What is defined as a "herniated disc"?

A herniated disc is defined as a condition where the disc protrudes and compresses nearby nerves. This occurs when the inner gel-like center of the disc (nucleus pulposus) pushes through a tear in the outer layer (annulus fibrosus). Such protrusion can lead to pain, numbness, or weakness in the areas where the affected nerves travel, often resulting in symptoms that radiate into the arms or legs depending on the location of the herniation in the spine.

This condition is specifically related to the disc's structure and its interaction with spinal nerves, making option B the most accurate definition. Other options describe different spinal conditions, not related to the specific mechanical dysfunction associated with a herniated disc. For example, reducing spinal mobility refers to stiffness or limitations in movement but doesn't capture the essence of nerve compression; excessive curvature pertains to scoliosis or lordosis, and muscle spasm indicates muscular issues rather than disc herniation.