RELATIONS BETWEEN STRUCTURE AND FUNCTION IN THE DESIGN OF SKELETAL MUSCLES

Abstract

A histochemical study of the soleus and m. gastro-cnemius (M.G.) muscles of the cat was made, using recently developed methods of staining muscle fibers for ATPase. Three types of fibers differing in size and mitochondrial ATPase content were identified in M. G. Only one of these, type B, intermediate in size and reactivity, was found in soleus. The numbers, diameters and total cross-sectional areas of each type of fiber were determined and observations were made on the intrafusal fibers in their spindles. The histochemical findings provide a background for a detailed functional anaylsis of prior data on motor units in these same muscles. Hypotheses concerning the size, threshold and "usage" of motor neurons and motor units, which emerge from this analysis, offer a rationale for the histological findings. The conjunction of these different observations, all concerned with the same muscles, permits the authors to point out some previously unrecognized principles which govern the design of skeletal muscle.