Muscular System

The Muscular System
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The muscular system allows us to move. Adults have a certain fixed number of muscle cells, approximately 602. . Through exercise, such as weight lifting, the cells enlarge but the number of cells does not increase.

Structure and Function
There are three types of muscle tissue—smooth, skeletal, and cardiac.   Each has its own distinctive function, and therefore, its own distinctive structure, but all muscles allow movement of some kind.

    Skeletal Muscle
Skeletal muscle is called voluntary because you can control this type of muscle. You can voluntarily choose to move them.   These muscles attach to bones, move the skeleton, and are found in the arms, legs, neck, or anywhere you can voluntarily move a body part. These muscles produce strong contractions.

Structurally, these muscle fibers appear striated (striped) when magnified, have more than one nucleus, and may be up to 30 cm long in humans.   Look at the table in this lesson that compares the features of the three types of muscle
tissues.

    Smooth Muscle
Smooth muscle is called involuntary muscle because you can not control this type of muscle movement.   These muscles line internal organs, blood vessels, and organs such found in the digestive and reproductive systems.

Structurally, these muscle fibers appear non-striated (not striped) when magnified, have one nucleus per cell, and are usually short. They produce weaker contractions.

          Cardiac Muscle
Cardiac muscle tissue is involuntary muscle and found, as its name would suggest, only in the heart.   You can not control your heart muscle; it works automatically for you.

Structurally, these muscle fibers appear striated when magnified, have more than one nuclei per cell, and are also branched in appearance.
Muscle contraction mechanisms

How do muscles of any kind contract?   What makes the muscle cells work together to move?

Muscle fibers are made up of alternating patterns of thick... [continues]

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