DrVirgo
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When you ask the patient to look to the right:
In lesion of Left MLF:
1. Left eye cannot look Right.
2. Right eye exhibits nystagmus
3. CONVERGENCE INTACT (How can this be possible?)
If eyes cant move together how is convergence intact? (Kaplan anat.)
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| infliximab
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THE ACTION-CONVERGENCE IS BY FIBRES OF THE OCULOMOTOR NUCLEUS,WHICH IS DIFFERENT FROM MLF
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| DrVirgo
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Agree.
But if there is a lesion of the MLF, and MLF is higher than the Occulomotor Nucleus, then the MLF can't send fibers down to the Occulomotor Nucleus!
So how is convergence able to be intact in MLF lesion?
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| DrVirgo
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Anyone know?
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| msyamp
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boss who said mlf is higher than occulomotor nucleus?
it is a fasciculus that rums all over the brainstem that connects all the eye muscle nuclii and cerebellum and VIII nerve nucleaus etc. it is rsponsble for the fanous oculocephalic reflex too. now coming to your point the above sgns are due to internuclear opthalmoplegia which is a defect in MLF betweeen abducens nucleaus which is down in pons and oculomotor which is mid bran. the fibreas till midbrain are not affected
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| msyamp
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hey i think you described one and a half syndrome. even then the leison is below occulomotor
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| DrVirgo
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I didn't mean that the MLF is higher physically.
I meant that the MLF (which recieves input from the contralateral abducens nucleus), sends fibers to the ipsilateral Occulomotor Nucleus which then reaches the Ipsi. Medial Rectus. So if there is a problem with the MLF, won't there be a problem with the Occulomotor Nucleus as well?
-The Original post that i described is not 1 1/2 syndrome. Its what happnes when there is a problem with the MLF.
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| Geroo
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well I'm not sure about the convergence pathway but it doesn't go through the MLF inputs go directly to occulomotor nucleus
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| DrVirgo
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OK geroo. I didn't know there was a separate pathway for convergence itself.
That makes sense now. Thanks.
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| msyamp
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HEY 1 AND HAF SYNDROME IS A PROBLEM WITH MLF.
OK LEAVETHAT MLF LEISON DOES NOT NECESSARYILY INJURE OCCULOMOTOR AND ITS CONNECTION TO HIGHER LEVELS.
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| zaidsuror
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Regarding the convergence pathway,it is different as geero mentioned.It comes from the superior colliculus and pretectum and has nothing to do with mlf.
as for one a and a half syndrom its a bilateral mlf lesion + lesion of the abducens nucleas or (PARAMEDIAN PONTINE RETICULAR FORMATION) (ALSO CALLED THE ISPSILATERAL HORIZONTAL GAZE CENTER). so on lateral gaze the only movement is that carried out be intact lateral rectus.
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| Harry Potter
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few points to make things clear- need to know horizontal gaze center, 6th nucleus, MLF, 3rd nucleus and converegence pathway.
To move the eyeball conjugately to one side-LR on one side and MR on other side has to co-operate. The MLF is involed in this. The gaze center for horizontal gaze lies in PPRF which sends signals to 6th nucleus. this nucleus interestingly has 2 sets of neurons- one for the lateral rectus and the other for the contralteral medial rectus nuclei in oculomotor nucleus complex. This group of neurons in the 6th nucleus is a type of interneuron. This sends sgnals via the MLF to opposite MR neurons and thus hels conjugate gaze. The convergence reflex where there is no conjugate gaze, rather dysconjugate gaze ( MR on either side contract together) and hence do not involve this pathway. I am not sure about the precise pathway for the converegence.
Hope this helps.
HP
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