Skeletal muscles attach to bones, and when they contract they pull on the bones - causing movement. When your blood supply of calcium runs low, calcium can be reabsorbed from bone tissue. Calcium is needed for proper nervous system function, and is also necessary for the contraction of muscles. Blood cells are formed in the red bone marrow, which is found in the ends of our long bones, and also in flat bones, like the sternum. There is an outer collar of long bone, with spongy bone inside.
Short bones have a thin compact bone outer layer, and are filled with spongy bone.
The number of sesamoid bones varies from person to person. Your skull bones, sternum, and ribs are flat bones. These bones have 2 plates of compact bone with a layer of spongy bone inside. Examples are some of the skull bones, the vertebrae, and hip bones. The epiphyseal plate remains throughout childhood and into adolescence.