Bones, Muscles, and Joints (page 2) Every time you walk, settle
into a chair, or hug your child, you're using your bones,
muscles, and joints. Without these important body parts, we
wouldn't be able to stand, walk, run, or even sit. Bones and
What They Do From our head to our toes, bones provide support
for our bodies and help form our shape. The skull protects the
brain and forms the shape of our face. The spinal cord, a
pathway for messages between the brain and the body, is
protected by the backbone, or spinal column. The ribs form a
cage that shelters the heart, lungs, liver, and spleen, and the
pelvis helps protect the bladder, intestines, and in women, the
reproductive organs. Although they're very light, bones are
strong enough to support our entire weight. The human skeleton
has 206 bones, which begin to develop before birth. When the
skeleton first forms, it is made of flexible cartilage, but
within a few weeks it begins the process of ossification.
Ossification is when the cartilage is replaced by h