The largest descending fiber tract {corticospinal motor tract} has one million axons from primary motor, supplementary motor, and premotor cerebral cortex layer-5 pyramidal neurons to spinal cord segment neurons to control precise finger and toe movements. Spinal-cord axons initiate skilled muscle movements at alpha motor neurons. Pre-central gyrus has the most corticospinal motor-tract neurons.
Lateral corticospinal tract, only in mammals, controls voluntary muscles. Anterior corticospinal tract does not cross over and is for posture and trunk position.
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Date Modified: 2022.0224