A young person's skeleton The 206 bones of the skeleton form a strong, flexible internal framework that supports the rest of the body. The skeleton also gives the body its shape, allows it to move and protects the soft organs inside against injury. Different parts of the skeleton have different roles. The skull, for example, protects the brain and shapes the face. The rib cage surrounds and protects the heart and lungs. The vertebrae of the backbone together provide a strong, flexible support for the body. The long bones of limbs work like levers to move the arms and legs.
An adult human's skeleton is made up of 206 bones. Bones are made from a combination of minerals, such as calcium phosphate, that give them hardness, and tough collagen fibres, that give them strength and some flexibility. Their internal structure makes bones light but strong. Weight for weight, bones are six times stronger than steel. As well as supporting the body, each bone provides anchorage points for the muscles that pull on the skeleton to move the body.
The old bones of a museum skeleton are dry and brittle. But inside a living body, a bone is moist and contains living cells that maintain it. It is neither dry—it contains around 20% water—nor brittle.
Like other body organs, bones have a supply of blood vessels to meet the demands of cells within the bone, along with nerves that carry signals from receptors within the bone.
Bones of an adult skeleton
Bone marrow makes up about 4% of the total body mass of humans.
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