Innervation of the human anterior urethra by the dorsal nerve of the penis

Abstract

Previous neuroanatomic studies have demonstrated that branches of the dorsal nerve of the penis (DNP) innervate the anterior urethra. This study utilized electrodiagnostic techniques to confirm this finding. The portion of the male urinary tract distal to the prostate and genitourinary diaphragm is known as the anterior urethra. The innervation of the anterior urethra in the cat has been shown to be mediated through branches of the pudendal nerve. 1,9 The somatosensory innervation of the human penis is mediated primarily through the dorsal nerve of the penis (DNP). The DNP provides for afferent input from the skin of the penis and is crucially involved in male sexual reflex pathways for erection and ejaculation. 2,3,5 In neuroanatomic studies in the human, branches of the DNP were observed to penetrate the corpus spongiosum to innervate the urethra. This report is an electrodiagnostic study on the somatic innervation of the human anterior urethra by the DNP. These data clarify how urethral afferent information contributes to reflex sexual function, particularly ejaculation. METHODSTen healthy male volunteers aged 29-45 years (mean age 33) were enrolled in this study after protocol approval from the University of Washington Human Subjects Review Committee. None of the subjects had any physical evidence of penile neuropathy or history of genitourinary surgery, and all reported normal urinary and sexual function.Ten minutes prior to electrodiagnostic testing, a pharmacologic erection was induced by intracorporeal injection of alprostadil (prostaglandin E 1 ) 0.4 mL at the lateral base of the penis. This was done to increase the surface area of the penis and urethral length, which facilitated the electrode placement and positioning. Attempts to perform electrodiagnostic testing in subjects without an erection resulted in inconsistent results, primarily as a result of the inability to keep the catheter and electrodes in a fixed position within the urethra. Electrodiagnostic testing was commenced after the attainment of full tumescence and at approximately 50% rigidity of the subject's usual erectile capacity. Penile length was measured in the erect state from the base of the penis to the corona. We do not believe that the medication used to induce erection resulted in changes in axonal excitability. 12Two 10-mm (0.4 mm diameter) monopolar needle electrodes were placed subdermally at the base of the penis. Previous dissections showed the DNP to be a single trunk on both sides of the dorsal midline at the penile base. As the nerves traveled distally on the penile shaft, ventrolateral radiations of fibers emanated from the midline trunks (Yang and Bradley, submitted for publication). The electrodes were positioned so that they overlay the main trunks of both DNPs, perpendicular to the direction of the nerves. They were aligned along the dorsal midline of the penis with the anode positioned 1 cm

Bulbocavernosus Reflex to Stimulation of Prostatic Urethra in Patients with Lifelong Premature Ejaculation

“…The BC muscle is a paired, striated muscle surrounding the bulbous urethra, which has been reported to be closely related to ejaculation by its clonic contractions and other perineal muscles to expel the semen from the urethra [29–31]. Its contraction could be evoked by stimulation of penile skin, anterior urethra, and posterior urethra [26,32,33]. Innervation of penile skin and anterior urethra is penile dorsal nerve (somatic nerve).…”

Reflex innervation of the bulbocavernosus muscle

“…squeezing the glans or by electrostimulation) is an example of this alternate flexor response. The afferent impulses from the DNP originate from two separate sets of axons, one from the glans and the other from the anterior urethra [4] ( Fig. 4).…”

“…Afferent impulses stimulating reflex BCM contractions are carried through the dorsal nerve of the penis (DNP) to the sacral spinal cord, and efferent impulses are conveyed through the perineal nerve to the BCM. This can be shown clinically by squeezing the glans penis and palpating the BCM contraction [1,2], and electrophysiologically both from stimulation of the penile skin [3] and from the anterior urethra [4]. Electrophysiological techniques have been used routinely to determine the integrity of sacral innervation [5–7].…”

Cadaveric study of nerves supplying the membranous urethra

“…The dorsal nerve of the penis is thought to be a sensory nerve and its role in male sexual function has been extensively investigated by anatomical dissections and electrophysiological studies. 22,23 We suggest that the branches of the dorsal nerve of penis are responsible for urinary continence. Impaired seemed to be associated with membranous urethral sensitivity, particularly in patients with occasional urinary leakage.…”