Disc herniation involves the nucleus pulposus migrating through which part of the disc?

• A. Annulus fibrosus through nucleus pulposus
• B. Spinal cord through the vertebral foramen
• C. Nucleus pulposus through the vertebral body
• D. Nucleus pulposus through annulus fibrosus

Answer: (D)

Disc herniation occurs when the nucleus pulposus, the soft gel-like center of the disc, is forced through a tear or weakness in the outer ring called the annulus fibrosus. The annulus fibrosus normally contains the nucleus, but if it becomes weakened or damaged, the nucleus can protrude outward into the spinal canal, potentially pressing on nerve roots. This pathway—nucleus pulposus moving through the annulus fibrosus—best explains the process. The other options describe structures or movements that aren’t involved in a disc herniation (such as the nucleus moving through the vertebral body or the spinal cord moving through the vertebral foramen).