The neuromuscular basis of lobster swimmeret beating

The anatomy and innervation of the swimmeret muscles of the lobster Homarus americanus were studied using histological and intracellular recording techniques. Each swimmeret is controlled by 12 muscles, each of which comprises from one to five anatomically‐distinguishable bundles of muscle fibers. The bundles which make up each muscle are usually merged along part of their lengths. Sometimes, however, bundles which share efferent innervation and which are therefore part of a single functional muscle are separate along their entire lengths. Thus, the concept of a muscle as a discrete anatomical unit is of limited use in the swimmeret system. The pattern of neuromuscular activity underlying swimmeret beating was determined by recording the rhythmic movements of a swimmeret simultaneously with the electrical activity of its muscles. Each muscle is active for a fixed fraction of every movement cycle, during which it discharges several muscle potentials. The 12 muscles of each swimmeret are recruited in the same temporal sequence during each cycle of swimmeret beating.