adduction is OK.

Question 6

What part of the brain controls saccades?

controls smooth pursuit?

Controls other aspects of sight (color, speed, etc.)?

stores memory?

Answer 6

Saccades: Contralateral frontal eyefield

Smooth pursuit: Contralateral parieto occipital area

Color, speed, etc: Occipital pole (Brodmann 18/19)

Memory: temporal area