Final answer:
A herniated disc happens when the nucleus pulposus protrudes through a weakened or torn annulus fibrosus, often leading to nerve compression and associated pain or muscle weakness.
Step-by-step explanation:
A herniated disc occurs when the nucleus pulposus breaks through the annulus fibrosus. This condition involves the gel-like center of the intervertebral disc, the nucleus pulposus, protruding through a tear or weakness in the fibrous outer layer, the annulus fibrosus. Such an event can lead to the compression of a spinal nerve, resulting in pain and possible muscle weakness in the regions of the body that the affected nerve supplies.
A herniated disc is commonly referred to as a 'ruptured' or 'slipped' disc and can result from factors such as injury, aging, or lifting heavy objects. This condition is most prevalent in the L4/L5 or L5/S1 intervertebral discs, potentially causing sciatica. Conversely, if the herniation occurs in the cervical region, such as at C5/C6 or C6/C7, it can lead to pain in the neck, shoulder, and upper limb.