The human skeletal system

The skeletal system is the framework of bones and connective tissue that gives the human body its shape, supports its weight and protects its internal organs. An adult skeleton is usually described as having 206 bones, although the number is higher at birth because some bones fuse together during growth. Bone is a living tissue, hard and mineralised on the outside but containing marrow that produces blood cells, and it also serves as the body's main store of calcium.

Anatomists divide the skeleton into two parts. The axial skeleton forms the central core and includes the skull, the vertebral column and the rib cage. The skull protects the brain and houses the organs of sight, hearing, smell and taste, while the vertebral column, made up of a stacked series of vertebrae, supports the trunk and shields the spinal cord. The rib cage surrounds and protects the heart and lungs. The appendicular skeleton comprises the limbs and the girdles that attach them to the axial skeleton: the shoulder girdle, the arms, hands and wrists, the pelvic girdle, and the legs, knees and feet.

Bones meet at joints, which determine how the body can move. Some joints, such as those between skull bones, are essentially fixed, while others, including the knee, shoulder and wrist, allow a wide range of motion. Movable joints are held together by ligaments and cushioned by cartilage, and they are moved by muscles attached to the bones by tendons. The study of bones and the skeleton is known as osteology. Together the bones, joints and supporting tissues provide structure, enable movement and protect the body's most vital organs.

Frequently asked questions

How many bones are in the adult human body?

An adult skeleton is generally counted as having 206 bones. Newborns have more, because several bones fuse together as a person grows.

What is the difference between the axial and appendicular skeleton?

The axial skeleton is the central core — skull, spine and rib cage — while the appendicular skeleton is the limbs and the girdles that connect them to the core.

What holds bones together at a joint?

Ligaments connect bone to bone at a joint, cartilage cushions the contact surfaces, and tendons attach the muscles that move the bones.