Spine is the part of the skeleton that extends down the center of the back. It is made up of a column of bones called vertebrae. The spine plays an important role in posture and movement, and it also protects the spinal cord. The spine is also called the spinal column, vertebral column, or backbone. Animals with a spine are called vertebrates.
The human spine consists of 33 vertebrae, but some of them grow together in adults. There are 7 cervical (neck), 12 thoracic (chest), 5 lumbar (lower back), 5 sacral (hip region), and 4 coccygeal (tailbone region) vertebrae. The vertebrae are held in place by muscles and strong connective tissue called ligaments. Most vertebrae have fibrous intervertebral disks (also spelled discs) between them to absorb shock and enable the spine to bend.
The spine normally has a slight curve. Abnormal curvatures may be present at birth. They may also result from disease, poor posture, or a strain on the muscles attached to the spine. Scoliosis occurs when the spine curves sideways. Kyphosis, or hunchback, is a forward bending of the thoracic vertebrae that often affects elderly people. Lordosis, or swayback, is an exaggerated curvature of the lumbar vertebrae.
Fractured cervical vertebrae may injure the spinal cord, resulting in a loss of sensation, paralysis, or even death. Whiplash is an injury to the muscles and ligaments attached to cervical vertebrae. It occurs when a sudden force—such as a rear-end car accident—throws the head backward. As people age, the inner part of an intervertebral disk may stick out through the outer part. This condition is called a disk herniation. Arthritis and degeneration (breakdown) of intervertebral disks may cause low back pain. Nerve compression from a herniated disk or other conditions may cause sciatica (pain shooting down the leg).
