The skeletal system provides support to your body, protects your internal organs and works with your muscles to allow you to move. It is made up of bones, joints and cartilage. The full assembly of 206 bones is known as the skeleton.
The skeleton is divided into two major parts: the axial skeleton and the appendicular skeleton. Your spine, or vertebral column, is built of a series of small rounded bones called vertebrae. The axial skeleton includes these vertebrae, along with your skull, ribs and sternum or breastbone. The rest of the bones in your body, including your arm bones, leg bones, hips, shoulders and fingers and toes, make up the appendicular skeleton.
The point where one bone connects to another is known as a joint. Nonsynovial joints are solid joints with little or no room for movement. These joints are usually held together either by ligaments - strong, fibrous tissue - or by cartilage. Cartilage is the flexible tissue that gives structure to your nose and ears. The joints between plates of your skull are nonsynovial joints.
Your ability to move comes from synovial joints. The bones of a synovial joint are separated by a small space filled with fluid that lubricates movement. A thick layer of cartilage prevents the bones from wearing down against each other and helps the joints to bear weight.
Different types of joints allow for different ranges of motion. Your shoulder is a ball-and-socket joint. It allows your arm to rotate in almost any direction. Your knees and elbows are hinge joints. These joints allow a motion similar to the joints in a door, they can open and close, but side-to-side motion is limited. Finally, gliding joints are found mostly between vertebrae. Gliding joints allow the bones to slide or glide against each other so your back can twist and flex, but still remain essentially upright.