Fig. 3. Nociceptor conduction velocities. Example of digitized oscilloscope trace of action potentials evoked by electrical stimulation at the receptive field of an Aδ- (A ) and C-nociceptor (B ). Open arrow head, electrical stimulation; filled arrow, evoked action potential. The distribution of conduction velocities of each Aδ- (C ) and C-nociceptor (D ) in each of the four groups. Open circle, nociceptors without spontaneous activity; filled circle, nociceptors with spontaneous activity. POD = postoperative day.