What is the periosteum?

• A. Soft inner marrow
• B. Outer membrane covering the bone
• C. Dense cortical layer
• D. Spongy interior

Answer: (B)

The periosteum is the outer membrane that covers the bone. It’s a tough, fibrous layer that coats the bone’s surface (except at joint cartilage). It has two parts: an outer fibrous layer that helps attach tendons and ligaments, and an inner cellular layer with osteoblasts and other cells that can grow or repair bone. This membrane provides blood vessels and nerves to the bone, supports growth in thickness, and aids in healing after injury. It is not the soft inner marrow, the dense cortical shell itself, or the spongy interior.