Skeletal System

The body’s internal framework — 206 bones in a typical adult, plus the cartilage and joints that connect them.

Main parts

• Axial skeleton — the skull, spine, and ribcage; the body’s core.
• Appendicular skeleton — the limbs and the girdles that attach them.
• Bone tissue — the living hard tissue that bones are made of.
• Cartilage — firm, flexible padding and structural support.
• Joints — where bones meet; they determine movement.
• Ligaments — tough bands tying bone to bone.

What it does

• Support and shape — holds the body up and gives it form.
• Protection — the skull shields the brain; the ribcage shields the heart and lungs.
• Movement — bones act as levers for muscles to pull on.
• Blood production — bone marrow manufactures red and white blood cells.
• Storage — bone is the body’s reservoir of calcium and phosphate.

Key idea

Bone is living, changing tissue — continually broken down and rebuilt, so the skeleton you have is never quite the one you had a year ago.