Your back (spine) supports the body and allows us to do activities such as walking, running, lifting, and twisting. It is made up of bone segments called vertebrae. Between the bones of the spine are small discs that are hard on the outside, and soft and jelly-like on the inside. The spinal bones are connected by the facet joints at the back and by the discs at the front.
The nerves of the spinal cord carry messages between the brain and body. They run along the spine through the spinal canal. They separate into roots along the length of the spinal cord and at the tail end of the spine. Some of them pass through the pelvis to become the sciatic nerves, which pass down each leg.