Study on the origin of the external anal, urethral, vaginal and prostatic sphincters.

The response of the external anal, urethral, prostatic and vaginal sphincters to stimulation of the puborectalis muscle was studied aiming at the physiological validation of their origin from the PRM. Twenty-eight healthy volunteers were examined (16 men, 12 women: mean age 40.6 +/- 8.3 SD years). The PRM was stimulated by a needle electrode and the response of the EAS and EUS recorded. The PS and VS were monitored by manometric measuring of the urethral and vaginal pressures. Upon stimulation, the EMG activity of the EAS (P < 0.001) and EUS (P < 0.001), as well as of the prostatic urethral (P < 0.05) and vaginal (P < 0.0001) pressures, increased. There was no response to stimulation of the anesthetized PRM; this might indicate that the sphincters contract in response to PRM stimulation. The EMG recorded no latency, suggesting that the motor units of the EAS and EUS were simultaneously activated with those of the PRM, and also that their muscle fibers seem to be directly derived from the PRM. However, proof of PS and VS continuity with PRM could not be supplied by the study.