The intervertebral disc is a structure that sits between two vertebral bones. It acts as a spacer and cushion while simultaneously facilitating and limiting motion.

The outer part of the disc is called the annulus fibrosus. It is a fibrocartilagenous structure comprised of type I and type II collagen.

The inner part of the disc is called the nucleus pulposus. It is made up of water, proteoglycans, and a loose network of collagen fibers.

The annulus fibrosus (outer part of the disc) holds in the nucleus pulposus (inner part of the disc). During motion the nucleus pulposus shifts and moves and pushes out against the annulus. This function allows forces to be distributed more evenly across the disc and the vertebral bones.