Ejaculation is the ejecting of semen from a penis, and is usually accompanied by orgasm. It is usually the final stage and natural objective of sexual stimulation, and an essential component of natural conception. In rare cases ejaculation occurs because of prostatic disease. Ejaculation may also occur spontaneously during sleep (a nocturnal emission or "wet dream"). Anejaculation is the condition of being unable to ejaculate.
Phases
Stimulation
A usual precursor to ejaculation is the sexual arousal of the male, leading to the erection of the penis, though not every arousal nor erection leads to ejaculation. Penile sexual stimulation during vaginal, oral or anal sexual intercourse, or manual stimulation (masturbation) may provide the necessary stimulus for a man to achieve orgasm and ejaculation. There are wide variations in how long the sexual arousal needs to be before ejaculation occurs.
Premature ejaculation is the term used when ejaculation occurs before the desired time. If a man is unable to ejaculate in a timely manner after prolonged sexual stimulation, in spite of his desire to do so, it is called delayed ejaculation or anorgasmia. An orgasm that is not accompanied by ejaculation is known as a dry orgasm.
Ejaculation
When a man has achieved a sufficient level of stimulation, ejaculation begins. At that point, under the control of the sympathetic nervous system, semen containing sperm is produced. The semen is ejected through the urethra with rhythmic contractions.[1] These rhythmic contractions are part of the male orgasm. They are generated by the bulbospongiosus muscle under the control of a spinal reflex at the level of the spinal nerves S2-4 via the pudendal nerve. The typical male orgasm can last up to 17 seconds but may vary from a few seconds up to about a minute.
After the start of orgasm, pulses of semen begin to flow from the urethra, reach a peak discharge and then diminish in flow. The typical orgasm consists of 10 to 15 contractions. Once the first contraction has taken place, there is no way to voluntarily prevent ejaculation process (but orgasm can be prevented, depending on a variety of factors). The rate of contractions gradually slows during the orgasm. Initial contractions occur at an average interval of 0.6 seconds with an increasing increment of 0.1 seconds per contraction. Contractions of most men proceed at regular rhythmic intervals for the duration of the orgasm. Many men also experience additional irregular contractions at the conclusion of the orgasm.[2]
Ejaculation begins during the first or second contraction of orgasm. For most men the first spurt occurs during the second contraction. The first or second spurt is typically the largest and can contain 40 percent or more of the total ejaculate volume. After this peak the flow of each pulse diminishes. When the flow ends, the muscle contractions of the orgasm continue with no additional semen discharge. A small sample study of seven men showed an average of 7 spurts of semen (range between 5 and 10) followed by an average of 10 more contractions with no semen expelled (range between 5 and 23). This study also found a high correlation between number of spurts of semen and total ejaculate volume, i.e, larger semen volumes resulted from additional pulses of semen rather than larger individual spurts.[3]
Refractory period
Most men experience a refractory period immediately following an orgasm, during which time they are unable to achieve another erection, and a longer period again before they are capable of achieving another ejaculation. The duration of the refractory period varies considerably. Age affects the recovery time, with younger men typically recovering faster than older men, though not necessarily universally so, as there is great variation between individuals.
However, many men are able to achieve sufficient sexual stimulation immediately after ejaculation, and others may have refractory periods of less than 15 or 20 minutes. A short recovery period may allow them to seamlessly continue sexual play from one ejaculation to sexual stimulation in preparation for the next.
Volume
The force and amount of semen that will be ejected during an ejaculation will vary widely between men and may contain between 0.1 and 11 milliliters.[4] Adult semen volume is affected by the time that has passed since the previous ejaculation; larger semen volumes are seen with greater durations of abstinence. It is not clear whether frequent ejaculation increases[5], reduces[6] or has no effect[7] on the risk of prostate cancer. The duration of the stimulation leading up to the ejaculation can affect the volume.[8] Abnormally low volume is known as hypospermia, though it is normal for the amount of semen to diminish with age.
Quality
The number of sperm in an ejaculation also varies widely, depending on many factors, including the time since the last ejaculation,[9] age, stress levels,[10] and testosterone. An unusually low sperm count, not the same as low semen volume, is known as oligospermia, and the absence of any sperm from the semen is termed azoospermia.
Development
During puberty
The first ejaculation in males often occurs about 12 months after the onset of puberty, either through masturbation or nocturnal emission (wet dreams). This first semen volume is small. The typical ejaculation over the following three months produces less than 1 ml of semen. The semen produced during early puberty is also typically clear. After ejaculation this early semen remains jellylike and, unlike semen from mature males, fails to liquefy. A summary of semen development is shown in Table 1.
Most first ejaculations (90 percent) lack sperm. Of the few early ejaculations that do contain sperm, the majority of sperm (97%) lack motion. The remaining sperm (3%) have abnormal motion.[11]
As the male proceeds through puberty, the semen develops mature characteristics with increasing quantities of normal sperm. Semen produced 12 to 14 months after the first ejaculation liquifies after a short period of time. Within 24 months of the first ejaculation, the semen volume and the quantity and characteristics of the sperm match that of adult male semen.[11]
| Time after first ejaculation (months) | Average volume (milliliter) | Liquification | Average sperm concentration (million sperm/milliliter) |
|---|---|---|---|
| 0 | 0.5 | No (1) | 0 |
| 6 | 1.0 | No (1) | 20 |
| 12 | 2.5 | No/Yes (2) | 50 |
| 18 | 3.0 | Yes (3) | 70 |
| 24 | 3.5 | Yes (3) | 80 |
Note 1 - Ejaculate is jellylike and fails to liquify.
