The spine consists of 24 vertebrae (bones of the spine). These are split into three groups, seven cervical (neck), 12 thoracic (chest region) and 5 lumbar (lower back). The ribs attach each side to the thoracic vertebrae and stretch round to the front of the body joining to the sternum which is the plate of bone at the front of the chest.
The vertebrae are held in place by a complex collection of ligaments and muscles which should ensure each level can move independently of the next and become fixed when required to. The joints in between the vertebrae are known as facet joints and are generally flat. The orientation of the facet joints changes through the spine to allow different amounts of side bend and rotation movements in each level. The neck has a large amount of rotation while the lumbar spine has very little to reflect the needs of these areas.
The discs sit in between each vertebrae and are thus called intervertebral discs. These act as shock absorbers and aide motion. They consist of two parts. An outer shell (annulus fibrosus) and a jelly like centre called the nucleus pulposus. The outer shell is a semi rigid structure built in layers resembling and onion.
The vertebrae have a hole behind the main section and the section you can feel if you run your fingers down your spine. This accommodates the spinal cord which consists of the individual nerves as they travel to and from the brain. At each level one nerve bundle leaves from each side of the spinal cord, passing close to the facet joint before travelling to the head, arms, thorax or legs. The lower down the spinal cord, in general the lower down the body the nerves travel to. The cervical nerves go to the head and arms, the thoracic nerves to the thorax and the lumbar nerves top the legs.