Fig (1) Self-regulation of the disk. Even in the steady state, the nucleus tends to expand but is restrained by the end-plates and the annulus. During axial compression, nucleus’ hydrostatic pressure rises, which counteracts the deformation. During flexion (in extension and lateral bending respectively) annulus fibers are stretched and the nucleus is pushed to the opposite side. The nucleus forces the fibers to return to their original state, thus countering the motion.