The Anatomy Of Your Back: Back Pain

Content provided by the Faculty of the Harvard Medical School

The anatomy of your back

The human spine consists primarily of a line of interlocking bones called vertebrae (derived from the Latin term vertere, meaning "to turn"). Each vertebra has a roughly cylindrical body with a bony ring attached to its back surface (see Figure 1). Projections called processes extend in several directions from this ring. Vertebrae are stacked on top of each other, and are linked together by ligaments to form joints that permit a small amount of forward, backward, and side-to-side bending, as well as some twisting and up-and-down movement.

Figure 1: A closer look at your lumbar vertebrae A. Each vertebra has a cylindrical body with a bony ring attached to its back surface as well as processes that project out in different directions from this ring. Intervertebral disks, tucked between each pair of vertebrae, serve as shock absorbers. B. Each intervertebral disk has a gelatinous central part, called the nucleus pulposus, and a fibrous covering, called the annulus fibrosus. Each vertebra normally has seven processes (two are obscured in this illustration), which help stabilize your spine.

The lower or lumbar spine (see Figure 2) consists of the lowest five vertebrae. It extends from the bottom of the rib cage to the sacrum (the large triangular bone found between your hipbones) and connects your upper and lower body. Lumbus, the Latin word for loin, is the root of the word lumbar and also of lumbago, a general term doctors often use to describe low back pain caused by sprain or strain of unknown origin. Your lumbar spine's strength and flexibility allow you to twist, turn, bend, stand, walk, run, and lift. The part of the spine also supports most of your body's weight and is subjected to great stress when you perform normal daily activities. Some actions, such as lifting or carrying heavy weights, can exert extreme forces on the lumbar spine. In many people, this type of high stress contributes to an aching back.

Figure 2: Regions of the spine Your spine is divided into three regions: the cervical, the thoracic, and the lumbar. Low back pain originates in the lumbar area, which extends from the bottom of your rib cage to your sacrum (the triangular bone found between your hipbones) and includes the lowest five mobile vertebrae.

Last updated:	January 23, 2007