The
spinal column is made up of bones called vertebrae. The spinal cord runs down your back through your
vertebrae.
The spinal cord carries messages from all of the other nerves that branch
out from it. The spinal cord is located in the vertebral foramen and is made up
of 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal.
Although the spinal column is somewhat flexible, some of the vertebrae in
the lower parts of the spinal column become fused.
The
spinal cord is about 45 cm long in men and 43 cm long in women. However, this is
much shorter than the length of the bony spinal column. In fact, the spinal cord
extends down to only the last of the thoracic vertebrae. Therefore, nerves that
branch from the spinal cord from the lumbar and sacral levels must run in the
vertebral canal for a some distance before they exit the vertebral column. This
collection of nerves in the vertebral canal is called the cauda equines (which means "horse
tail").