Nocturnal penile tumescence

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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, morning glory or morning wood.[1] Men without physiological erectile dysfunction or severe depression[2] experience nocturnal penile tumescence, usually three to five times during a period of sleep, typically during rapid eye movement sleep.[3] Nocturnal penile tumescence is believed to contribute to penile health.[4]


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.[5] 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-related excitatory actions to manifest as nocturnal penile tumescence.[6] Suh et al. (2003) recognizes that in particular the spinal regulation of the cervical cord is critical for nocturnal erectile activity.[7]

The nerves that control a man’s ability to have a reflex erection are located in the sacral nerves (S2-S4) of the spinal cord.[8] Evidence supporting the possibility that a full bladder can stimulate an erection has existed for some time and is characterized as a 'reflex erection'.[9] 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[citation needed]. However, given females have a similar phenomenon called nocturnal clitoral tumescence, prevention of nocturnal enuresis (bed-wetting) is not likely a sole supporting cause.[10]

In an old study,[11] 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 old study of healthy aging men, frequency and duration of nocturnal penile tumescence decreased progressively with age independent of variations in sleep. In contrast to men in the younger age groups, the majority of men above age 60 did not have full sleep erections even though they and their partners reported regular intercourse.[12]

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.[13] SRPE, though also occur predominantly during REM sleep, without an apparent underlying illness are painful and thus interrupt sleep. 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 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.[14]

Diagnostic value[edit]

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.[3] 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.[3]

Nocturnal penile tumescence testing[edit]

Regularly, men who experience erectile dysfunction 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:

  1. a small portable computer connected to two bands placed around the shaft of the penis which records penile tumescence,
  2. 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 a man can experience an erection while sleeping after reporting he is unable to experience an erection while awake. The average man has 3–5 episodes of NPT each night, and each episode lasts 30–60 minutes, although the duration is reduced with advanced age.[15] If a man 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 a man does not obtain an erection in either state, a physiological cause is usually suspected.

See also[edit]



  1. ^ Schmidt, Markus H; Schmidt, Helmut S (March 2004). "Sleep-related erections: Neural mechanisms and clinical significance". Current Neurology and Neuroscience Reports. 4 (2): 170–178. doi:10.1007/s11910-004-0033-5. PMID 14984691. S2CID 26939007.
  2. ^ Thase, Michael E.; Reynolds, Charles F.; Jennings, J. Richard; Frank, Ellen; Howell, Joseph R.; Houck, Patricia R.; Berman, Susan; Kupfer, David J. (1988-05-01). "Nocturnal penile tumescence is diminished in depressed men". Biological Psychiatry. 24 (1): 33–46. doi:10.1016/0006-3223(88)90119-9. ISSN 0006-3223. PMID 3370276. S2CID 24315629.
  3. ^ a b c "Tests for Erection Problems". WebMD, Inc. Retrieved 2007-03-03.
  4. ^ Why guys rise and, well, rise in the morning?, The Body Odd, NBC News, October 2010
  5. ^ "SCI Fact Sheets - Spinal Cord Injury Model System | UAB".
  6. ^ Bancroft, J (2005). "The endocrinology of sexual arousal". Journal of Endocrinology. 186 (3): 411–427. doi:10.1677/joe.1.06233. PMID 16135662.
  7. ^ Suh, Donald; Yang, Claire; Clowers, Diane (2003). "Nocturnal penile tumescence and effects of complete spinal cord injury: possible physiologic mechanisms". Urology. 61 (1): 184–9. doi:10.1016/S0090-4295(02)02112-X. PMID 12559293.
  8. ^ Phil Klebine; Linda Lindsey (May 2007). "Sexual Function for Men with Spinal Cord Injury". Spinal Cord Injury Information Network. University of Alabama at Birmingham. Archived from the original on 2013-09-06. Retrieved 2011-12-17.
  9. ^ "Nervous system control of the male reproductive system". Retrieved 2018-01-09.
  10. ^ Scott Beale (Aug 2016). "Why Do Men Get Erections in the Morning". IFL Science. Retrieved 2016-12-03.
  11. ^ Karacan, Ismet; Hursch, Carolyn J; Williams, Robert L; Littell, Ramon C (June 1972). "Some Characteristics of Nocturnal Penile Tumescence during Puberty". Pediatric Research. 6 (6): 529–537. doi:10.1203/00006450-197206000-00001. PMID 4340042. S2CID 10758883.
  12. ^ Schiavi, R. C.; Schreiner-Engel, P. (1 September 1988). "Nocturnal Penile Tumescence in Healthy Aging Men". Journal of Gerontology. 43 (5): M146–M150. doi:10.1093/geronj/43.5.m146. PMID 3418036.
  13. ^ Johnson, Mark; McNeillis, Venkata; Gutbier, Julia; Eaton, Andy; Royston, Robert; Johnson, Thomas; Chiriaco, Giovanni; Walkden, Miles; Ralph, David (13 August 2021). "Differences in polysomnographic, nocturnal penile tumescence and penile doppler ultrasound findings in men with stuttering priapism and sleep-related painful erections". International Journal of Impotence Research: 1–7. doi:10.1038/s41443-021-00462-3. PMID 34389802. S2CID 236993535.
  14. ^ Podolej, GS; Babcock, C (January 2017). "Emergency Department Management Of Priapism". Emergency Medicine Practice. 19 (1): 1–16. PMID 28027457.
  15. ^ Bella, Anthony J.; Lue, Tom F. (12 December 2007). "Male Sexual Dysfunction". In Tanagho, Emil A.; McAninch, Jack W. (eds.). Smith's General Urology (17th ed.). McGraw Hill Professional. pp. 589–. ISBN 978-0-07-159331-1.


  • Knight, Jane (November 2016). The Complete Guide to Fertility Awareness. Routledge. ISBN 978-1138790100.