Muscle Excitation and Contraction

Abstract

In the most primitive muscle cells, the myocytes of sponges, contractile phenomena are entirely regulated at a cellular level. In contrast, in all higher phyla, motility is more or less under the control of the nervous system which communicates with muscle cells at the neuromuscular junction. Think, for example, of a frog jumping into a pond. Nerve impulses reaching the motor end-plates of its leg muscles cause the release of acetylcholine from the nerve endings. The neurotransmitter released by a nerve impulse then elicits a small potential change in the membrane of the muscle fibres, the end-plate potential, which in turn evokes a propagated action potential exciting the muscle fibres. This event is followed by the processes of excitation-contraction coupling (Sect. 1.2) and contraction (Sect. 1.3) in which muscle cell calcium (Fig. 1.1) plays a pivotal role.