MODULE 5
THE LATERAL PATHWAY
The Lawrence and Kuypers model (Figure 5-1) postulates that there are two descending motor systems and the components of the two systems are summarized very clearly in Blumenfeld's Table 6.3. The main component of the lateral system is the lateral corticospinal tract and this is primarily involved in initiating movement of the extremities. But since section of the pyramidal tract at the level of the cerebral peduncle in man leads to only minor loss of motor function Lawrence and Kuypers concluded that there must be a second motor pathway "in parallel with" it and their lesion studies seemed to identify this as cortico-rubro-spinal pathway. This Module was written to be consistent with the Lawrence and Kuypers story, but it is now less certain that the cortico-rubro-spinal pathway is, in fact, the one that "takes over" motor function when the lateral corticospinal tract is damaged. The whole question of the recovery of motor function following "strokes" is of enormous interest these days, and we are leaving this section in the module to give you something of the background. If the cortico-rubro-spinal pathway doesn't account for the rather good motor function that remains following section of the cerebral peduncle, what does explain it?
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