Final answer:
The corticospinal tract splits at the pyramidal decussation. Most fibers cross over to the opposite side and divide into the lateral and anterior tracts, responsible for voluntary movements.
Step-by-step explanation:
The corticospinal tract (CST) is a major descending tract from the brain to the spinal cord, integral for the control of voluntary movements. The fibers of this tract originate from the primary motor cortex, course through the internal capsule, cerebral peduncles, and pons before reaching the medulla, where they comprise part of a white matter tract called the pyramids. The split in this tract occurs at the pyramidal decussation at the junction between the medulla and the spinal cord. Here, most fibers cross over (decussate) to the opposite side before the tract separates, with the majority becoming the lateral corticospinal tract and the rest forming the anterior corticospinal tract.
The anterior corticospinal tract goes on to control the muscles of the trunk, and its axons decussate at the spinal level they exit to go to their respective muscles. The lateral corticospinal tract, which decussates in the medulla, primarily controls the distal musculature. These tracts represent the pathway for upper motor neurons to connect with lower motor neurons, which ultimately mediate skeletal muscle movements.