Sandwiched between each vertebra are spongy but tough cushions called discs, which act as shock absorbers for the vertebrae, and give the spine its flexibility. Strong elastic ligaments hold all the vertebrae and discs firmly together in a column. Muscles are attached to the vertebrae by rubbery connections called tendons, and the contractions and expansions of the complex layers of back muscles produce the movements of your back and your upper body. The spine also provides a protective case for the spinal cord, which runs from the base of the brain into a hollow canal down the vertebrae. This is the main communications cable between the brain and the rest of the body, and nerves from the spinal cord branch out and leave the spine through spaces between the vertebrae.
Doctors divide the back into the five regions shown in the diagram.
It is the lumbar region, right at the bottom of the flexible part of the back, and just above the pelvis, where back pain strikes most often. This is because the lower part of the back bears the entire weight of the upper body, plus any weight the person is carrying. It also twists and bends more than the upper part of the back. The commonest causes of back pain Most back pain is caused not by serious damage or disease but by sprains, strains and minor injuries. This is often called 'simple back pain' by doctors.