Cavernosus muscle contraction during erection: is it voluntary or reflex, given the striated nature of the muscles?
The bulbo- and ischio-cavernosus muscles (BCM, ICM) contract in the rigid erection phase, leading to a suprasystolic cavernosal pressure. We investigated the hypothesis that the contraction of cavernosal muscles is reflexogenic despite their striated nature. The intracavernosal pressure (ICP) and the cavernosus muscles' electromyography (EMG) were recorded in 18 healthy volunteers in the flaccid and erectile phases. The test was repeated after separate anesthetization of the cavernosus muscles and the corpora cavernosa while the penis was in the rigid erection phase. The ICM and BCM showed no EMG activity with tumescence and full erection. When the ICP reached a mean of 148.6 +/- 9.4 cm H2O, both the ICM and BCM showed increased EMG activity. The suprasystolic pressure was intermittent and corresponded to the intermittent BCM and ICM contraction. Voluntary cavernosus muscle contraction did not increase the ICP at the different stages of erection. Anesthetization of the penis in the rigid erection phase led to disappearance of the cavernosus muscles' EMG activity, while bland gel application did not. Anesthetization of the 2 contracting cavernosus muscles, while the penis was in the rigid phase, produced an ICP drop to 69.5 +/- 7.6 cm H2O; repetition with saline did not affect the ICP. Cavernosus muscle contraction on corporal pressure elevation seems to be reflex and mediated through the corporo-cavernosal reflex (CCR). Changes in the evoked response amplitude would indicate a defect in the reflex pathway.