Discs have a jellylike center(nucleus) and a tough outer ring(annulus). Normally, the nucleus is filled with fluid. Movement pushes fluid in and out of the nucleus. This keeps the disc healthy. Disc size, shape, and flexibility change throughout the day.
Three Curves of the Spine
The spine has three curves: the cervical curve(neck), thoracic curve(midback), and lumbar curve(lowback). When properly aligned, these curves help your body in balance. They also help distribute your weight along your spine.