The spine, or backbone, runs from the base of the
skull to the pelvis, serving as a pillar supporting the
body's weight and as protection for the spinal cord. There
are three natural curves in the spine, giving it an "S" shape when
viewed from the side. These curves help the spine withstand great
amounts of stress by providing an even distribution of body
weight.
The spine has three major components: bones, joints, and discs.
It is made up of a series of 24 individual bones called vertebrae
that are stacked to form the spinal column. The spine is divided
into three main sections:
- Cervical spine. The cervical spine is the
uppermost part of the spine, also called the neck. There are seven
vertebrae within the cervical spine. They are numbered C1 to C7,
from top to bottom. The first two vertebrae of the cervical spine
are specialized to allow for neck movement. C1, also called the
atlas, sits between the skull and the rest of the spine. C2, also
called the axis, has a bony projection (odontoid process) that fits
within a hole in the atlas to allow rotation of the neck. The first
spinal curve is located at the cervical spine. It bends slightly
forward, resembling a "C." This forward curve is called a lordotic
curve.
- Thoracic spine. There are 12 vertebrae (T1 to
T12) in the chest section, called the thoracic spine. The ribs
attach to the spine on the thoracic vertebrae, except for the last
two, T11 and T12. The curve of the thoracic spine bends outward
like a reverse "C" and is called a kyphotic curve.
- Lumbar spine. The lumbar spine, or lower back,
usually consists of five vertebrae numbered L1 to L5. (Some people
have six lumbar vertebrae.) The lumbar spine, which connects the
thoracic spine and the pelvis, bears the bulk of the body's
weight. For that reason, the lumbar vertebrae are the largest. The
curve of the lumbar spine also bends forward (lordotic curve).
Below the lumbar spine is a large bone called the sacrum. The
sacrum actually consists of several vertebrae that fuse together
during a baby's development in the womb. The sacrum forms the
base of the spine and the center of the pelvis. The coccyx, or
tailbone, is another specialized bone created by the fusion of
several smaller bones during development.
Vertebrae (bone)
Each vertebra consists of the following parts.
- Body. The body is the front portion and the
main weight-bearing structure of the vertebra.
- Spinous process is the rear portion of the
vertebra. It is the bony ridge you can feel down your back.
- Laminae are two small plates of bone that join
in the back of the vertebra.
- Pedicles are short, thick bumps that project
backward from the upper part of the vertebral body.
- Transverse processes are the bony projections
on either side of the vertebra where the laminae join the pedicles.
Muscles and ligaments attach to the spine on the transverse
processes.
- Facet joints are the spinal joints, the areas
on the spine where one vertebra comes into contact with
another.