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Arthritis is a disease that causes joints to swell, stiffen, and become painful. It may also cause the joint to become misshapen. It can be very difficult to move an arthritis-infected joint.

• Pumps blood through your body
• Enables you to breath
• Holds you upright
• Allows you to move

• The muscular system is made mostly of the muscles that allow your body to move and be flexible
• Muscles not part of the muscular system move materials inside your body
• Muscle tissue is made up of muscle cells.
• Muscle cells contain special proteins that allow them to shorten and lengthen

Muscle is the tissue that contracts and relaxes, making movement possible.

Skeletal, smooth, and cardiac. Each are muscle tissues.

• Skeletal muscle is voluntary muscle.
• Smooth and cardiac muscle is involuntary muscle.

Smooth muscle is found in internal organs and blood vessels. It helps move materials through the body. Smooth muscle movement in your digestive system helps move food through your intestines.

• Cardiac muscle is the tissue that makes up the heart.
• Your heart never gets tired like your skeletal muscle.
• Cardiac muscle cells are able to contract and relax tirelessly. They never stop moving your whole life.
• In order to supply lots of energy to the cells, cardiac muscle cells contain many mitochondria.
• The contractions of cardiac muscle push blood out of the heart and pump it around the body.

Skeletal muscle is attached to your bones and allows you to move. Most skeletal muscles work in pairs around joints. One muscle, the flexor, bends a joint. The other, the extensor, straightens the joint. When one muscle contracts, the other relaxes to allow movement of the body part.

A strain is a muscle injury in which a muscle is overstretched or torn. This can happen when muscles have not been stretched properly or when they are overworked. Strains cause the muscle to swell and can be painful. Strains and tears need rest to heal.