Reflex innervation of the bulbocavernosus muscle

Objective To determine the somatic reflex innervation of the bulbocavernosu s muscle (BCM) and to illustrate the role of the perineal nerve in BCM cont raction, using electrophysiological techniques. Subjects and methods Ten healthy, potent men underwent genital electrophysi ological testing. Stimuli were applied to the dorsal nerve of the penis at the base of the penis, glans and anterior urethra, and the perineal nerve b ranch to the BCM. The electromyographic (EMG) responses of the BCM were rec orded and onset latencies measured at baseline, both after anaesthetising t he perineal nerve and after recovery from the anaesthetic. Results A reflex BCM contraction was elicited from all stimulation sites. A naesthetizing the perineal nerve resulted in alterations of the EMG respons e. After the anaesthetic effect wore off, the responses returned to baselin e values. Conclusions Three distinct somatic bulbocavernosus reflexes were detected w hich are components of normal ejaculation. BCM contraction can be elicited after stimulating the dorsal penile nerve at the glans and the anterior ure thra; these are the flexor responses of the bulbocavernosus reflex. BCM con traction can also be induced on stimulating the perineal nerve, which is th e pathway through which the stretch and the tendon organ reflexes are carri ed to mediate muscle tone. The motor innervation of the BCM for all reflexe s is carried through a branch of the perineal nerve. The findings may be re levant to the evaluation of ejaculatory disorders.