The spinal cord has a characteristic structure and functions that are distinct from those of the brain. Its functions are tremendously important since it modulates the peripheral sensory inputs to the dorsal horn, and it gives rise to the ascending pathways transmitting peripheral afferent inputs to the brain, and conveys the descending pathways from the brain both to the lower motor neurons, the final common pathway, and to dorsal horn sensory neurons. In spite of these vital functions, the spinal cord constitutes only a small percent age of the mass of the human central nervous system and...