The spinal cord itself is one of the bodies' most important systems, vital to the transfer of neural signals between the brain and the rest of the body. What many people forget is that the spinal system itself consists not just of lumbar vertebrae, but also major components of the central nervous system. It is divided into 31 different parts, segmented into three main sections - "upper back", "mid back" and "lower back". This is important to note because each one of these 31 parts controls various sensations in the body through spinal nerves. In addition to the nerves, there are major arteries running through the back as well, including the left and right posterior arteries.