Gating mechanism of pain is proposed by Melzack and Wall, this theory explains why we experience different pain intensities in different situations. If we met with any injury, the impulses of nociception (pain) are transmitted up to the brain via the spinal cord.
During this pathway, the pain passes through the nerve gates that allow them to pass to brain. If these nerve gates block the gates, the pain impulses do not reach brain or few impulses reach the brain, so the intensity is less. If these impulses reach brain more readily, the intensity of pain is more.
Thus, the blank can be filled with “pain gate.”