Note 2 - Most samples liquify. Some remain jellylike.
Note 3 - Ejaculate liquifies within an hour.
Control from the central nervous system
To map the neuronal activation of the brain during the ejaculatory response, researchers have studied the expression of c-fos, a proto-oncogene expressed in neurons in response to stimulation by hormones and neurotransmitters.[12] Expression of c-fos in the following areas have been observed:[13][14]
- medial preoptic area (MPOA)
- lateral septum, bed nucleus of the stria terminalis
- paraventricular nucleus of the hypothalamus (PVN)
- ventromedial hypothalamus, medial amygdala
- ventral premammillary nuclei
- ventral tegmentum
- central tegmental field
- mesencephalic central gray
- peripeduncular nuclei
- parvocellular subparafascicular nucleus (SPF) within the posterior thalamus
Health issues
For most men, no detrimental health effects have been determined from ejaculation itself or from frequent ejaculations, though sexual activity in general can have health or psychological consequences. Some men experience a transient Post Orgasmic Illness Syndrome following ejaculation.
In one study, more frequent ejaculation earlier in one's life predicted lower rates of prostate cancer later on. Researchers have proposed that ejaculation may "flush out" carcinogens that accumulate in the prostate. However, no definitive reason for the link has been found, nor has it been proven that ejaculation is the direct cause of the reduced risk (but because the ejaculation occurred many years before cancer developed, it is not just that cancer causes reduced ejaculation).
The researchers note that increased sexual activity can increase the risk of sexually transmitted infections. Gathering direct experimental evidence for the ability of increased ejaculation to reduce cancer risk many years later would be extremely challenging.
See also
- Aspermia
- Azoospermia
- Coitus interruptus
- Coitus reservatus
- Cum shot
- Delayed ejaculation
- Female ejaculation
- Fertilization
- Keri - ejaculation in Jewish law
- Pre-ejaculate
- Premature Ejaculation
- Post Orgasmic Illness Syndrome
- Retrograde ejaculation
- Seminophagia
References
- ^ Walter F. Boron, Emile L. Boulpaep, (2005). Medical Physiology: A Cellular and Molecular Approach. Philadelphia, PA: Elsevier/Saunders. ISBN 1-4160-2328-3.
- ^ Bolen, J. G., (1980-12-09). "The male orgasm: pelvic contractions measured by anal probe". Archives of Sexual Behavior (6): 503-21. doi:. PMID 7458658.
- ^ Gerstenburg, T. C. (1990). "Erection and ejaculation in man. Assessment of the electromyographic activity of the bulbocavernosus and ischiocavernosus muscles". British Journal of Urology 65 (4): 395–402. doi:. PMID 2340374.
- ^ Rehan N, Sobrero AJ, Fertig JW. (1975). "The semen of fertile men: statistical analysis of 1300 men". Fertility and Sterility 26 (6): 492-502. PMID 1169171.
- ^ Dimitropoulou, Polyxeni; Artitaya Lophatananon, Douglas Easton, Richard Pocock, David P. Dearnaley, Michelle Guy, Steven Edwards, Lynne O'Brien, Amanda Hall, Rosemary Wilkinson, Rosalind Eeles, Kenneth R. Muir (November 11 2008). "Sexual activity and prostate cancer risk in men diagnosed at a younger age" (in english). BJU International 103 (2): 178–185. doi:. OCLC 10.1111/j.1464-410X.2008.08030.x.
- ^ "Masturbation Cuts Cancer Risk". BBC News Online. 2003-07-16. http://news.bbc.co.uk/2/hi/health/3072021.stm. Retrieved on 2009-03-04., Giles GG, Severi G, English DR, Hopper JL. (2004). "Frequency of ejaculation and risk of prostate cancer". JAMA 292 (3): 329. doi:. PMID 15265846.
- ^ Leitzmann MF, Platz EA, Stampfer MJ, Willett WC, Giovannucci E. (2004). "Ejaculation frequency and subsequent risk of prostate cancer". JAMA 291 (13): 1578-86. doi:. PMID 15069045.
- ^ Pound N, Javed MH, Ruberto C, Shaikh MA, Del Valle AP. (2002). "Duration of sexual arousal predicts semen parameters for masturbatory ejaculates". Physiol Behav 76 (4-5): 685-9. doi:. PMID 12127009.
- ^ "Semen and sperm quality". Dr John Dean, netdoctor.co.uk. http://www.netdoctor.co.uk/menshealth/facts/semenandsperm.htm. Retrieved on 2009-03-04.
- ^ "Biological Basis of Heredity: Cell Reproduction". Dr. Dennis O'Neil, Behavioral Sciences Department, Palomar College, San Marcos, California. http://anthro.palomar.edu/biobasis/bio_2.htm. Retrieved on 2009-03-04.
- ^ a b Janczewski, Z. and Bablok, L. (1985). "Semen Characteristics in Pubertal Boys". Archives of Andrology 15: 199–205. doi:. PMID 3833078.
- ^ Sagar SM, "et al." (1988). "Expression of c-fos protein in brain: metabolic mapping at the cellular level". Science 240: 1328–1332. doi:. PMID 3131879.
- ^ Pfaus JG and Heeb MM, (1997). "Implications of immediate-early gene induction in the brain following sexual stimulation of female and male rodents". Brain Res Bull 44: 397-407. doi:. PMID 9370204.
- ^ Veening JG and Coolen LM, (1998). "Neural activation following sexual behavior in the male and female rat brain". Behav Brain Res 92: 181-193. doi:. PMID 9638960.
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