Schematic diagram of physiological model of vulvar pain

A illustrates the immediate response to cutaneous trauma. Action potentials in C-nociceptors propagate through the dorsal root ganglion (DRG) to the spinal cord where they activate and sensitize wide-dynamic-range (WDR) neurons whose axons ascend to higher centers. In B, the WDR neurons remain sensitized and now respond to activity in large diameter A-mechanoreceptors which are activated by light touch. This state produces allodynia. In C, the same sensitized WDR neurons respond again to A-mechanoreceptors activity, but this activity is initiated by sympathetic efferent actions on the sensory receptor, in the absence of cutaneous stimulation. This phase represents sympathetically maintained pain. Although spinal interneurons are shown to be interposed in the 'pain' pathway, this is just one of the many possible arrangements.