Year 1 · Support and movement · Section 4.1

The skeleton

The structure of the skeleton

The human skeleton, or skeletal system, consists of about 200 bones. A typical adult has 206, although the number can vary slightly.

Head, trunk and limbs

The body can be divided into three main regions:

• Head: Contains the skull, including the upper and lower jaws.
• Trunk: Includes the spine, with cervical, thoracic and lumbar vertebrae, followed by the sacrum and coccyx. The thoracic vertebrae, ribs and sternum form the rib cage. The shoulder girdle consists of the collarbones and shoulder blades. The pelvis includes the hip bones, sacrum and coccyx.
• Limbs: Arms and legs have corresponding sets of bones. The arm contains the humerus, radius, ulna and hand bones. The leg contains the femur, tibia, fibula and foot bones. At the wrist, the ulna is on the little-finger side and the radius is on the thumb side.

Functions of the skeleton

The skeleton has four main functions:

• Support: Helps you stand upright.
• Movement: Bones and muscles work together as the musculoskeletal system. Movable joints allow bones to move relative to one another.
• Protection: The skull protects the brain; the rib cage protects the heart and lungs.
• Shape: Bones help determine body shape, such as the shape of the head.

Bone shape is related to function. Cavities such as the skull cavity protect organs, while projections on bones provide attachment points for muscles and tendons.