The nucleus pulposus is the soft center of the intervertebral disc. It is contained by a strong covering known as the annulus fibrosus.
In young people, the nucleus pulposus is made mostly of water. As we get older, it dries out. This dehydration results in a significant loss of disc height. By the age of 60 to 70, the disc is composed entirely of fiber.
The nucleus pulposus is responsible for shock absorption. You might think of it as a pillow or cushion that moves as you move. For example, when you bend forward, the spinal bones come closer together in front, which pushes the nucleus toward the back. The nucleus pulposus helps prevent pressure on the spine as you sit, stand, walk or engage in activities.