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In Brown sequard syndrome, why does ventral horn destruction lead to ipsilateral flaccid paralysis of somatic muscles(LMN) rather than


i'll try first....Brown Sequard is a hemisection of the spinal cord......the damage occurs in the corticospinal tracts (ventral horn) after the fibres hv crossed over in the a lesion anywhere after tht point is gonna gv u an IPSIlateral paralysis.....tht make sense?


yes, but i've another q.

there is also a lateral corticospinal tract transection in BrownSequard which causes ipsilateral spastic paralysis below the UMN lesion with babinski's sign.

so why ipsilateral here?


is ventral horn above the medulla or below?


wel ya kaplan doesny mention that, but u re right drk... that the lesion is below the level of the crossing hence the fibres have already crossed. think of the spinothalmic fibres which cross at the same level and hence we get contralateral pain and temp loss


but the ventral corticospinal tract results in minor contralateral muscle weakness below the lesion.

so the ventral horn is not the same as ventral corticospinal tract?


i'm not sure i hv completely understood ur Q skyhigh. i'll try n tell u my concept anyhow...
for ur 2nd query...i hv already mentioned why its ipsilateral. whether the hemisection is at the level of LMN(ventral horn) or UMN(desc corticospinal tracts in the lateral white matter)the fibres hv already crossed at the medulla-S.Cord junction so the effect will be ipsilateral. Anywhere above the decussation.....the effect will be contralateral(C/L).

for ur 3rd query....ventral horn is in the spinal cord....def below the medulla...wch is the brain stem!

abt ur last post...i'll hv to chk up on how CST can cause C/L muscle weakness....hdnt known this. is teh ventral horn the same as corticospinal tract(CST)? ....the CST tract runs down the S.C in the lateral part of the white matter....the ventral horn is the gray matter wch will receive axons from the CST tht will be exiting to supply muscles at tht the ventral horn they synapse on LMN.....wch contains the alpha and gamma motor neurons sending fibres to the NMJ and forming the muscle reflex arc. also thru the ventral horn the preganglionic autonomic fibres exit teh S.C.

ths is in Kaplan anat. will appreciate corrections if any...


hemisection of the SC, CST- crosses to the contralateral side in the medulla so a lesion in the spinal cord would cause ipsilateral spastic paralysis below the site of the lesion and at the level of the lesion flaccid paralysis.
DML- crosses medulla to the contralateral side, lesion in the spinal cord would cause ipsilateral loss of sensations ( except pain and temp ) at and below the level of the lesion.
ST Tract- each neuron crosses to the contralateral side in the spinal cord at its segment a lesion in the spinal cord would result in ipsilateral loss of pain and temp at the level of the lesion and loss of pain and temp 2 segments below the level of the lesion on the contralateral side.
I do not know whether I have answered the question as I did not understand what is being asked ...just said what I know abt brown sequard.


Skyhigh is confused between ventral horn and ventral CS tract- for practical purposes, ventral CS tract does not exist as it has no clinical effect whatsoever is the damage.

Ventral horn as drk said, is a collection of grey matter destined to supply the muscles in a particular segment-this ventral horn has the anterior horn cells and are present throuhgout the spinal cord. Its involevement will produce ipsilateral LMN weakness at the level of lesion of the BS syndrome. for e.g if the cord is hemotransected at C% levels, one will get a LMN weakness of msucles supplied by C5 myotome and UMN weakness below that level ipsilaterally (as the CS tract has already crossed). CS tract sends signals to the anterior horn cells in the ventral horn and compelte the motor circuit.


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