Corticospinal fibers-a medullary lesion that results in weakness of the extremities on one side indicates involvement of the corti-cospinal fibers located in the pyramid on the contralateral side; these fibers largely cross in the pyramidal (motor) decussation. rubrospinal and vestibulospinal fibers influence the activity of spinal motor neurons, but isolated lesions of these fibers would not result in a unilateral weakness of upper and lower extremities. the anterolateral system and the medial lemniscus are sensory tracts.(p.103109,112)
