Nocturnal penile tumescence is a spontaneous

erection An erection (clinically: penile erection or penile tumescence) is a physiological phenomenon in which the penis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, vascular, ...

of the

penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males do n ...

during

sleep Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...

or when waking up. Along with

nocturnal clitoral tumescence Nocturnal clitoral tumescence (NCT), colloquially known as morning bean, is a spontaneous swelling of the clitoris during sleep or when waking up. Similar to the process in males, nocturnal penile tumescence, females experience clitoris tumescen ...

, it is also known as sleep-related erection, morning glory or morning wood. Men without physiological

erectile dysfunction Erectile dysfunction (ED), also called impotence, is the type of sexual dysfunction in which the penis fails to become or stay erect during sexual activity. It is the most common sexual problem in men.Cunningham GR, Rosen RC. Overview of male ...

or severe depression experience nocturnal penile tumescence, usually three to five times during a period of sleep, typically during

rapid eye movement sleep Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream viv ...

. Nocturnal penile tumescence is believed to contribute to penile health.

Mechanism

The cause of nocturnal penile tumescence is not known with certainty. In a wakeful state, in the presence of mechanical stimulation with or without an arousal, erection is initiated by the parasympathetic division of the autonomic nervous system with minimal input from the central nervous system. Parasympathetic branches extend from the sacral plexus of the spinal nerves into the arteries supplying the erectile tissue; upon stimulation, these nerve branches release acetylcholine, which in turn causes release of nitric oxide from endothelial cells in the trabecular arteries, that eventually causes tumescence. Bancroft (2005) hypothesizes that the

noradrenergic Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad'', ...

neurons of the

locus ceruleus The locus coeruleus () (LC), also spelled locus caeruleus or locus ceruleus, is a nucleus in the pons of the brainstem involved with physiological responses to stress and panic. It is a part of the reticular activating system. The locus coeru ...

in the brain are perpetually inhibitory to penile erection, and that the cessation of their discharge that occurs during rapid eye movement sleep may allow

testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...

-related excitatory actions to manifest as nocturnal penile tumescence. Suh et al. (2003) recognizes that in particular the spinal regulation of the cervical cord is critical for nocturnal erectile activity. The nerves that control one's ability to have a reflex erection are located in the

sacral nerves A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...

(S2-S4) of the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

. Evidence supporting the possibility that a full

bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...

can stimulate an erection has existed for some time and is characterized as a 'reflex erection'. 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 Nocturnal enuresis, also informally called bedwetting, is urinary incontinence, involuntary urination while sleep, asleep after the age at which bladder control usually begins. Bedwetting in children and adults can result in emotional stress. Com ...

. However, given females have a similar phenomenon called

, prevention of nocturnal enuresis (bed-wetting) is not likely a sole supporting cause. In a study published in 1972, during puberty, the average tumescence time per night was 159 min; average REM sleep time was 137 min. Average simultaneous REM sleep and penile tumescence per night was 102 min. Study subjects averaged 6.85 tumescence episodes/night, and, of these, 5.15 occurred during a REM sleep period. Tumescence episodes during REM averaged 30.8 min in duration, whereas episodes which occurred when no REM was present averaged 11.75 min. Study subjects had at least four REM periods per night and at least three tumescence episodes. In another study of healthy older people published in 1988, frequency and duration of nocturnal penile tumescence decreased progressively with age independent of variations in sleep. In contrast to younger age groups, the majority of those above age 60 did not have full sleep erections even though they and their partners reported regular intercourse. Unlike physiological penile tumescence, sleep-related painful erections (SRPE) and stuttering

priapism Priapism is a condition in which a penis remains erect for hours in the absence of stimulation or after stimulation has ended. There are three types: ischemic (low-flow), nonischemic (high-flow), and recurrent ischemic (intermittent). Most cases ...

(SP) are much rarer pathological erections, resulting in poor sleep and daytime tiredness, and long term cardiovascular morbidity. SRPE is a rare parasomnia consisting of nocturnal penile tumescence accompanied by pain that awakens the individual. It occurs predominantly during REM sleep, without an apparent underlying illness or penile anatomic abnormalities . On the contrary, stuttering priapism can occur spontaneously at any time of the day, but more commonly so during REM sleep. SP is a subtype of ischemic priapism that is characterized by recurrent, self-limiting, painful erections that often require maneuvers (compression, cold packs or a cold shower, voiding, or exercise, etc.) to aid detumescence. In ischemic priapism, most of the penis is hard; however, the

glans penis In male human anatomy, the glans penis, commonly referred to as the glans, is the bulbous structure at the distal end of the human penis that is the human male's most sensitive erogenous zone and their primary anatomical source of sexual p ...

is not. Much rarer priapism is secondary to blunt trauma to the perineum or penis, with laceration of the cavernous artery, which can generate an arterial-lacunar fistula resulting in a high blood flow state, hence the tumescence. Tumescence lasting for more than four hours is a medical emergency. At the time being, no treatment consensus for SRPE has been established.

Baclofen Baclofen, sold under the brand name Lioresal among others, is a medication used to treat muscle spasticity such as from a spinal cord injury or multiple sclerosis. It may also be used for hiccups and muscle spasms near the end of life. It is ta ...

tablets taken before sleep is the most commonly used medication, having a tolerable profile of adverse effects.

Diagnostic value

The existence and predictability of nocturnal

tumescence Tumescence is the quality or state of being tumescent or swollen. Tumescence usually refers to the normal engorgement with blood (vascular congestion) of the erectile tissues, marking sexual excitation, and possible readiness for sexual activity. T ...

is used by

sexual health Sexual and reproductive health (SRH) is a field of research, healthcare, and social activism that explores the health of an individual's reproductive system and sexual wellbeing during all stages of their life. The term can also be further de ...

practitioners to ascertain whether a given case of erectile dysfunction is

psychological Psychology is the scientific study of mind and behavior. Psychology includes the study of conscious and unconscious phenomena, including feelings and thoughts. It is an academic discipline of immense scope, crossing the boundaries between t ...

physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

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 A somatic symptom disorder, formerly known as a somatoform disorder,(2013) dsm5.org. Retrieved April 8, 2014. is any mental disorder that manifests as physical symptoms that suggest illness or injury, but cannot be explained fully by a general ...

such as sexual anxiety; if not, then it is presumed to be due to a physiological cause.

Nocturnal penile tumescence testing

Regularly, those who experience

are given a nocturnal penile tumescence (NPT) test, usually over a three-day period. Such a test detects the presence of an erection occurring during sleep using either: # a small portable computer connected to two bands placed around the shaft of the penis which records penile tumescence, # a band of paper tape with perforations (similar to coil postage stamps) that is fit snugly around the shaft of the penis and will break at the perforations during penile tumescence. The goal of nocturnal penile tumescence testing is to determine whether one can experience an erection while sleeping after reporting that they are unable to experience an erection while awake. On average, one has 3–5 episodes of NPT each night, and each episode lasts 30–60 minutes, although the duration is reduced with advanced age. If one does obtain an erection while sleeping, but cannot obtain one while awake, a psychological cause or a medication side effect is usually suspected. Otherwise, if one does not obtain an erection in either state, a

cause is usually suspected.

Mechanism

Diagnostic value

Nocturnal penile tumescence testing

See also

Notes

References

Further reading