The anatomy of the spine is studied under three segments. These segments include 7 cervical, 12 dorsal, 5 lumbar vertebrae. Under lumbar vertebrae, there is respectively the sacrum and the coccyx (tailbone), which is a remainder of the evolutionary process. There are different parts in a spinal bone. The vertebral body is the most important part that carries weight.
Vertebral bodies are aligned on top of one another with the help of some flexible tissues called the intervertebral discs. Behind vertebral bodies, there are laminae that surrounds the spinal cord. Next to the laminae, there are two transverse processes and a spinous process that serve the attachment of muscles and ligaments. There are superior and inferior articular facet joints on each vertebra which serve the stability of the spine.
There are nerve roots between the vertebral bodies and the laminae. Some of the nerve roots that exit from the four lumbar vertebrae constitute the sciatic nerve. Sciatic nerve is located behind the pelvis and the hip, and it goes down through the thigh. Therefore, some diseases in the lumbar vertebrae (like spinal disc herniation and some tumors) involve a pain from the hip to the thigh.
Vertebral bodies are separated from one another by structures called the discs, the annulus and the soft gel-like material nucleus pulposus. Spinal disc herniation is the result of a tear in the outer ring (anulus fibrosus) of the intervertebral disc which lets some of this nucleus pulposus bulge out in a hernia and pressures the nerves in the spinal cord.