Ejaculation
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Ejaculation is the ejecting of semen, or more commonly know as cum, 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. Abstinence from discharge will normally result in a longer orgasm and more quantity.
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 sexual arousal is required 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
Ejaculation has two phases: emission and ejaculation proper. The emission phase of the ejaculatory reflex is under the control of the sympathetic nervous system, while the ejaculatory phase is under control of a spinal reflex at the level of the spinal nerves S2-4 via the pudendal nerve. A refractory period succeeds the ejaculation.
Emission
The emission stage marks the "point of no return," also known as point of ejaculatory inevitability. When emission starts, sperm pass through the ejaculatory ducts and mix with fluids from the seminal vesicles, the prostate, and the bulbourethral glands to form the semen, or ejaculate.
Ejaculation proper
During ejaculation proper, 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. 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, each bringing an extremely pleasurable sensation at the head of the penis. Once the first contraction has taken place, there is no way to voluntarily prevent ejaculation taking place. 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]
Volume
The force and amount of semen that will be ejected during an ejaculation will vary widely between men and may contain between 1.5 and 5 milliliters.[3] 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. There's contradiction of whether frequent ejaculation increases[4] or reduces[5] the risk of prostate cancer. Also, the duration of the stimulation leading up to the ejaculation can affect the volume. Abnormally low volume is known as hypospermia, though it is normal for the amount of semen to diminish with age.
Semen content
Sertoli cells, which nurture and support developing spermatocytes, secrete a fluid into seminiferous tubules that helps transport sperm to the genital ducts. The ductuli efferentes possess cuboidal cells with microvilli and lysosomal granules that modify the semen by reabsorbing some fluid. Once the semen enters the ductus epididymis the principle cells, which contain pinocytotic vessels indicating fluid reabsorption, secrete glycerophosphocholine which most likely inhibits premature capacitation. The accessory genital ducts, the seminal vesicle, prostate glands, and the bulbourethral glands, produce most of the seminal fluid. The seminal vesicles produce a yellowish viscous fluid rich in fructose and other substances that makes up ~70% of human ejaculate. The prostatic secretion, influenced by dihydrotestosterone, is a whitish (sometimes clear), thin fluid containing proteolytic enzymes, citric acid, acid phosphatase and lipids. The bulbourethral glands secrete a clear secretion into the lumen of the urethra to lubricate it.
Semen begins to spurt from the penis during the first or second contraction of orgasm. For most men the first spurt occurs during the second contraction. A small sample study of seven men showed between 26 and 60 percent of the contractions during orgasm were accompanied by a spurt of semen.[6]
Quality
The number of sperm in an ejaculation also varies widely, depending on many factors, including the time since the last ejaculation,[7] age, stress levels,[8] 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.
Refractory period
Most men experience a refractory period immediately following an orgasm, during which time they are unable to achieve another erection. The duration of this 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. This allows them to seamlessly continue sexual play from one ejaculation to another as afterplay and foreplay merge into each other. Thus, a refractory period is not an unwelcome interruption for sexual activity or a period of "forced full rest" but often a perfect opportunity to turn attention productively to one's sexual partner.
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 ejaculate 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. 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.[9]
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 liquefies 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.[9]
Control from the central nervous system control
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.[10] Expression of c-fos in the following areas have been observed:[11][12]
- 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 the majority of the population, no detrimental effects of ejaculation have been determined. Detrimental health effects related to ejaculation are extremely unlikely to exist from an evolutionary perspective. No such thing as too frequent ejaculation is recognized medically (though of course sexual behavior 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 backfire by increasing 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
- Post Orgasmic Illness Syndrome
- Retrograde ejaculation
References
- ^ Walter F. Boron, Emile L. Boulpaep, (2005). Medical Physiology: A Cellular and Molecular Approach. Philadelphia, PA: Elsevier/Saunders. ISBN 1-4160-2328-3.
{{cite book}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link) - ^ Bolen, J. G., (1980-12-09). "The male orgasm: pelvic contractions measured by anal probe". Archives of Sexual Behavior (6): 503–21. doi:10.1007/BF01542155. PMID 7458658.
{{cite journal}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link) - ^ "Swimming Toward Conception: The Semen Analysis". Focus on Fertility, American Infertility Association and Organon Pharmaceuticals USA Inc. Archived from the original on 2008-01-12.
- ^ Dimitropoulou, Polyxeni (November 11 2008). "Sexual activity and prostate cancer risk in men diagnosed at a younger age". BJU International. 103 (2): 178–185. doi:10.1111/j.1464-410X.2008.08030.x. OCLC 10.1111/j.1464-410X.2008.08030.x.
{{cite journal}}: Check|oclc=value (help); Check date values in:|date=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ "Masturbation Cuts Cancer Risk". BBC News Online. 2003-07-16. Retrieved 2009-03-04.
- ^ 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:10.1111/j.1464-410X.1990.tb14764.x. PMID 2340374.
- ^ "Semen and sperm quality". Dr John Dean, netdoctor.co.uk. Retrieved 2009-03-04.
- ^ "Biological Basis of Heredity: Cell Reproduction". Dr. Dennis O'Neil, Behavioral Sciences Department, Palomar College, San Marcos, California. Retrieved 2009-03-04.
- ^ a b Janczewski, Z. and Bablok, L. (1985). "Semen Characteristics in Pubertal Boys". Archives of Andrology. 15: 199–205. doi:10.3109/01485018508986912. PMID 3833078.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Sagar SM; et al. (1988). "Expression of c-fos protein in brain: metabolic mapping at the cellular level". Science. 240: 1328–1332. doi:10.1126/science.3131879. PMID 3131879.
{{cite journal}}: Cite has empty unknown parameter:|unused_data=(help); Explicit use of et al. in:|author=(help); Text "volume-240" ignored (help) - ^ 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:10.1016/S0361-9230(97)00219-0. PMID 9370204.
{{cite journal}}: CS1 maint: extra punctuation (link) - ^ 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:10.1016/S0166-4328(97)00190-3. PMID 9638960.
{{cite journal}}: CS1 maint: extra punctuation (link)
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