When a ventral horn cell of the spinal cord is destroyed by the virus of poliomyelitis, all muscle fibers normally innervated by the affected neuron degenerate and ultimately disappear. It is not widely appreciated that muscles responsible for locomotor movements are made up of clusters of skeletal muscle fibers which receive innervation from single anterior horn cells. The ultimate physiologic unit of the reflex, therefore, is not the single muscle fiber but rather the group of muscle fibers controlled by one ventral horn cell; to designate such groups, Eccles and Sherrington1 have introduced the convenient term "motor unit." They have found, after causing all sensory fibers from a given muscle to degenerate, that the motor nerve fibers to a skeletal muscle can be counted, and it was incidentally disclosed that the nerve supplying such a muscle actually contained more fibers near the muscle than at more proximal points. From
PHYSIOLOGIC ANATOMY OF POLIOMYELITIS. JAMA. 1941;117(23):1980–1981. doi:10.1001/jama.1941.02820490054017
Customize your JAMA Network experience by selecting one or more topics from the list below.
Create a personal account or sign in to: