Earth Science: Biology – Humans – Skeletal system: Bones
Humans have a bony skeleton with movable joints. Several key adaptations provide strength and flexibility and enable human beings
to walk upright.
The adult human skeleton has about 206 individual bones and several important functions. It supports the body and protects the inner organs. For example, the skull encases the brain and protects it from bumps and minor injuries; the rib cage protects the heart and lungs.
Using the joints in the skeleton, muscles attached to individual bones and cartilage can contract and relax to move the body. The main body axis, or axial skeleton, consists of the skull and vertebral column. Attached to the vertebral column are the arm and leg bones (the appendicular skeleton) and the shoulder and hip (pelvic) girdles.
The vertebral column, with its S-curve structure, can absorb a great deal of sudden and heavy force while providing the support required for an upright posture.
Vertebral column
The human backbone, or vertebral column, consists of 33 vertebrae, each separated by spinal discs. The discs are made of cartilage and have a jellylike center allowing them to absorb shocks during walking, running, jumping, and other physical activity.
The spinal cord—central axis of the nervous system-runs through a canal within the vertebral column. The spinal cord distributes signals between the brain and the individual organs in the body.
An injury to the spinal cord, such as a broken vertebra or a ruptured disc, can damage the spinal cord and cause temporary or permanent paralysis.
Bones
The bones of humans and other mammals consist primarily of calcium phosphate. They are covered with a thin layer of connective tissue called the periosteum and have a compact outer layer and spongy inner scaffolding. Bone marrow is distributed on the inner scaffolding and laced with blood vessels.
Red and white blood cells and platelets are formed in the marrow. The long bones in the thighs, shins, and arms differ from the flat bones that form the skull and ribs. However, all bones constantly reconstruct themselves. Thus, they can repair themselves after a break.
X-RAY TECHNOLOGY
While experimenting with cathode rays, W. C. Rontgen discovered an un- known form of radiation and named them x-rays. This revolutionized medical diagnostics and its potential in human medicine. Today, x-rays are a standard practice in medical diagnostics.
Mammography and computerized tomography (CT) are specialized methods. Other scientific areas also take advantage of x-ray technology. Archaeology and art history, for example, rely on this technique to analyze specimens.