THE HUMAN SKELETON
The human skeleton consists of 206 bones, most of which are paired (left and right) or grouped by area (the skull or the spine, for example), as shown in Figure 1.
FIGURE 1 The human skeleton consists of 206 bones that are paired or grouped by area.
FIGURE 1—cont’d
Bone may seem like a “dead” material because it is so hard and inflexible. In reality, the skeleton is a very active organ system that can repair itself and alter its form over time. Bone, as a tissue and a structure, responds to the stresses placed on it, adding or subtracting boney material as needed. This activity that takes place throughout our lives, plus the genetic potential we inherit from our parents, results in the biological and anatomical variation we see between and within populations and individuals. Bones perform four main functions for the body: support, motion, protection, and growth. First, the skeleton provides the infrastructure for attachment and support of the softer tissues in our bodies. Second, these attachments allow the bones to act as levers, providing motion, powered by muscles, at the joints. The structure and arrangement of our bones sets the range of motion for our limbs and bodies. Third, the hard bones protect our soft organs from physical damage; this is especially true of the brain (encased by the skull) and the heart and lungs (enclosed within the spine and rib cage). Fourth and finally, the bones are centers of growth from infancy to early adulthood; they also continue important physiological functions throughout our lives by housing the tissue that makes red blood cells. Bones supply us with a ready source of calcium if our dietary intake of that mineral is too low for a too long period.
