The corticospinal tract is a white matter motor pathway starting at the cerebral cortex that terminates on lower motor neurons and interneurons in the spinal cord, controlling movements of the limbs and trunk. There are more than one million neurons in the corticospinal tract, and they become myelinated usually in the first two years of life.
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The primary purpose of the corticospinal tract is for voluntary motor control of the body and limbs.
However, connections to the somatosensory cortex suggest that the pyramidal tracts are also responsible for modulating sensory information from the body.
Because most (75-80%) of the connections cross the midline at the level of the medulla and others at the level of the spinal cord, each side of the brain is responsible for controlling muscles on the opposite side of the body.
After patients are lesioned in some part of the pyramidal tracts, they are paralyzed on the corresponding side of the body. However, they can re-learn some crude, basic motions, just no fine movements.
This implies that the connections to these tracts are crucial for fine movement, and only partial recovery is possible if they are damaged.