JOINTS

Joints:
You may sit at a table, pick up a sandwich, bite off a piece of a carrot and chew it, and walk to class. All of these motions are possible because your skeleton has joints.
Anyplace where two or more bones come together is a joint. The bones making up healthy joints are kept far enough apart by a thin layer of cartilage so that they do not rub against each other as they move. The bones are held in place at these joints by a tough band of tissue called a ligament. Many joints, such as your knee, are held together by more than one ligament. Muscles move bones by moving joints.

Immovable Joints:
Refer to Figure as you learn about different types of joints. Joints are broadly classified as immovable or movable. An immovable joint allows little or no movement. The joints of the bones in your skull and pelvis are classified as immovable joints.

Movable Joints:
All movements, including somersaulting and working the controls of a video game, require movable joints. A movable joint allows the body to make a wide range of motions. There are several types of movable joints—pivot, ball and socket, hinge, and gliding. In a pivot joint, one bone rotates in a ring of another bone that does not move. Turning your head is an example of a pivot movement. A ball-and-socket joint consists of a bone with a rounded end that fits into a cuplike cavity on another bone. A ball-andsocket joint provides a wider range of motion than a pivot joint does. That’s why your
legs and arms can swing in almost any direction. A third type of joint is a hinge joint. This joint has a back-and-forth movement like hinges on a door. Elbows, knees, and fingers have hinge joints. Hinge joints have a smaller range of motion than the balland- socket joint. They are not dislocated as easily, or pulled apart, as a ball-andsocket
joint can be. A fourth type of joint is a gliding joint in which one part of a bone slides over another bone. Gliding joints also move in a back-andforth motion and are found in your wrists and ankles and between vertebrae. Gliding joints are used the most in your body. You can’t write a word, use a joystick, or take a step without using a gliding joint.

Common Joint Problems:
Arthritis is the most common joint problem. The term arthritis describes more than 100 different diseases that can damage the joints. About one out of every seven people in the United States suffers from arthritis. All forms of arthritis begin with the same symptoms: pain, stiffness, and swelling of the joints. Two types of arthritis are osteoarthritis and rheumatoid arthritis. Osteoarthritis results when cartilage breaks down because of
years of use. Rheumatoid arthritis is an ongoing condition in which the body’s immune system tries to destroy its own tissues.