Pain perception involves nociceptor activation, signal transmission via A-delta and C fibers, dorsal horn processing in the spinal cord, and cortical interpretation in the somatosensory cortex. Central sensitization occurs when repeated nociceptive input causes N-methyl-D-aspartate (NMDA) receptor activation in dorsal horn neurons, leading to enhanced neuronal excitability, expanded receptive fields, and amplified pain signaling — this mechanism underlies chronic pain conditions such as fibromyalgia, complex regional pain syndrome, and chronic post-surgical pain. The wind-up phenomenon describes progressive increases in dorsal horn neuron firing with repeated C-fiber stimulation at the same intensity, representing temporal summation of pain. Gate control theory explains how non-nociceptive input (touch, pressure) can modulate pain transmission through inhibitory interneurons in the substantia gelatinosa.