HUMAN ANATOMY

The spine is composed of 24 vertebral bodies that together support approximately half the body weight (the other half is supported by muscles). The vertebrae provide stability and protection to the spinal cord. The different parts of a vertebra can be seen in the picture below.

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The vertebral bodies are broken up into three major curves of the spine. These include the cervical spine (neck, 7 vertebral bodies), thoracic spine (upper back, 12 vertebral bodies), and lumbar spine (lower back, 5 vertebral bodies). Beneath the lumbar region lies the sacrum (between the L5 and the coccyx) and the tailbone, or coccyx. The curves of the spine allow it to support more weight than if it were straight (about 10 times!). The presence of the curves increases the resistance to axial compression (head-to-toe compression of the spine). 1,4,5,7,8

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Intervertebral discs are located between adjacent vertebral bodies to act as cushions. Discs are fibrocartilaginous structures that possess enormous strength. There are two main parts of a disc: the annulus fibrosus (outer concentric layers of fibrous tissue) and the nucleus pulposus (central springy, pulpy zone). 25% of the length of the vertebral column is due to the intervertebral discs. They increase in thickness as you move down the spinal column. At birth, approximately 80% of the disc is composed of water. Part of the aging process includes a reduction in the water content of the nucleus pulposus. The mucoid matrix is eventually replaced by fibrocartilage and it becomes increasingly similar to the annulus fibrosus. The disc does not have a blood supply, and therefore, no way to repair itself. Thus, damage to disc can be permanent. 1,2,3,6

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Flexion is achieved by the hips (50%) and by the lumbar spine (50%). The half that the lumbar spine is responsible for is divided between the five motion segments, with a disproportionate amount of the motion at L4-L5 (lumbar segment 4 and 5) and L3-L4 (lumbar segment 3 and 4). Hence, degeneration occurs most frequently at these two segments. The breakdown at these segments causes instability. 1,3

More information about the anatomy of the spine, symptoms associated with degenerative diseases, means of diagnosis, and treatment methods can be found at the cited references below.

1. Spine Health: http://www.spine-health.com/topics/anat/a02.html

2. Netter, F. 1991. The Ciba Collection of Medical Illustrations, Volume 8, Part 1. p 9-15. Ciba-Geigy Corporation. Summit.

3. Southern California Orthopedic Institute: http://www.scoi.com/spinanat.htm

4., 5., 9. http://www.medicalmultimediagroup.com/pated/back/back.html#anatomy

6. Rothman Institute webpage: http://rothmaninstitute.com/spine/anatomy.htm

7. Spinal Health: http://www.spinalhealth.net/ana.html

8. Back: http://www.back.com/anatomy

10. http://www.scoi.com/spinanat.htm

11. Spine Universe: http://www.spineuniverse.com/displayarticle1267erse.com/displayarticle.php/html