Spine Anatomy and Physiology
The spine consists of 24 small bones called articulated vertebrae, and nine fused vertebrae in the sacrum and coccyx. Your spine is one of the most important parts of your body. It provides you the structure and support to keep your body upright, and facilitates bending and general movement with great flexibility. Most importantly, the spine protects your spinal cord from trauma or injury.
The spinal cord is a column of bundled nerves that connects your brain to the rest of your body. It transfers the motor and sensory commands necessary for your body’s responses to external stimuli such as pain or temperature change. The spinal cord also allows you to control body movements.
Within the spinal cord are vertebral segments, groups of small cylindrical bones called vertebrae. Between each individual vertebra is a soft, gel-like cushion called an intervertebral disc These discs act as shock absorbers and prevent the vertebrae from rubbing together. Each disc also forms a symphysis (fibrocartilaginous joint), which acts as a ligament to hold together multiple vertebrae and facilitate movement between individual vertebra.
Intervertebral discs are composed of two main parts: a tough outer layer called the annulus fibrosis, and a gel-like inner layer called the nucleus pulposus. The annulus fibrosis consists of interwoven ligament fibers designed to ensure spinal vertebrae are securely connected. The nucleus pulposus, however, is mostly water and made of proteoglycans (gel-like proteins) that absorb and cushion most of your movements.
Your discs are made up of about 80 percent water. As you get older, they begin to slowly lose this fluid, which causes them to shrink and lose their shock-absorbing abilities. As discs degenerate, small tears occur in the outer layers. These tears then allow some of the gel-like inner layer to bulge out of the disk and touch neighboring nerves (disc herniation). Due to this gel-like material containing many inflammatory proteins that can inflame the nerves, this results in pain, tingling sensations, numbness, and weakness in your external extremities. In some cases, disc herniation may affect your spinal cord and cause weakness in your lower extremities.