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Muscles

Muscles function to produce force and motion. They are primarily responsible for maintaining and changing posture, locomotion, as well as movement of internal organs, such as the contraction of the heart and the movement of food through the digestive system.

PubMed Health Glossary
(Source: Wikipedia)

Sketch of arm muscles and ligaments. Click to enlarge

The muscles and ligaments in the arm National Institutes of Health

Structure of a skeletal muscle Click to enlarge

Structure of a skeletal muscle National Institutes of Health

About Muscles

There are more than 600 muscles in the body, which together account for about 40 percent of a person's weight.

Most skeletal muscles have names that describe some feature of the muscle. Often several criteria are combined into one name.

Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction. The integrated action of joints, bones, and skeletal muscles produces obvious movements such as walking and running. Skeletal muscles also produce more subtle movements that result in various facial expressions, eye movements, and respiration.

In addition to movement, muscle contraction also fulfills some other important functions in the body, such as posture, joint stability, and heat production. Posture, such as sitting and standing, is maintained as a result of muscle contraction. The skeletal muscles are continually making fine adjustments that hold the body in stationary positions.

The tendons of many muscles extend over joints and in this way contribute to joint stability. This is particularly evident in the knee and shoulder joints, where muscle tendons are a major factor in stabilizing the joint. Heat production, to maintain body temperature, is an important by-product of muscle metabolism. Nearly 85 percent of the heat produced in the body is the result of muscle contraction.

In the body, there are three types of muscle: skeletal (striated), smooth, and cardiac.

Skeletal muscle: Skeletal muscle, attached to bones, is responsible for skeletal movements.

Smooth muscle: Found in the walls of the hollow internal organs. Smooth muscle cannot be controlled consciously. Smooth muscle contracts slowly and rhythmically.

Cardiac muscle: Found in the walls of the heart. The contraction of cardiac muscle is involuntary, strong, and rhythmical. NIH - National Cancer Institute

Terms to know

Blood Vessels
Tubes that carry blood to and from all parts of the body. The three main types of blood vessels are arteries, capillaries, and veins.
Bone
A living, growing tissue made mostly of collagen.
Cardiac Muscle (Heart Muscle)
Found in the walls of the heart. The contraction of cardiac muscle is involuntary, strong, and rhythmical.
Endomysium
The endomysium is a wispy layer of connective tissue that ensheaths each individual muscle fiber or muscle cell. It also contains capillaries and nerves. Endomysium is the deepest and smallest component of connective tissue.
Epimysium
Skeletal muscle is surrounded by a connective tissue sheath called the epimysium.
Fiber
Ligaments
Band of fibrous tissue connecting bone to bone or cartilage to bone thereby supporting or strengthening a joint.
Locomotion
Movement or the ability to move from one place or another. It can refer to humans, vertebrate or invertebrate animals, and microorganisms.
Muscle Fascicle
Muscle fascicle is a bundle of muscle fibers.
Perimysium
Perimysium is a sheath of connective tissue that groups muscle fibers into bundles (anywhere between 10 to 100 or more) or fascicles.
Peristalsis
A wavelike movement of muscles in the gastrointestinal (GI) tract. Peristalsis moves food and liquid through the GI tract.
Skeletal Muscle
Skeletal muscle, attached to bones, is responsible for skeletal movements. These muscles are under conscious, or voluntary, control. Each consists of skeletal muscle tissue, connective tissue, nerve tissue, and blood or vascular tissue.
Smooth Muscle
Found in the walls of the hollow internal organs such as blood vessels, the gastrointestinal tract, bladder, and uterus. Smooth muscle cannot be controlled consciously and thus acts involuntarily. Smooth muscle contracts slowly and rhythmically.
Striated Muscle
Muscle tissue that appears striped under the microscope.
Tendons
Tough, fibrous, cord-like tissue that connects muscle to bone or another structure, such as an eyeball. Tendons help the bone or structure to move.

Terms to know

Blood Vessels
Tubes that carry blood to and from all parts of the body. The three main types of blood vessels are arteries...
Bone
A living, growing tissue made mostly of collagen....
Cardiac Muscle (Heart Muscle)
Found in the walls of the heart. The contraction of cardiac muscle is involuntary, strong, and rhythmical....
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