Interruption of the LCST means that neurons
in the spinal cord that innervate or drive muscles have lost
a tremendously important input. These muscles are still
innervated by the spinal cord neurons in the ventral horn,
but these cells have lost a large part of their drive This
results in weakness in those muscles that are innervated
by spinal neurons that have lost their LCST excitatory
drive. Such a lesion does NOT result in paralysis because
the muscles are still ALIVE. The problem is that the neurons
that innervate the muscles have lost a large part of their
drive. (There are still some other inputs to these
cells).
It is important to understand that lesions of the LCST at
different levels of the spinal cord result in different
muscles being affected. Let's start with a lesion at C1.
Such a lesion will interrupt ALL of the LCST
fibers to the spinal cord on the SAME side as the
lesion. The result is a loss of voluntary control of all of
the muscles on the IPSILATERAL (to the lesion) side
of the body. This is called HEMIPLEGIA (plegia =
stroke). Notice that the muscles are not paralyzed, only
weak.
What about a lesion of
the LCST at T3. Such a lesion spares the voluntary control
to the upper extremity since the LCST fibers to the spinal
neurons innervating the cervical enlargement have "already
gotten off" and are doing their job. Only the
IPSILATERAL lower extremity is affected. Play
around and sketch some lesions at different rostrocaudal
locations in the LCST. This is a good way to learn!!!!
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