Nocturnal penile tumescence (NPT) is a spontaneous
erection
An erection (clinically: penile erection or penile tumescence) is a Physiology, physiological phenomenon in which the penis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, ...
of the
penis
A penis (; : penises or penes) is a sex organ through which male and hermaphrodite animals expel semen during copulation (zoology), copulation, and through which male placental mammals and marsupials also Urination, urinate.
The term ''pen ...
during
sleep
Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain Sensory nervous system, sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and interactions with th ...
or when waking up. Along with
nocturnal clitoral tumescence, it is also known as sleep-related erection. Colloquially, the term morning wood, or less commonly, morning glory is also used, although this is more commonly used to refer specifically to an erection ''beginning'' during sleep and persisting into the period just after waking. Men without physiological
erectile dysfunction
Erectile dysfunction (ED), also referred to as impotence, is a form of sexual dysfunction in males characterized by the persistent or recurring inability to achieve or maintain a Human penis, penile erection with sufficient rigidity and durat ...
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.
Mechanism
The cause of nocturnal penile tumescence is not known with certainty. In a wakeful state, in the presence of mechanical
stimulation
Stimulation is the encouragement of development or the cause of activity in general. For example, "The press provides stimulation of political discourse." An interesting or fun activity can be described as "stimulating", regardless of its physic ...
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 neurons of the
locus ceruleus 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 male sex hormone and androgen in Male, males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testicles and prostate, as well as promoting se ...
-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 (S2-S4) of the
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...
. Evidence supporting the possibility that a full
bladder 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 (NE), also informally called bedwetting, is involuntary urination while asleep after the age at which bladder control usually begins. Bedwetting in children and adults can result in emotional stress. Complications can inc ...
(bed-wetting) . However, given females have a similar phenomenon called
nocturnal clitoral tumescence, prevention of nocturnal enuresis 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 (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 or penile glans, commonly referred to as the glans, (; from Latin ''glans'' meaning "acorn") is the bulbous structure at the Anatomical terms of location#Proximal and distal, distal end of the human penis ...
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 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 is used by
sexual health practitioners to ascertain whether a given case of erectile dysfunction is
psychological
Psychology is the scientific study of mind and behavior. Its subject matter includes the behavior of humans and nonhumans, both consciousness, conscious and Unconscious mind, unconscious phenomena, and mental processes such as thoughts, feel ...
or
physiological
Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...
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.
Nocturnal penile tumescence testing
Regularly, those who experience
erectile dysfunction
Erectile dysfunction (ED), also referred to as impotence, is a form of sexual dysfunction in males characterized by the persistent or recurring inability to achieve or maintain a Human penis, penile erection with sufficient rigidity and durat ...
are given a nocturnal penile tumescence 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
physiological
Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...
cause is usually suspected.
See also
*
Nocturnal emission
A wet dream, sex dream, or sleep orgasm, is a spontaneous occurrence of sexual arousal during sleep that includes ejaculation (nocturnal emission) and orgasm for a male, and vaginal lubrication and/or orgasm for a female.
Context
Nocturnal e ...
*
Priapism
*
Sleep sex
*
Swelling
*
Tumescence
References
Further reading
*
External links
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{{SleepSeries2
Andrology
Penile erection
Sleep