Joy to My Joints
The place where two bones meet is called a joint. There are two types of joints in every person's body: fixed joints and moving joints.

Fixed joints are exactly as they sound - they are fixed in place and don't move at all. Your skull contains some of these joints (called sutures, remember?), which close up (or fuse) the bones of the skull together in a young person's head. One of these joints is called the parieto-temporal (say: par-eye-ih-toe tem-por-ull) joint - it's the large one that runs around the sides and back of the skull.

Moving joints are the ones that allow you to ride your bike, eat cereal, plant a flower, and play a video game - the ones that allow you to twist, bend, and move different parts of your body. One of the main types of moving joints is called a hinge joint. Your elbows and knees each have a hinge joint, 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, to allow them to bend. Another important type of moving joint is the ball and socket joint. These joints are at your shoulders and hips, and they are made up of the round end of one bone fitting into a small cuplike 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 every which way.

Have you ever seen an adult put oil on a hinge to make it work easier or stop squeaking? Well, luckily, your joints come with their own special fluid called synovial fluid (say: si-noh-vee-ell) that helps them move freely. There is also some cartilage between ones that are in contact with one another that helps the bones move smoothly. Bones are held together at the joints by ligaments (say: lig-uh-mints), which are like very strong rubber bands.

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