Your Joints
The place where two bones meet is called a joint. There are moving joints that move and fixed ones that don't.

Fixed joints are fixed in place and don't move at all. Your skull has some of these joints (called sutures, remember?), which close up the bones of the skull in a young person's head. One of these joints is called the parieto-temporal (say: par-eye-ih-toh tem-puh-rul) joint - it's the large one that runs around the sides and back of the skull.

Moving joints are the ones that let you ride your bike, eat cereal, and play a video game - the ones that allow you to twist, bend, and move different parts of your body. Some moving joints, like the ones in your spine, move only a little. Other joints move a lot. One of the main types of moving joints is called a hinge joint. Your elbows and knees each have hinge joints, which let you bend and then straighten your arms and legs. These joints are like the hinges on a door. Just as most doors can only open one way, you can only bend your arms and legs in one direction. You also have many smaller hinge joints in your fingers and toes.

Another important type of moving joint is the ball and socket joint. You can find these joints at your shoulders and hips. They are made up of the round end of one bone fitting into a small cup-like area of another bone. Ball and socket joints allow for lots of movement in every direction. Make sure you've got lots of room, and try swinging your arms all over the place.

Have you ever seen someone put oil on a hinge to make it work easier or stop squeaking? Well, your joints come with their own special fluid called synovial fluid (say: si-no-vee-ul) that helps them move freely. Bones are held together at the joints by ligaments (say: lih-guh-mints), which are like very strong rubber bands.