Understanding How the Back Works
Key points
- The spine, which connects the skull to the pelvis, is also called the vertebral column.
- Between each vertebra are spongy pads, like soft cushions, called discs - or more correctly, intervertebral discs.
- The nerves that come off the spinal cord are called nerve roots.
- There are a series of ligaments that are important to the stability of the vertebral column.
The spine, which connects the skull to the pelvis, is also called the vertebral column. It consists of 24 segments of block-shaped bone called vertebrae and an additional 9 fused vertebrae that make up the lowest part of the spine, the sacrum and tailbone. Each vertebrae of the vertebral column has protruding bony areas for the attachment of muscles that are important for the spine to move. The spinal column protects the spinal cord and its emerging nerves that run down most of the length of the spine.
The vertebrae have two major functions:
- To bear the weight of the body
- To house the spinal cord or spinal nerve roots (cauda equina) within the spinal column
The spine is arranged in three natural curves:
- The neck region or cervical spine, made up of 7 vertebrae - where the vertebrae curve forward.
- The trunk region or thoracic spine, made up of 12 vertebrae - where the vertebral column curves backward, and to which the ribs attach
- The low back region or lumbar spine, made up of 5 vertebrae - which curves forward in the same direction as the cervical spine.
When these curves are in their normal alignment, the body is in a balanced position. This distributes weight evenly throughout the vertebrae so one is in a less vulnerable position for strain and injury.
There are two major parts to each vertebra:
- Vertebral body - The vertebral body is the front portion of the vertebrae. It is shaped like a cylinder and is greater in height than the back portion.
- Vertebral arch - The vertebral arch is the back portion of the vertebrae. It is an irregularly shaped structure.
At the center of each vertebra is a hole, protected by the surrounding strong bone. Placed together, the central opening of each vertebra makes up the spinal canal through which the spinal cord, cauda equina, or spinal nerve roots pass. The spinal cord is the mass of nerve that connect the brain to the rest of the body.
Each vertebra has important bony projections called processes that provide sites for the attachment of ligaments and muscles that are important for the stability and movement of the spine.
- The projections on either side of each vertebra are called transverse processes, and the ones at the back are called the spinous processes. The transverse processes are long and slender; the spinous processes are broad and thick.
Written and revised by
David Cohen, M.D.
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