Muscular System

In the muscular system, there are voluntary and involuntary muscles. We can control movements of the skeleton using voluntary muscles, as in bending an arm. We have much less control over our involuntary muscles, including movements within internal organs of the body such as the heart.

Muscles of the human body help to create movement and fall into three different categories. Skeletal muscle moves the body skeleton in the external environment. Smooth muscle controls movement within the body such as moving nutrients and waste through the intestines. Cardiac muscle is the muscle of the heart.

Muscles are made of fibers that are actually long cells in varying shapes that can stretch the length of the muscle. When a nerve impulse reaches a muscle fiber, the fiber shortens, creating a muscle contraction, which then causes movement in the body.

Muscle cells within a given muscle (such as the biceps muscle) work together to provide different degrees of contraction strength. There is almost always an antagonist (in this case, the triceps muscle): a muscle that works to oppose the other to make for a more smooth action or to return the bone to the original position.

Cardiac muscle cells are highly specialized in their function and their makeup. They contract over and over without fatigue in a systematic way so that blood will move through the heart chambers in a regulated manner.