Anatomy of the Back


Maj Spencer
The back is one of the strongest parts of the body, and it’s made up of bones, muscles, nerves, and ligaments. Dr. Patel, can you help us understand the anatomy of the back?

Dr. Patel
Of course, Major Spencer. Any anatomy lesson about the back must start with the spine. The spine, which begins at the neck and runs down to the tailbone, provides the main support for the body. A healthy adult spine has a natural S-shaped curve when viewed from the side. Strong back muscles stabilize the spine and help to keep the spine’s curves in their natural alignment.

There are two main muscle groups that affect the spine: extensors and flexors. Extensor muscles are attached to the back of the spine and enable us to stand up and lift things. Flexor muscles, which include the abdominal muscles, are in the front. They give us the ability to bend forward, or flex, and play an important part in controlling the arch in the lower back.

Blocks of bone, called vertebrae, interlock with each other to form the spinal column. There are 33 individual vertebrae, and they are numbered and divided into five regions: cervical, thoracic, lumbar, sacrum, and coccyx. The lumbar region is in the lower back, and its main function is to bear the weight of the body. The five lumbar vertebrae, which are larger than the other vertebrae, are numbered from the top down, L1 to L5.

Between the vertebrae are intervertebral discs. These discs are tough, flexible shock absorbers that keep the bones of the vertebrae from rubbing together. They act like coiled springs, allowing range of motion and helping the body to maintain balance.

At the back of each vertebra are bony projections that form the vertebral arch. Together, the vertebral arches form a hollow canal, called the spinal canal, which protects the spinal cord. The spinal cord is about 18 inches long and runs from the brainstem to the L1 vertebra. It is the body’s information super-highway, carrying messages between the brain and the rest of the body. Nerves branch off from the spinal cord between each vertebra and go to all parts of the body.

Finally, strong bands of tissue known as ligaments and tendons help to hold the bones of your spine in place, protect the intervertebral discs, and attach the large muscles of your back to the vertebrae.