The skeletal system consists of bones, cartilage, and the membranes that line the bones. Each bone is an organ that includes connective tissue (bone, blood, cartilage, adipose tissue, and fibrous connective tissue), nervous tissue, and muscle and epithelial tissues (within the blood vessels). Bones have many functions, including Support. Bones provide a framework for the attachment of muscles and other tissues. Protection. Bones such as the skull and rib cage protect internal organs from injury. Movement. Bones enable body movements by acting as levers and points of attachment for muscles. Mineral storage. Bones serve as a reservoir for calcium and phosphorus, essential minerals for various cellular activities throughout the body. Blood cell production. The production of blood cells, or hematopoiesis, occurs in the red marrow found within the cavities of certain bones. Energy storage. Lipids (fats) stored in adipose cells of the yellow marrow serve as an energy reservoir.