Spontaneous electrical activity: an overview.

Spontaneous electrical activity of muscle originates either from one, a few, or a large number of muscle fibers; the responses from the latter are similar to those of motor units. Responses from one or a few fibers are those arising in the end-plate zone of normal muscle and the electrical activity is associated with denervation and myotonia. The motor unit-like activity may either be discharged at randomly varying intervals, as in fasciculations, or at intervals similar to the discharges during voluntary effort, as in hemifacial spasm, Isaacs' syndrome, and in infantile spinal muscular atrophy.