Nocturnal penile tumescence


Nocturnal penile tumescence is a spontaneous erection of the penis during sleep or when waking up. Along with nocturnal clitoral tumescence, it is also known as sleep-related erection. Men without physiological erectile dysfunction or severe depression experience nocturnal penile tumescence, usually three to five times during a period of sleep, typically during rapid eye movement sleep. Nocturnal penile tumescence is believed to contribute to penile health.

Diagnostic value

The existence and predictability of nocturnal tumescence is used by sexual health practitioners to ascertain whether a given case of erectile dysfunction is psychological or physiological in origin. A patient presenting with erectile dysfunction is fitted with an elastic device to wear around his penis during sleep; the device detects changes in girth and relays the information to a computer for later analysis. If nocturnal tumescence is detected, then the erectile dysfunction is presumed to be due to a psychosomatic illness such as sexual anxiety; if not, then it is presumed to be due to a physiological cause.

Mechanism

The cause of nocturnal penile tumescence is not known with certainty. Bancroft hypothesizes that the noradrenergic neurons of the locus ceruleus are inhibitory to penile erection, and that the cessation of their discharge that occurs during rapid eye movement sleep may allow testosterone-related excitatory actions to manifest as nocturnal penile tumescence. Suh et al. recognizes that in particular the spinal regulation of the cervical cord is critical for nocturnal erectile activity.
Evidence supporting the possibility that a full bladder can stimulate an erection has existed for some time and is characterized as a 'reflex erection'. The nerves that control a man’s ability to have a reflex erection are located in the sacral nerves of the spinal cord. A full bladder is known to mildly stimulate nerves in the same region.
The possibility of a full bladder causing an erection, especially during sleep, is perhaps further supported by the beneficial physiological effect of an erection inhibiting urination, thereby helping to avoid nocturnal enuresis. However, given females have a similar phenomenon called nocturnal clitoral tumescence, prevention of nocturnal enuresis is not likely a sole supporting cause.

In popular culture

Research into the causes of nocturnal penile tumescence was the subject of "The Mystery of Morning Wood", a 1995 episode of the animated comedy series Beavis and Butt-head.