Nucleus Pulposus and How It Helps Your Spine

Most of us are not interested in the details of our spinal anatomy until we get injured. The nucleus pulposus is one such anatomical detail. It normally stays out of our awareness, living between two vertebrae, where it plays a major role in providing the spine with shock absorption during movement. It is one of the design features that prevents, or at least reduces the possibility of, an injury, or the pain that could otherwise come with bone on bone contact.

Illustration of the inside of the spine
PixologicStudio / Getty Images

What Is the Nucleus Pulposus?

Okay, maybe your interest is piqued. What is this nucleus pulposus?

The answer is, it's part of the intervertebral disc. The nucleus pulposus is the soft filling located in the center of the disc. It is contained by a strong covering consisting of 3 concentric layers of tough fibrous tissue. The covering is called the annulus fibrosus.

Nucleus Pulposus as Shock Absorber

The intervertebral disc is regarded by most experts as a shock-absorbing cushion that lives between adjacent spinal bones. But without the centralized nucleus pulposus, this shock absorption function is greatly diminished.

The intervertebral disc moves as you move. For example, when you arch your back, the disc migrates forward a bit; when you twist, the disc twists, too.

The strong outer fibers of the annulus fibrosus have the effect of packaging the nucleus pulposus and keeping it safely inside. But it's the nucleus that allows the disc to be so moveable, and to respond to your movement with movement of its own.

Spinal Action

Your spinal movements are supported by the water balloon-like shape and consistency of the disc, which in large part is due to the characteristics of the nucleus pulposus.

When you bend, twist, arch or tilt your spine, the nucleus is busy doing something similar to a swiveling action. which allows it to accommodate these actions.

Let's take the example of bending forward to pick something up from the floor. This action may involve a motion called forward spinal flexion, which is basically rounding over at the spine. When you bend forward this way, the spinal bones come closer together in front, which pushes the movable nucleus toward the back.

Many times per day, the repeated spinal actions of twisting, tilting, arching, rounding, etc. contribute to activities with which you are likely intimately acquainted. The shortlist includes shifting your position while you sit, working out and playing sports, unloading groceries and putting them in the fridge, and much more.

Disc Injury

With persistent or excessive spinal flexion, the disc may be pushed too far back. If the fibers of the annulus fibrosus are weak or torn, the nucleus may escape between them. When it does, it may come into contact with the nearby spinal nerve root, causing pain and other symptoms. This injury is called a herniated disc. Generally, the nucleus pulposus will escape in a combination side and back direction, which approximately corresponds to the location of the very sensitive nerve root with which it may come into contact.

The two most common causes of a disc herniation are degenerative changes in the disc, which you may know as wear and tear, and trauma to the disc. Disc degeneration occurs with age; it weakens the fibers of the annulus, allowing the nucleus to either distend or bulge, or to herniate.

Aging and the Nucleus Pulposus

As mentioned above, disc degeneration tends to come with age. It also accompanies, to a lesser extent, injuries to the area.

In young people, the nucleus pulposus is made mostly of water. So for this age group, a herniation due to trauma is more likely than in older people.

But as we get older, the disc, especially the nucleus pulposus dries out. This dehydration leads to a significant loss of disc height. By the time you're 60 or 70, your discs may be composed entirely of fiber. In this case, the shock absorption function of the disc is, for the most part, lost.

A Word From Verywell

The near-liquid consistency of the nucleus fibrosis makes it responsive indeed. But another function one of its functions is to buoy the spine; this helps prevent pressure on the bones.

A good rule of thumb when protecting your discs from injury on a day to day basis is to do your best to avoid forward spinal bending. Many times, you can replace that particular movement by bending at your hips, knees, and ankles.

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