The mechanism of ejaculation: the glans-vasal and urethromuscular reflexes.

To assist in the understanding of the pathogenesis of the various ejaculatory disorders, 9 healthy male volunteers (mean age 30.4 +/- 4.8 years) were studied. The EMG response of the bulbocavernosus (BCM) and ischiocavernosus (ICM) muscles and the external urethral sphincter (EUS) to ejaculation induced by glans penis (GP) vibration was recorded. The test was repeated with individual anesthetization of the GP, BCM, ICM, and EUS. During ejaculation, the BCM, ICM, and EUS showed a significant increase in the motor unit action potentials. The contractions were rhythmic with a mean duration of the contractile episode of 0.8 s and the noncontractile episode of 0.72 s, and with a total muscle activity of 4.2 s. GP vibration after anesthetization of the GP produced no ejaculation or increased EMG activity of the BCM, ICM, and EUS, GP vibration after individual anesthetization of the BCM or the EUS produced semen emission but no ejection, and GP vibration after ICM anesthetization produced ejaculation (emission and ejection). The results suggest that the ejaculatory mechanism consists of two reflexes: the glans-vasal and urethromuscular. The former seems to bring the semen to the posterior urethra (the emission stage of ejaculation) and the urethromuscular reflex ejects it to the exterior (ejection stage of ejaculation). A dysfunction of these two reflexes would seem to induce ejaculatory disorders, a point that needs further study.