A sarcomere is the basic functional within muscle cells. This unit is distinctive in some types of muscle tissue. It can be observed on microscope slides due to the striated nature of both skeletal muscle and cardiac muscle. (Although smooth muscle has a similar contractile mechanism, is not as highly organized and does not show striations).

The striations are caused by alignment of bands. The most prominent striations are due to the A bands, the I bands, and the lines of Z discs. The unit between two Z lines is called a sarcomere.

In the A band the proteins actin and myosin are both present whereas the I band contains only actin.

Above: Diagram of the unit within a muscle cell that is known as a sarcomere.

Above: Diagram of the unit within a muscle cell that is known as a sarcomere.

When muscle contracts the sarcomere shortens and the lines of the Z discs move closer together.

For further information: features an interesting article about measuring the length of a sarcomere using laser diffraction.

This section consists of short summaries about the structures that form the muscles of the body. This list is not exhaustive but is intended to be appropriate for students of A-Level Human Biology, ITEC courses in massage and related subjects, and other courses in health sciences. For more general information about muscles see the pages about:

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