The spine is made up of bones called vertebrae or vertebral bodies. There are 7 cervical vertebrae within the neck, 12 thoracic vertebrae which are attached to the ribs on either side to form the rib cage, and there are 5 lumbar vertebrae in the lower back. Below the lumbar spine lies the sacrum, which on either side connects to  the pelvis at the sacro-iliac joints. Below the sacrum is the coccyx.

Looking at the spine from the behind it appears to be straight. From the side the spine has  three curves, in the cervical spine the neck curves backwards (lordosis), in the thoracic spine it curves forwards (kyphosis), and again in the lumbar spine it curves backwards (lordosis). The three curves are such that the head lies directly above the pelvis.

At each level of the spine, except for the two cervical vertebrae at the top, the fundamental anatomy of the vertebrae are the same, although the size and shape varies between the different areas of the spine.

Each vertebra consists of the vertebral body at the front, a pedicle on either side and the lamina at the back.  These bony structures form a  bony ring, called the spinal canal, the spinal cord lies within this canal, protected by the bone. At the back of each  vertebra there are two pairs of facet joints which articulate with the facet joints of the adjacent vertebrae, above and below. .

At each level of the spinal column a pair nerve root exits through a hole (neural foramen), on each side. Within the cervical and lumbar spine these nerve roots join together to form the cervical and lumbar plexuses, which supply the arms and legs respectively.

Each individual nerve root supplies a specific area of the skin (dermatome) and a group of muscles (myotome), each myotome moves a joint in a certain direction.

Between each vertebra there are three joints – the disc between the bodies at the front, and two smaller facet joints at the back of the spine. This constitutes a “motion segment” of the spine. The amount of movement within a given motion segment varies depending on the area of the spine, with greatest  movement possible in the cervical spine, and the least within the thoracic spine.

The vertebral bodies are separated by cushions called intervertebral discs. A disc is made of special cartilage and acts like a shock absorber between the vertebral bodies. The disc is made of two parts – the outer layers form the annulus fibrosis, fibres arranged in a circular pattern. In the centre of the disc is the nucleus pulposis, which has a more gelatinous material. When the annulus tears central nucleus may prolapse through the annulus and press on the nerve root.

Each of the upper two cervical vertebrae, C1 and C2,  have unique anatomy, different from each other and all the  other vertebral bodies.