The skeletal system and the muscular system work together in a complementary fashion to make movement possible. Neither system would be effective without the other. Bones of the skeletal system provide a strong framework for the muscles that are attached to them. When the muscles contract and relax in different combinations, they create a pulling effect on the bones that results in movement.
Structures of the skeletal system include bones, tendons, and ligaments (Fig. 13-1). Bones are composed of dense connective tissue, which includes bone cells in a matrix of the mineral calcium and collagen fibers. Bones are dynamic, living, ever-changing structures. Unlike the white, dry, dead bones you may have seen, living bones have a rich supply of blood vessels and nerves. If injured, they may hurt and bleed. The most common injuries to bones are fractures. This also means they have the ability to heal themselves. Important to the healing process is the development of osteocytes, new bone cells, which are constantly created through osteogenesis. New cells replace older ones that are injured or broken down as they age. Because bones are able to remodel themselves in this way, certain activities, such as weight lifting or weight-bearing exercise like jogging and walking, stimulate bones to become stronger and denser.
Stresses on bone, such as weight bearing and muscle contractions, help bones to remain strong or become stronger.
The skeletal system provides protection, movement, and a framework for the body. Bones that provide protection include those that make up the cranium; they are fused together to create a strong container for the brain. Other protective bones include those of the vertebral column, which protect the spinal cord and combine with the sternum and ribs to create the thorax, which protects the heart, great vessels, and lungs (Fig. 13-2).
The skeletal system also plays important roles in blood production and mineral regulation. Marrow, a soft substance within bone, performs hematopoiesis, or the production of red and white blood cells. This explains why a bone marrow transplant may be necessary for someone with a blood disorder such as leukemia.
Learning Style Tip
Rewrite explanations, concepts, and definitions from this chapter in your own words. This forces you to think about what they really mean and to put them into simpler terms that you will remember. For verbal and auditory benefit, read your notes aloud and record your voice. This will enable you to study while you are driving or exercising.
Bones store essential minerals such as calcium, phosphorus, and ...