Spine

The spine (vertebral column) is a flexible chain of small bones running from the base of the skull to the lower back. Each bone in the spine is called a vertebra. Together they support the body's shape and allow the spine to bend forward, extend backward, and twist sideways.

A long canal runs through the center of the spine, containing the spinal cord—the main pathway transmitting signals between the brain and body. The spine therefore serves two functions: supporting the body and protecting the nervous system.

Sections

The human spine divides into five sections: the cervical (neck) region, the thoracic (upper back) region with ribs attached, the lumbar (lower back) region with larger vertebrae that bear more weight, the sacrum (a fused set of bones), and the coccyx (tailbone). The total number of separate bones is 33 when counting the fused vertebrae, though some may fuse together with age.

Structure of a vertebra

Each vertebra has a short, round body that bears weight and extends into bony projections (processes) where muscles and ligaments attach. Between two adjacent vertebrae sits an intervertebral disc made of a tough outer ring and a soft center; it acts like a shock absorber for the spine.

Lateral shape

Viewed from the side, a normal spine is not straight; it has four natural curves. These curves help distribute weight and maintain body balance when standing. An excessive curve or sideways deviation is recognized as a health condition, such as scoliosis (lateral curvature).