The neuromuscular system

This chapter deals with the history of neuromuscular system and its events along with the people involved. The muscle system is held responsible for generating force and moment. Moreover, the chapter emphasizes on the events in the muscles and motoneurons. Herophilus (early third century B.C.) has been the first to recognize the involvement of muscles in producing movements and to distinguish between nerves and tendons, as well as between arteries and veins. It was Galen (129-199 A.D.), however, who took the understanding of muscles and nerves carrying out public dissections of human bodies, he experimented on live animals and African monkeys in particular. Henneman was responsible (with Lome Mendell) for pioneering spike triggered averaging, a technique, which has had many applications, including the demonstration of the size principle in human interosseous muscles by Stein. The smallest motor units were the first to be called upon slowly developing contractions, and in certain reflexes. The histochemical analysis of the hindlimb muscles revealed that a steady exercise of moderate intensity (running) made greatest use of slow twitch-oxidative (type I) fibers and maximal intermittent activity (jumping) depended heavily on fast twitch-glycolytic (type IIB) fibers. In the naturally occurring contraction, there was also a progressive reduction in the rate at which the muscle fibers were excited by the motoneurons and that was optimal for delaying fatigue. In some subjects that either electrical stimulation or a supreme effort added increasing amounts of tension as fatigue, progressed during voluntary contractions of the adductor pollicis and quadriceps muscles. Inactivity causes muscles to atrophy and that an even greater loss of bulk may follow nerve damage or disuse. By combining measurements of muscle enzyme activity with those of messenger RNA, continuous muscle stimulation could elevate enzyme activity so rapidly that an increased translation of messenger RNA is involved, with the effects of altered gene expression appearing later. If the maximal rate of shortening is reduced, as in fatiguing muscle, then power must necessarily decline. Also, at the progressively higher rates of limb movement, the contributions of the fast contracting muscle fibers (type II; FF and FR) to power output become increasingly important. Such studies have shown, that shortening contractions, in which power is developed, are more fatiguable than isometric contractions and that this is reflected in greater biochemical changes in the fibers. © 2003 American Physiological Society Published by Elsevier Ltd All rights reserved.