A normal disc is compared to a jelly-filled donut. The outside is called the annulus and inner jelly is the nucleus. The nucleus absorbs shock.

As you can see from the picture above, the top image is a normal disc with normal height and alignment. As the disease progress, the discs lose height, calcification occurs and significant spinal nerve compression as shown in the images above.

Excessive movements or forces through the spine cause microscopic tears in the annulus.

A disc bulge occurs as the nucleus moves through the annular tears creating an outward protrusion. A Herniated disc occurs when the nucleus pushes through the annulus.

Both conditions can irritate or compress surrounding structures.