The back is a very complicated part of the human body. The "backbone" or spine, is a series of bony rings that run from the pelvis to the spine. The full weight of the body and head is held by the spine and the spinal-cord, the major route of nerves coming from the brain to the body and limbs, passes down inside the bony rings. Therefore the spine has both a mechanical role as well as a protective role.
The bony rings that make up the spine are called vertebrae. There are 7 vertebrae in the neck (7 cervical vertebrae), 12 in the chest area (12 thoracic vertebrae), 5 in the lower back (5 lumbar vertebrae) and then the sacrum. At the bottom of the sacrum, there is a small series of bones called the coccyx which are thought to be the remains of a tail in our ancestors.
The sacrum is held in place by the iliac bones - the two iliac bones and sacrum together being the bony pelvis or pelvic ring.
In between each of vertebrae is a disc, which acts as a shock absorber between the bones. Nerves go in and out of the spinal column between the vertebral bones, taking messages to and from the body and limbs. If one of these discs get damaged, and pushes on one of these nerves, it can cause intense pain such as sciatica. This is what we call a "slipped disc".
As the spine has to not only support the body and head, but allow it to move in all directions it needs to, it has a very large number of muscles surrounding it. Any of these muscles can get strained or will go into spasm if an injury occurs or a disc slips.
The complex relationship between the bones, muscles and discs mean that back pain and back problems are quite common in humans and to get to the bottom of these symptoms, certain doctors have become back specialists to become expert in this area.
Some back specialists come from a surgical background, being orthopaedic surgeons. Some come from a medical background, being a pain specialists. In addition, there non medical back specialists such as chiropractors and osteopaths.