Structure of the Spine

The spinal column consists of 33 vertebrae (bones) stacked on top of each other; the upper 5 form the cervical spine (neck), the next 12 form the thoracic spine (mid-back), and next five form the lumbar spine (lower back). The remaining 9 vertebrae form the sacrum and coccyx and are fused together and immobile. When looking at the spine from the side, the vertebrae form an S shape. This creates an even distribution of weight along the spine, and allows the spine to withstand all kinds of stress.

Vertebrae and Discs

Shock-absorbing discs sit between the bodies of the vertebrae, helping to absorb pressure and keep the bones from rubbing against each other. Discs consist of a semi-fluid core and a tough elastic outer layer. They act hydraulically; every time a vertebral body shifts with respect to its neighbour the semi-fluid core of the disc shifts accordingly, and the disk bulges out to one side.

The vertebrae are linked together by facet joints. These allow the surfaces of the joints to glide against one another, enabling movement in all directions. The angle of the joints determines the movement that each vertebra can make. Strong ligaments bind the vertebrae together and keep the spine stable.

Movement in the Spine

Together, the joints and discs between the vertebrae allow for a great deal of movement, while still ensuring spinal stability. Backward bending pushes the vertebral arches together, compressing the posterior part and spreading the anterior part of the disc, pushing the vertebral bodies apart. Forward bending pulls the vertebral arches apart and compresses the discs in front. In spinal twists the disc is symmetrically compressed and bulges out evenly on all sides.