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ok i posted in another thread a question and got a couple replies but if ANYONE could help me id really appreciate it. Now forgot my other question or if you know please do tell but i have searched far and wide , virtually every neuro book i can find, internet, medline everything and i cannot find an explanation on how VOR and nystagumus work. I konw there are other types but ill use that specific one. Now this is what i do know or i understand. Now VOR reflex is triggered by opposite side so- left canal is stimulated and that sends signals via left vestib nucleus to contralateral abducens nuclues, which connects via mlf to the left CNIII to cause right horizontal gaze upon head turn to left.
Now i also know that for voluntary horizontal gazes-fast saccades of the eye you iniate a signal from the frontal cortext vision center, which sends a message to contralateral PPRF- which then links to the abducens nuclues right next to it on same side(the abducens ipsi to the pprf, which means both pprf and abducens are contralateral to the inital cortex signal. now that triggers the abducens nerve and via mlf the cnIII medial nerve of the other side to have horizontal gaze.
Now back to VOR, so say after, like above a head turn to left, the eyes go right in horizontal gaze and then a nystagmus move back to left as a fast saccadic move to recenter the eyes
NOW here is the QUESTION, this is the part i dont get- i know the nystagmus is signaled by the cortex frontal eye center, just like the voluntary horizontal gaze but I do not understand the connections. My hypothesis was this:
So back to a left heard turn--> causes a VOR to the right from firing right abducens and left cnIII. Now time for nystagmus, now does the Left frontal cortex send a signal to the RIGHT pprf to inhibit the abudens/mlf/cnIII right horizontal gaze produced by the VOR, which would stop the contraction of those muscles and produce a fast "rebound" of the muscles back to the center( to the left in this case).
Now why i believe this is because according to BRS neuro, in bilateral mlf damage causes a monoocular nystagmus- So again say in bilateral mlf damage you turn head to left and trigger a VOR signal of eyes to right-only the abudecs will fire and cause right eye to look right as usual but due to no mlf the CNIII of left side will not be triggered therefore all youll get with a right horizontal gaze from vor( or any horizontal gaze but in this case is VOR) is your right eye looking laterally. Now brus says that right eye will have a nystagmus action back to the left( just like normally occurs in a vor) but the thing is it is monoocular and the left eye neither moves initially due to mlf damage nor does it have a nystagmus reaction.
Now that tells me that there are 2 possibilities for nystagmus path.
1. continuing with this example, the right eye look right after head turns left followed by left beating fast nystagmus is caused by what i said above- LEFT cortext signal to RIGHT pprf INHIBITING the right abducens which stops the abducens lateral rectus from contracting thus " due to decrease lat. rectus contraction- the right eye moves left back to center.
OR
2. the nystagmus is caused by a signal from teh RIGHT frontal cortext to the LEFT pprf which excites the left abducens and via mlf the right cnII medial rectus (assuming no damage) to move the eyes to the left for the fast nystagmus.. BUT NOW THE PROBLEM- is why thsi path doesnt make sense is back to the bilateral mlf damage- if this were the path that causes nystagmus then with bilateral mlf damage you would indeed have only a right eye move right on left head turn with no movement in left medial rectus BUT you would also have a monoocular nystagmus in the LEFT eye that didnt move at all in teh first place and no nystagmus in the right eye that initally moved since the movement to the left would require excitment of the left abducens triggering left lat rectus and via mlf to the cnIII medial rec. to adduct the right eye back to center causing nystagmus but the mlf is GONE therefore this would be impossible, BUT brs says tha monoocular nystagmus IS in the right eye that moved initally in the VOR and the left eye that never moved, never had a nystagmus.. THEREFORE i can only deduce that my first path is feasible.
Now i am sorry i hope someone was kind enough to follow this nonsense and i know this was long but this is really driving me mad and id relaly appreciate some feedback of the nystagmus path with an example.. Thanks so much
Now i also know that for voluntary horizontal gazes-fast saccades of the eye you iniate a signal from the frontal cortext vision center, which sends a message to contralateral PPRF- which then links to the abducens nuclues right next to it on same side(the abducens ipsi to the pprf, which means both pprf and abducens are contralateral to the inital cortex signal. now that triggers the abducens nerve and via mlf the cnIII medial nerve of the other side to have horizontal gaze.
Now back to VOR, so say after, like above a head turn to left, the eyes go right in horizontal gaze and then a nystagmus move back to left as a fast saccadic move to recenter the eyes
NOW here is the QUESTION, this is the part i dont get- i know the nystagmus is signaled by the cortex frontal eye center, just like the voluntary horizontal gaze but I do not understand the connections. My hypothesis was this:
So back to a left heard turn--> causes a VOR to the right from firing right abducens and left cnIII. Now time for nystagmus, now does the Left frontal cortex send a signal to the RIGHT pprf to inhibit the abudens/mlf/cnIII right horizontal gaze produced by the VOR, which would stop the contraction of those muscles and produce a fast "rebound" of the muscles back to the center( to the left in this case).
Now why i believe this is because according to BRS neuro, in bilateral mlf damage causes a monoocular nystagmus- So again say in bilateral mlf damage you turn head to left and trigger a VOR signal of eyes to right-only the abudecs will fire and cause right eye to look right as usual but due to no mlf the CNIII of left side will not be triggered therefore all youll get with a right horizontal gaze from vor( or any horizontal gaze but in this case is VOR) is your right eye looking laterally. Now brus says that right eye will have a nystagmus action back to the left( just like normally occurs in a vor) but the thing is it is monoocular and the left eye neither moves initially due to mlf damage nor does it have a nystagmus reaction.
Now that tells me that there are 2 possibilities for nystagmus path.
1. continuing with this example, the right eye look right after head turns left followed by left beating fast nystagmus is caused by what i said above- LEFT cortext signal to RIGHT pprf INHIBITING the right abducens which stops the abducens lateral rectus from contracting thus " due to decrease lat. rectus contraction- the right eye moves left back to center.
OR
2. the nystagmus is caused by a signal from teh RIGHT frontal cortext to the LEFT pprf which excites the left abducens and via mlf the right cnII medial rectus (assuming no damage) to move the eyes to the left for the fast nystagmus.. BUT NOW THE PROBLEM- is why thsi path doesnt make sense is back to the bilateral mlf damage- if this were the path that causes nystagmus then with bilateral mlf damage you would indeed have only a right eye move right on left head turn with no movement in left medial rectus BUT you would also have a monoocular nystagmus in the LEFT eye that didnt move at all in teh first place and no nystagmus in the right eye that initally moved since the movement to the left would require excitment of the left abducens triggering left lat rectus and via mlf to the cnIII medial rec. to adduct the right eye back to center causing nystagmus but the mlf is GONE therefore this would be impossible, BUT brs says tha monoocular nystagmus IS in the right eye that moved initally in the VOR and the left eye that never moved, never had a nystagmus.. THEREFORE i can only deduce that my first path is feasible.
Now i am sorry i hope someone was kind enough to follow this nonsense and i know this was long but this is really driving me mad and id relaly appreciate some feedback of the nystagmus path with an example.. Thanks so much