Friday, October 30, 2009

Decussation of the Pyramids

The decussation of the pyramids, or motor decussation, is the crossing over of cortical motor nerve fibers of the pyramidal tracts at the lower end of the medulla oblongata. About three-fifths of these pyramidal fibers leave the pyramids in successive bundles, and cross over to the opposite side in the anterior median fissure of the medulla oblongata, forming what is known as the pyramidal decussation. As a result, each of the anterior funiculus in the spinal cord is composed of motor fibers that originally come from the opposite side. The two pyramids consist of motor fibers which goes from the cerebral cortex to the medulla oblongata (via cerebral peduncles and pons) and to medulla spinalis, corticobulbar and corticospinal fibers. The word "decussation" means crossing, an X-shape crossing.

Decussation of the pyramids

Cross Section of Decussation of the Pyramids