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Anatomy of the Spine

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Spine Anatomy DiagramThe spine is made up of bones called vertebrae or vertebral bodies. There are 7 cervical vertebrae within the neck, 12 thoracic vertebrae are attached to he ribs on each 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 joins the pelvis through the sacro-iliac joints. Below the sacrum is the coccyx.

Looking at the spine from the back it appears to be straight. From the side there are several curves, in the cervical spine the neck curves backwards (lordosis), in the thoracic spine it curves forwards (kyphosis). Again in the lumbar spine it curves backwards (lordosis).

Spine Vertebrae

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

Each vertebra consists of the vertebral body at the front, the pedicles at the sides and the lamina at the back of the spine. This creates a bony canal in the centre for the spinal cord. At the back of the vertebrae there are a pair of facet joints which articulate with the facet joints of the adjacent vertebra.

At each level of the spinal column a pair nerve root exits through a hole (neural foramen). 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 specific muscles (myotome).

Facet Joints in MotionBetween 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 which area of the spine, with greater movement possible in the cervical and lumbar regions.

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

 

Cervical Facet JointsThe upper two cervical vertebrae have a different structure compared with the other vertebral bodies.