Back Anatomy and Physiology

Whether the human body is propelled forward, backward, upward, or downward, the back is an essential component of every movement. The back is a complex structure, part rigid support and a protective, bony sheath, part intricate musculoskeletal device capable of both bearing significant forces, as well as flexing and extending through a remarkable range of movements.

The back consists of the entire posterior, or rear, of the body from the neck to the buttocks. The back and its characteristics are best understood through an appreciation of each of its components. The spine, or backbone, is the bony structure that is divided into four separate regions: cervical spine, thoracic spine, lumbar spine, and sacral spine.

The cervical spine comprises seven vertebrae referenced as C1 through C7, with C1 at the top of the spine. The cervical spine has three essential skeletal functions: it supports the weight of the skull; vertebrae C1 and C2 are the structures responsible for the neck and head being able to turn; and vertebrae C6 and C7 permit the flexion and extension of the neck and head. The thoracic spine is made up of 12 vertebrae (T1 through T12). This structure is capable of very little motion, as it is primarily protective. The lumbar spine, commonly referred to as the lower back, is responsible for the support of the torso when the body is upright, and to bend, extend, and rotate at the waist when the body moves accordingly. The lumbar structures are the most stressed and the most injured of any portion of the back. The sacral spine is the base of the spine that connects the spine to the pelvis. Its chief components are the sacroiliac bone and the coccyx, or tail bone.

Other components of the spine include the vertebrae, the small ring-shaped bones that form the spine. The spinal column is the collection of vertebrae forming the backbone. The disks are sacs filled with a cushioning liquid that rest between each vertebra to absorb shocks to the spine. Without the disks, the vertebrae would rub and grate on another, and the spine would not be capable of a smooth, efficient range of motion. The spinal cord, which is the vital nerve structure running from the brain inside the spinal cord, is protected by the spinal column; the cord is subdivided into nerve roots that radiate into the body. The neural foramina are the openings in the spinal column for the nerve roots to branch out into the torso. Facets are the joints that hold the vertebrae together, both for the stability of the spine and to permit movement. The ligaments, tendons, and muscles stabilize the spinal column. Finally, there is the sciatic nerve, the most prominent of the nerves radiating from the nerve roots into the buttocks, below the sacral spine.

The muscles that are critical to the proper movement of the spine are divided into three types: extensors, flexors, and oblique. The extensors are large muscle structures located on the posterior of the spine. The primary purposes of the extensors are to support the back when the body is in an upright position and to provide support and stability to acts of lifting. Weightlifters, for example, pay particular attention to the development of these muscles. The erector spinae, a pair of muscles set on either side of the lumbar spine, and the gluteal muscles, located in the buttocks and upper thighs, are the most prominent of the extensors.

The flexors are the muscles located on the anterior (front) of the spine. These muscles permit the body to flex in all directions, with particular importance to the motions of bending forward, lifting, and the arching of the lumbar (low back) spine. The flexor muscles include the abdominal muscles.

The oblique muscles are on the medial, or middle, of the spine. These muscles are necessary in the rotation of the spine as well as in the maintenance of proper posture.

Optimum back health is impacted upon by a variety of factors. Poor general fitness will often place undue stress on the back in daily living, stresses that become even more pronounced when the body is subjected to the stress of athletic competition. Poor posture and the repetitive strain of a number of movements, such as twisting, turning, or lifting, all may place stress on the back structure, particularly the weight-supporting lumbar area.

Age is a factor in the preservation of good back health. Muscles will naturally weaken with age. A failure to exercise all back muscle groups, or the creation of imbalances in the back muscles, will place stresses upon the back muscles that may pose long-term problems.

SEE ALSO Back injuries; Bone, ligaments, tendons; Skeletal muscle.