The control center of the body is the brain and its extension, the spinal cord. Every organ of the body is controlled by the brain and the nerves which extend out of the spinal cord. Because the brain and spinal cord are so important to the functioning of the body, they are housed in special protective structures. The brain is protected by the skull, and the spinal cord is protected by the spinal column. The spinal column is composed of 26 moveable segments, of which 24 are vertebrae (a single one is called a vertebra). These vertebrae are moveable, so that we are able to bend and twist. Between each vertebra is (a gelatinous-filled fibrous cartilage) cushion, called a disc. The vertebrae are supported in position by means of muscles and ligaments. In addition, there are three normal curves in the spinal structure: at the neck, at the mid-back, and at the low back. These normal curves provide the body with extra support, and acts as a shock-absorber. When the body suffers a trauma or stress, either emotional or physical, the ligaments may stretch, or the muscles may tense up and go into spasm, pulling on the spinal cord segments, or vertebrae, and cause them to move out of place. When the vertebrae are moved out of place, they will exert pressure on that area of the spinal cord. Just as a garden hose will not allow a normal amount of water to flow through if it is being stepped on, a compressed or irritated nerve will not enervate the organ of the body which it controls with the same intensity as a nerve which is free from interference. A severely compromised spinal structure may also exert so much pressure on the disc that the disc ruptures or herniates. The condition of a vertebra which is compressed, either slightly or more severely in the manner described above, is called a "Subluxation".