Structure and function of Spine
The spine has an interesting structure and links the skull at the top to the pelvis at bottom. It consists of chain of bones called ?vertebrae?, separated by tyre like shock absorbers called intervertebral discs. There are 33 vertebrae ? 7 in neck called cervical vertebrae, 12 in chest region called thoracic vertebrae, 5 in low back called lumbar vertebrae, 5 sacral vertebrae and 4 coccygeal vertebrae at tail end. Looking from side the vertebral column is ?S?shaped with forward curvature in cervical and lumbar region and backward curvature in the thoracic region. The forward curvature is referred to as lordosis and backward curvature as kyphosis.
Vertebra
The vertebra is composed of two parts. The front or anterior part is called the vertebral body and the back or posterior part is called as vertebral arch. These two parts form a ring through which passes the spinal cord, which carries nerves supplying different parts of the body. The vertebral arch is formed of pedicles and laminae, which form the posterior part of the ring. The various processes projecting from the junction of pedicle and lamina are transverse process, the superior articular facet and inferior articular facet. The junction of pedicle, lamina and the above structures is a hard ridge of bone called pars interarticularis. The two laminae join together to complete the ring. A bony structure, which projects backwards from the union of the laminae is called spinous process, which we can feel from our back
Intervertebral Discs
The intervertebral discs have two parts: the inner jelly like soft part is called nucleus pulposus and the outer fibrous hard part is called annulus fibrosus. The disc is hygroscopic, which means it has, water absorbing capacity. On loading it loses water and at night in resting position it absorbs water. Hence the height of an individual in morning is half an inch more than at evening. The disc starts degenerating due to stress and loses its water content. The outer annular fibres may tear resulting in pain. Sometimes the inner soft nuclear material may prolapse through the rent in fibres and compress a nerve root, which travels into leg. This condition is called as prolapse intervertebral disc or slip disc or sciatica.