Bones come together to form joints. The configuration of a joint determines the degree and direction of possible motion. Some joints, such as those between the plates of the skull, called sutures, don't move in adults. Others allow a range of motion. Other components of joints provide stability and reduce the risk of damage from constant use.
Muscles are bundles of fibers that can contract.
Skeletal muscles, which are responsible for posture and movement, are attached to bones and arranged in opposing groups around joints. Tendons, tough bands of connective tissue, attach each end of a muscle to a bone. Ligaments, which are similar tissues, surround joints and connect one bone to another. They help strengthen and stabilize joints, permitting movement only in certain directions. The components of a joint work together to facilitate movement that is balanced and causes no damage.