Point 4











Full Pathway Diagram of LCSTInterruption 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.

Practice DiagramWhat 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!!!!