The
pyramidal motor system, also called the pyramidal tract or the corticospinal tract, start in the motor center of the
cerebral cortex. There are upper and lower motor
neurons in the corticospinal tract. The motor impulses originate in the giant pyramidal cells or
Betz cells of the motor area; i.e., precentral gyrus of cerebral cortex. These are the upper motor neurons (UMN) of the corticospinal tract. The
axons of these cells pass in the depth of the cerebral cortex to the
corona radiata and then to the
internal capsule, passing through the posterior branch of internal capsule and continuing to descend in the midbrain and the
medulla oblongata. In the lower part of the medulla oblongata, 90–95% of these fibers
decussate (pass to the opposite side) and descend in the
white matter of the
lateral funiculus of the
spinal cord on the opposite side. The remaining 5–10% pass to the same side. Fibers for the extremities (
limbs) pass 100% to the opposite side. The fibers of the corticospinal tract terminate at different levels in the
anterior horn of the
grey matter of the spinal cord. Here, the lower motor neurons (LMN) of the corticospinal cord are located. Peripheral motor
nerves carry the motor impulses from the anterior horn to the voluntary
muscles. ==Extrapyramidal motor system==