David gets wrapped up in a cast to learn about broken bones. The human skeletal system is designed to support the human body, offer it protection, and provide a means of locomotion. Bone is the essential framework to which muscles are attached.
Bone is constructed in layers.
The outside layer is known as the periosteum. This is where blood vessels and nerve cells are located. The next layer is the compact bone. This area has collagen and crystals of calcium and phosphorus. The next layer is of spongy bone, with shock-absorber qualities.