The human spine consists of 33 vertebrae, but some of them grow
together in adults. There are 7 cervical (neck), 12 thoracic (chest region),
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
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. It usually affects overweight
people and pregnant women.
Damage to the spine often occurs in the cervical and lumbar
regions. 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 is likely to stick
out through the outer part. This is called a slipped disk. A slipped disk
in the lower back may pinch nerves, causing lumbago (low back pain) or sciatica
(pain shooting down the leg).