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Paul Kim

Corticospinal tract (English)

Corticospinal tract (English)

The corticospinal tract originates from upper motor neurons (UMN) located in the primary motor cortex. The arising fibers form the corona radiata and converge to pass through the posterior limb of the internal capsule into the brainstem. The fibers here pass through the cerebral peduncle, the pons, and the pyramids of the medulla, from which the pyramidal tracts got their name. At the level of the inferior medulla oblongata, the majority (90%) of the corticospinal fibers cross over to the opposite side, an action deemed as the decussation of pyramids. The fibers that cross over continue as the lateral corticospinal tract. About 10% of the fibers that remained on the same side continue as the anterior corticospinal tract. However, these fibers ultimately do decussate at the lower spinal cord levels, close to their destination. At this point, the upper motor neurons (UMN) of both the anterior and lateral corticospinal tracts synapse with the lower motor neurons (LMN) in the anterior gray horn of each level of the spinal cord. The lower motor neurons then leave the spinal cord through the anterior root to form peripheral nerves, which innervate the muscles of the trunk and limbs.
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