Which deficits in the primary (corticospinal) efferent system result in movement disorders?

Updated: Aug 20, 2019
  • Author: Morris Steffin, MD; Chief Editor: Jonathan P Miller, MD  more...
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The primary, or direct, system includes predominantly excitatory output from large pyramidal cells projecting directly to the spinal motor neurons. However, corticocortical inhibition plays a significant role in modulating motor behavior at this level, and the projections of excitatory pyramidal cells are plastic and are modulated by function. This is somewhat contrary to what had been suggested by previous conceptions of homuncular anatomy. Plastic effects also, of course, involve connections from supplementary motor and other cortical regions. Impairment in these regions also produces paresis.

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