Main muscle types

Muscle tissue

Muscle is composed of 75% water, 20% protein, and 5% mineral salts, glycogen and fat.

Muscle types and function

There are three types of muscle tissue: skeletal, cardiac and smooth. All muscle cells have an elongated shape and are therefore referred to as muscle fibres.

Smooth/unstriated/involuntary muscle

Smooth muscle cells are usually spindle-shaped, and arranged in sheets or layers. Smooth muscles are found in the viscera, i.e. stomach, small and large intestines, blood vessels and uterus (i.e. the hollow organs).

Smooth muscle in the blood vessels contracts to move the blood in the arteries. Smooth muscle also squeezes substances through the organs and tracts. They are under involuntary control (although some individuals can train their minds to achieve some control over smooth muscle contractions). Contractions are usually gentle and rhythmic, with the obvious exceptions of vomiting and birth contractions.

Cardiac/striated/involuntary muscle

Cardiac muscles are found in the heart only, and exist to pump the heart. They are under involuntary control. Structurally they are made up of branching fibres that are striated in appearance and are separated or interspersed by discs, known as intercalated discs.

Skeletal/striated/voluntary muscle

Skeletal muscles (also called somatic muscles) attach to, and cover over, the bony skeleton. They are under voluntary control. Skeletal muscles fatigue easily, but can be strengthened. They are capable of powerful, rapid contractions, and longer, sustained contractions. Skeletal muscles enable us to perform both feats of strength and controlled, fine movements.

Note: as they contract, all muscles generate heat, and this heat is vitally important in maintaining a normal body temperature. It is estimated that 85% of all body heat is generated by muscle contractions.