Pulsatile emission of semen from the penis is generated by the reflex contraction of the bulbospongiosus muscle that forces semen from the base of the penis and out of the external urethral meatus. Bulbospongiosus muscle is innervated by somatic motor fibers carried in the pudendal nerve (S2–S4). Contraction of the internal urethral sphincter and periurethral smooth muscle, innervated by the sympathetic part of the visceral nervous system, prevents retrograde ejaculation into the bladder.
In the clinic
Erectile dysfunction (ED) is a complex condition in which men are unable to initiate or maintain penile erection. When this affects erections during sleep, and with self-stimulation as well as with a partner, vascular and/or nerve impairment is present. This generalized type of ED increases with age and is recognized as a risk factor for coronary artery disease. It is frequently associated with cardiovascular disease, diabetes, and neurological conditions including Parkinson’s disease, spinal cord injuries, multiple sclerosis, and as nerve damage from pelvic surgeries or radiation for pelvic malignancies. Low testosterone states can impair erections and consistently prevent sleep-induced erections. Medications including serotonin reuptake inhibitors (SSRIs), thiazides and anti-androgens can also underlie ED. When only partnered erections are problematic, psychological factors underlie the dysfunction—the normal erections from sleep confirming healthy vascular and neurological function. Most cases of ED are multifactorial in etiology, and all markedly lessen quality of life and a person’s well-being and can lead to depression and low self-esteem as well as emotional and social isolation.
Delayed (or absent) ejaculation can result from nerve damage in conditions such as diabetes, Parkinson’s disease, spinal cord injuries, multiple sclerosis, complications after major pelvic surgeries and pelvic irradiation. Ejaculation is absent after radical prostatectomy for prostate cancer (which also removes the seminal vesicles), but orgasm is still possible as the pudendal nerve is spared. SSRIs, neuroleptics, alcohol, and recreational drugs (marijuana, cocaine, and heroin) often delay orgasm and therefore ejaculation, as in health the two coincide (even though the nerves involved are different).
Because erectile tissues in the clitoris have similar innervation and blood supply to the penis, vulvar swelling is likely compromised by the same conditions that cause ED in men. However, it appears that this is a rare cause of female sexual dysfunction. Reduced clitoral swelling is rarely symptomatic. Note that phosphodiesterase type 5 (PDE5) inhibitors (sildenafil) do not improve female sexual dysfunction even in conditions such as diabetes. Research confirms that otherwise healthy women with complaints of low sexual arousal have a physiologically normal increase in genital congestion in response to visual sexual stimuli, even though they do not find the stimuli mentally sexually arousing. Loss of genital sexual sensitivity from somatic nerve damage from multiple sclerosis or diabetes can be highly symptomatic and preclude orgasm. Medications preventing orgasm in men can also affect women.
In the clinic
Urethral rupture may occur at a series of well-defined anatomical points.
The commonest injury is a rupture of the proximal spongy urethra below the perineal membrane. The urethra is usually torn when structures of the perineum are caught between a hard object (e.g., a steel beam or crossbar of a bicycle) and the inferior pubic arch. Urine escapes through the rupture into the superficial perineal pouch and descends into the scrotum and up onto the anterior abdominal wall deep to the superficial fascia.
In association with severe pelvic fractures, urethral rupture may occur at the prostatomembranous junction above the deep perineal pouch. The urine will extravasate into the true pelvis.