Tissue that contracts is called muscle. Muscles make movement of the body and its parts possible. There are three kinds of muscles. They are skeletal, smooth, and cardiac. These kinds of muscles differ by where they are located, how they work, and what they look like. Skeletal muscles work as opposing pairs of muscles - as one contracts, the other will relax. This allows movement in two directions, in-out, back-forth, up-down.

Cardiac muscle is found only in the heart. Smooth muscle is found in many of our internal organs. Notice that it does not have striations.

Muscle is often described by how it works. Muscle that can be controlled is called voluntary and that which is not consciously controlled is called involuntary. Which type(s) of muscle are voluntary? Which type(s) are involuntary?

Notice the cross wise markings on the muscle fibers in the microscopic views. These markings are called striations. Skeletal and cardiac muscle have these markings.