Muscle Physiology

In order to understand how skeletal muscles work to produce to movement in the body – so called macro-properties – it is necessary to understand what happens at a microscopic level. In this lecture I will describe the microscopic anatomy of muscle and start to explain what we think is going on at a cellular level to bring about muscle contraction. The basic structure of muscle is shown in figure 1. The muscle belly is a bundle of bundles: the bigger bundles are called fascicles and each fascicle is a bundle of muscle fibres. The coverings of each bundle also have names with the epimysium covering the muscle itself, the perimysium covering the fascicle and the endomysium covering the fibres. Unlike most tissues in the human body the muscle fibre does not consist of a large number of cells. Instead the cell membranes have fused together to produce one large 'supercell' or syncytium containing multiple nuclei. The remaining outer cell membrane is called the sarcolemma and the contents are called sarcoplasm. Within the fibre individual contractile units are called myofibrils.