TEMPORAL AND SPATIAL SUMMATION IN AUTONOMIC SYSTEMS

Abstract

Isotonic and isometric contractions of the nictitating membrane, heart-rate inhibition and isometric contractions of skeletal muscle at varying frequencies of maximal stimulation, before and after severance of a fraction of the nerve supply, were recorded from cats. The analysis of the curves thus obtained leads to the following con clusions: Smooth muscle, unlike skeletal muscle, is not organized as motor units. In smooth muscle any nerve fiber of the motor supply can cause contraction of all the cells, within certain limitations. Smooth muscle does not follow the all-or-none principle. The differences between skeletal and smooth muscle are explained by a free diffusion throughout the latter of a chemical mediator liberated by the nerve impulses. This theory adequately covers other autonomic systems (heart-rate inhibition) . The responses of autonomic systems are a function of the number of nerve impulses delivered per unit time, regardless of the number of nerve fibers involved. A given destruction of the nerve supply impairs the responses of smooth muscle less than those of skeletal muscle. Fatigue in smooth muscle probably affects first the contractile system, not the myoneural junction.