Answer by  
                                                                                          InduNambiar (8)
                                                            
                          
                          
                                                          There are annular fibers which are concentric ring like things surrounding the nucleus of the discs in the spine. When there is a tear in the ring, herniation of the nucleus pulposes through the rings causes focal protrusion, the disk bulges outward beyond the the vertical margin, causing disc herniation.