The Human Skeleton

The human skeleton is the framework of bones and cartilage that supports the human body, protects internal organs, and provides the surface to which muscles attach to enable movement. Bones also serve as sites of blood cell production and store minerals such as calcium and phosphorus.

An adult human typically has about 206 bones. A newborn infant has more—roughly 270 bone and cartilage segments—some of which fuse together as the person grows, for example the bones of the skull and those of the lower back.

Major divisions

The skeleton is divided into two parts. The axial skeleton includes the skull, spine, ribcage, and breastbone. The appendicular skeleton includes the bones of the arms, legs, shoulders, and pelvis. The axial skeleton's primary functions are protection and support; the appendicular skeleton is mainly concerned with movement.

Bone structure

Bone is living tissue that is constantly being renewed. It consists of two types: compact bone on the outer surface and spongy bone within. Cells called osteoblasts build new bone, while osteoclasts break down and remove old bone. This balance determines bone strength.

Joints

The point where two bones meet is called a joint. Some joints move freely, such as the elbow, shoulder, and hip; others are immobile, such as the connections between skull bones. Ligaments hold bones together, while tendons attach muscles to bone.

Sex differences and forensic science

The pelvic bones of women are typically wider than those of men, a difference related to childbirth. Because of these differences, experts in osteology and forensic investigation can determine from bones the sex, age, and prior health status of a person.