Skeletal System

Almost everyone has learned at one point or another that there are 206 bones in the human body. And almost everyone has broken or fractured their arms or legs.

The 206 bones in an adult human provide the body with shape, work with the muscles to allow movement, supply a place in which to produce numberous cells, and protect the delicate internal organs. There are a number of bones that have specific purposes: the skull, for example, protects the brain, and the rib cage protects the heart and lungs.

The place where two or more bones meet is called a joint, of which there are two types: movable joints and fixed joints. Fixed joints do not allow movement and exist mainly in the skull where a number of bony plates are fused together. There are two subtypes of movable joints: hinge joints and ball and socket joints, both of which are held together by tissues called ligaments. Hinge joints function like a door hinge; they allow the two bones to bend up to 180 degrees. Ball and socket joints are composed of one bone that is rounded at one end and another bone that has a cup shaped hollow. The rounded bone fits into the hollow and is held in place by a ligament; this allows an almost 360 range of movement.

Bone tissue also contains a number of cells that the body relies on to keep healthy. The bone marrow produces all new blood cells and releases them into the bloodstream: red blood cells carry oxygen, white blood cells fight infection, and platelets help the blood clot.

The different bones in the skeleton are: the cranium, the mandible, the lavicles (2), the scapulas (2), the sternum, the ribs(many), the floating ribs (2), the humerus' (2), the ulnas (2), the radii (2), the carpals (many), the metacarpals (10), the phalanges (40- there are phalanges on both feet and hands), the vertebral column (made up of many vertebrae), the pelvis, the sacrum, the femurs (2), the patellas (2), the fibulas (2), the tibias (2), the tarsals (many), and the metatarsals (10).