Structure and function of musculature

Muscle makes up 40-50% of body mass. It is the tissue which allows one to move the limbs, which is utilized in articulating the joints of the skeleton. On closer examination all the muscles in the human body show biochemical specialization allowing them to perform their particular physiological functions the muscles in the back and buttocks evolved for continuous heavy lifting where fuel economy is important. The eyeballs are steered by extraocular muscles when reading they must contract quickly and precisely. The hollow viscera often require a slow steady squeeze to function properly. The heart muscle must provide continuous circulation of blood for transport of oxygen and nutritive substances. The different muscles in the body can be divided in three main types, which are described in the following. 

Skeletal muscle is under conscious control. Each fibre is an enormous, multi-nucleate cell, formed by fusing hundreds of myoblasts end-to-end. They show a striated pattern, reflecting the regular arrangement of sarcomeres within each cell. 

Cardiac muscle is similar to skeletal muscle, but is not under conscious control. These mono-nucleate cells are much smaller, but still show a striated pattern. The cells are in electrical contact through communicating gap junctions. These are important for the orderly spread of excitation through the heart. Spontaneous electrical depolarization of the specialized pacemaker cells together with conducting fibres activate the bulk of the ventricular muscle in the chamber walls, in each case through direct electrical contacts. 

Smooth muscle is closer to non-muscle cells. No regular striations are visible and the contractions are much slower. Smooth muscle is found in the blood vessels, gut, skin, eye pupils, urinary and reproductive tracts. Smooth muscles form a very heterogeneous group of tissues, and the properties of vascular smooth muscles dilfer greatly from those in the airway, gut or reproductive tract. 

The present work focuses on examinations in skeletal muscle, which makes up the bulk of the body s muscle and is the tissue we use for physical activity. For this reason features of this muscle type are reported in more detail in the following. 

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