Your chest cavity is formed by 24 ribs extending from the twelve thoracic vertebrae . The five lumbar vertebrae are the largest and carry most of your body weight. Below your lumbar vertebrae is the sacrum , a single bone consisting of five fused vertebrae. At the base of your spine is the coccyx , or tailbone, which is also formed by fused vertebrae. In between your vertebrae are shock absorbers called discs .
Discs have a stronger outer casing with a pliable jelly-like substance inside.
The top and bottom of the disc is attached firmly to the vertebrae. When a disc is damaged, the jelly-like substance may protrude from between your vertebrae, creating the impression that a disc has moved. Your spinal cord , with your brain, forms your central nervous system. It is approximately 18 inches long and one-half inch thick. Your vertebrae form a canal through which it runs.