University of Wisconsin Interventional Pain Program

Understanding The Spine

The spine is made up of a column of bones (vertebrae) alternating with discs. The vertebrae provide structure and support for the body and protect the spinal cord. The discs act as shock absorbers. Muscles and ligaments attach to the spine to help to provide extra support and protection for the spine and spinal cord. Knowing how these structures work can help you understand your spine and why your doctors may feel your pain is spine-related.

The Bones and Joints:

There are 33 vertebrae that make up the spine: 7 in the neck (cervical), 12 in the upper back (thoracic), 5 in the waist/lower back (lumbar), and 9 in the tailbone. The vertebrae of the tailbone are joined together to form the sacrum and coccyx. The sacrum is joined to the pelvis by the sacrociliac joints. There are 2 sacroiliac joints: one on the left side and one on the right side.
All vertebrae are named and numbered according to their location. For example: the first vertebra in the low back is called L1 for lumbar vertebra number 1. The second vertebra in the low back would be L2, and so on. The ribs are attached to the thoracic vertebrae.

Each vertebra is made up of a body attached to an arch. The vertebral body is a solid mass of bone. The bony arch is attached to the back of the vertebral body and makes up the side and back of the vertebra. The vertebrae all fit together perfectly, one on top of another. The vertebral bodies are separated by discs for cushioning, while the arches of the vertebrae meet to form joints. The joints where the vertebral arches meet are called facet joints. They help the spine to twist and bend as you move. Facet joints are a common source of back pain.
The bones and joints of the spine are responsible for supporting the weight of the body. The vertebrae of the low back are responsible for supporting more weight than the vertebrae in the neck. This is why the vertebrae get larger as you move from neck to low back.

The Discs:

The discs are attached to the bodies of the vertebrae. They separate the vertebral bodies and act as shock absorbers. The discs are made of a soft jelly-filled core surrounded by a thick fibrous shell. The discs are named and numbered according to which vertebrae they sit between. For example: the disc between the L4 and L5 vertebrae is called the L4-L5 disc. Many different problems can happen with discs. Thus, discs are a common source of back pain. Your doctor can tell you more about your specific discs and whether or not they may be causing pain.

The Spinal Canal:

The bony arch and body of the vertebrae make a central canal for the spinal cord. This canal is surrounded by bone. It is called the spinal canal. It houses the spinal cord and branches off the spinal cord called the spinal nerves.
The spinal cord and spinal nerves are protected from injury by several layers of cushioning. Directly inside the bone of the spinal canal is a layer of fat and blood vessels. This is called the epidural space. Sometimes medications are injected in the epidural space to decrease pain. Beyond the epidural space is the dura, or sac that contains the spinal cord and spinal nerves. The sac is filled with clear watery fluid that surrounds the spinal cord. This fluid is called CSF. This is the fluid that is obtained in a lumbar puncture or “spinal tap.”

The spinal nerves exit the spinal canal through special gaps in the bone. These special gaps lie between 2 adjacent vertebrae. Spinal nerves exit the spinal canal on both the left and right sides of the body. Each spinal nerve controls a specific area of the body. The spinal nerves are named and numbered according to their location, level, and side of the body. For example: the nerve exiting the spinal canal below the L5 vertebra on the left side of the body would be the left L5 spinal nerve.

Your doctor can tell you more about your specific nerves and whether or not they may be a source of your pain.

Ligaments and Muscles:

Ligaments and muscles tightly bind all of the components of the spine together to provide stabilization and flexibility. Major muscle groups for the entire body attach to the spine. Injury to one or more of the components of the spine can cause muscle spasm and pain. Physical therapy helps to strengthen muscles used in keeping the spine strong, stable, and flexible. Your doctor can tell you more about your specific ligaments and muscles and whether or not they may be contributing to your pain.