The spine is composed of 33 interlocking bones called
lumbosacral region of the spine (or lumbar spine)
consists of 5 lumbar vertebrae and 5 sacral vertebrae. The sacral vertebrae,
which are fused together, are called the sacrum.
- The lumbar vertebrae of the spine extend from the
bottom of the rib cage to the sacrum.
- The fifth lumbar vertebra is
connected to the sacrum. The sacrum is connected to the pelvic bones and the
- Because this part of the spine bears the weight
and stress of the trunk and upper body, the lumbar vertebrae are larger and
thicker than those in any other part of the spine.
A disc is located between each pair of lumbar vertebrae. The discs
are capsules of connective tissue with a soft, jellylike center. The discs
absorb shock and make the spine flexible. The bones of the sacrum are joined to
one another and have no discs between them.
The vertebrae are supported by ropy tissues called
ligaments and groups of muscles:
- Abdominal (belly) muscles support the spine from the
front and sides of the body.
- Iliopsoas muscles support the spine
and flex the hips.
- Erector spinae muscles support the back of the
trunk and spine and are the major stabilizers of the spine during
The spinal cord runs through the spinal canal, a tunnel that is
formed by the holes in the center of each of the vertebrae. Nerves branch from
the spinal cord, pass through openings (foraminae) between the vertebrae, and
branch to the lower body.