The spine, or backbone, runs from the base of the skull to the pelvis, serving as a pillar supporting the body’s weight and as protection for the spinal cord. There are three natural curves in the spine, giving it an "S" shape when viewed from the side. These curves help the spine withstand great amounts of stress by providing an even distribution of body weight.
The spine has three major components: bones, joints, and discs. It is made up of a series of 24 individual bones called vertebrae that are stacked to form the spinal column. The spine is divided into three main sections:
The cervical spine is the uppermost part of the spine, also called the neck. There are seven vertebrae within the cervical spine. They are numbered C1 to C7, from top to bottom. The first two vertebrae of the cervical spine are specialized to allow for neck movement. C1, also called the atlas, sits between the skull and the rest of the spine. C2, also called the axis, has a bony projection (odontoid process) that fits within a hole in the atlas to allow rotation of the neck. The first spinal curve is located at the cervical spine. It bends slightly forward, resembling a "C." This forward curve is called a lordotic curve.
There are 12 vertebrae (T1 to T12) in the chest section, called the thoracic spine. The ribs attach to the spine on the thoracic vertebrae in back and wrap around to attach to the breastbone called the sternum in the front, except for the last two, T11 and T12. The curve of the thoracic spine bends outward like a reverse "C" and is called a kyphotic curve.
The lumbar spine, or lower back, usually consists of five vertebrae numbered L1 to L5. (Some people have six lumbar vertebrae.) The lumbar spine, which connects the thoracic spine and the pelvis, bears the bulk of the body’s weight. For that reason, the lumbar vertebrae are the largest. The curve of the lumbar spine also bends forward (lordotic curve).
Below the lumbar spine is a large bone called the sacrum. The sacrum actually consists of several vertebrae that fuse together during a baby’s development in the womb. The sacrum forms the base of the spine and the center of the pelvis. The coccyx, or tailbone, is another specialized bone created by the fusion of several smaller bones during development.
Each vertebra consists of the following parts.
- Body. The body is the front portion and the main weight-bearing structure of the vertebra.
- Spinous process is the rear portion of the vertebra. It is the bony ridge you can feel down your back.
- Laminae are two small plates of bone that join in the back of the vertebra.
- Pedicles are short, thick bumps that project backward from the upper part of the vertebral body.
- Transverse processes are the bony projections on either side of the vertebra where the laminae join the pedicles. Muscles and ligaments attach to the spine on the transverse processes.
- Facet joints are the spinal joints, the areas on the spine where one vertebra comes into contact with another.
In the center of each vertebra is a large opening, called the spinal canal, through which the spinal cord and nerves pass. The vertebrae are held together by groups of ligaments, fibrous tissues that connect bone to bone.
A joint is the area where two or more bones connect. Joints allow for movement, since bones themselves are too hard to bend without being damaged. Facet joints are the specialized joints that connect the vertebrae. The facet joints allow the vertebrae to move against each other, providing stability and flexibility. These joints allow us to twist, to bend forward and backward and from side to side.
Each vertebra has two sets of facet joints. One pair faces upward to connect with the vertebra above and the other pair faces downward to join with the vertebra below.
Intervertebral discs are flat, round cushioning pads that sit between the vertebrae (inter means "between" or "within") and act as shock absorbers. Each intervertebral disc is made of very strong tissue, with a soft, gel-like center, called the nucleus pulposus, surrounded by a tough outer layer called the annulus. When a disc herniates, some of the soft nucleus pulposus may bulge or even protrude through a tear in the annulus. This bulging of the nucleus pulposus can result in pain when the nucleus pulposus puts pressure on nerves.
The spinal cord, the column of nerve fibers responsible for sending and receiving messages from the brain, runs through the spinal canal. It is through the spinal cord and its branching nerves that the brain influences the rest of the body, controlling movement and organ function.
As the spinal cord runs through the spinal canal, it branches off into 31 pairs of nerve roots, which then branch out into nerves that travel to the rest of the body. The nerve roots leave the spinal cord through openings called neural foramen, which are found between the vertebrae on both sides of the spine. The nerves of the cervical spine control the upper chest and arms. The nerves of the thoracic spine control the chest and abdomen, and the nerves of the lumbar spine control the legs, bowel, and bladder.
- Engstrom JW, Deyo RA. Chapter 15. Back and Neck Pain. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, eds. Harrison's Principles of Internal Medicine. 18th ed. New York: McGraw-Hill; 2012. www.accessmedicine.com. Accessed 5/14/2013.
- North American Spine Society. Anatomy of the Spine. Accessed 5/14/2013.
- The Spinal Research Foundation. Learn: Your Spine. Accessed 5/14/2013.
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 5/13/2013..index#11671