Reflex innervation of the bulbocavernosus muscle

To determine the somatic reflex innervation of the bulbocavernosus muscle (BCM) and to illustrate the role of the perineal nerve in BCM contraction, using electrophysiological techniques. Subjects and methods Ten healthy, potent men underwent genital electrophysiological 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 branch to the BCM. The electromyographic (EMG) responses of the BCM were recorded and onset latencies measured at baseline, both after anaesthetising the perineal nerve and after recovery from the anaesthetic.

A reflex BCM contraction was elicited from all stimulation sites. Anaesthetizing the perineal nerve resulted in alterations of the EMG response. After the anaesthetic effect wore off, the responses returned to baseline values.

Three distinct somatic bulbocavernosus reflexes were detected which are components of normal ejaculation. BCM contraction can be elicited after stimulating the dorsal penile nerve at the glans and the anterior urethra; these are the flexor responses of the bulbocavernosus reflex. BCM contraction can also be induced on stimulating the perineal nerve, which is the pathway through which the stretch and the tendon organ reflexes are carried to mediate muscle tone. The motor innervation of the BCM for all reflexes is carried through a branch of the perineal nerve. The findings may be relevant to the evaluation of ejaculatory disorders.