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Individual differences |
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Biological: Behavioural genetics · Evolutionary psychology · Neuroanatomy · Neurochemistry · Neuroendocrinology · Neuroscience · Psychoneuroimmunology · Physiological Psychology · Psychopharmacology (Index, Outline)
- Main article: Male orgasm
Ejaculation is the ejecting of semen from the penis, and is usually accompanied by male orgasm. It is usually the result of sexual stimulation. Rarely, it is due to prostatic disease. Ejaculation may occur spontaneously during sleep (a nocturnal emission). Anejaculation is the condition of being unable to ejaculate.
Ejaculation has two phases: emission and ejaculation proper. The emission phase of the ejaculatory reflex is under 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, and sexual stimulation precedes it.
The beginning of emission is typically experienced as a "point of no return," also known as point of ejaculatory inevitability. The sperm then passes through the ejaculatory ducts and is mixed with fluids from the seminal vesicles, the prostate, and the bulbourethral glands to form the semen, or ejaculate. During ejaculation proper, the semen is ejected through the urethra with rhythmic contractions.
These rhythmic contractions are part of the male orgasm. They are generated by the bulbospongiosus muscle. The typical male orgasm lasts about 17 seconds but can 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 to 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.
- Semen content
Sertoli cells, which nurture and support developing spermatocytes, secrete a fluid into seminiferous tubules that helps transport spermatozoa 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.
Most men experience a lag time between the ability to ejaculate consecutively, and this lag time varies among men. Age also affects the recovery time; younger men typically recover faster than older men though not necessarily universally so as great variation between individuals is present. During this refractory period it is somewhat difficult to attain another ejaculation. However, many men are able to enjoy sexual stimulation immediately after ejaculation and have fairly short refractory periods on the order 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 one. 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.
- See also: Sexual stimulation
There are wide variations in how long sexual stimulation can last before ejaculation occurs.
When a man ejaculates before he wants to it is called premature ejaculation. 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.
The force and amount of ejaculate vary widely from male to male. A normal ejaculation may contain anywhere from 1.5 to 5 milliliters. Adult ejaculate volume is affected by the amount of time that has passed since the previous ejaculation; larger ejaculate volumes are seen with greater durations of abstinence. However, a recent Australian study has suggested a positive correlation between prostate cancer and infrequent ejaculation and/or prostate milking, which performs essentially the same function. That is, frequent ejaculation appears to reduce the risk of prostate cancer. Frequent ejaculation is more easily obtained and sustained over time with the aid of masturbation and it is these ejaculations which are important, not the mechanism. 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 ejaculate to diminish with age.
- Main article: Semen quality
The number of sperm in an ejaculation also varies widely, depending on many factors, including the recentness of last ejaculation , age, and stress levels , 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 ejaculate is termed azoospermia.
The commonly reported experience by most men is that each contraction is associated with a wave of sexual pleasure, especially in the penis and loins. The first and second convulsions are usually the most intense in sensation, and produce the largest volume of ejaculate and the greatest quantity of semen. Thereafter, each contraction is associated with a diminishing volume of semen and a milder wave of pleasure. From empiric observations the above described series of events likely applies to the great majority of men. However, as in the majority of human experiences there are also multiple variations and differences between individuals that are likely of no great significance. There is only a small amount of scientific research on this subject at this point.
The first ejaculation in males occurs about 12 months after the onset of puberty. 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.
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.
Control from the central nervous system controlEdit
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. Expression of c-fos in the following areas have been observed:
- 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
- Main article: Fertilization
- See also: Pre-ejaculate
During penile-vaginal heterosexual intercourse, the vagina can provide sexual stimulation to the penis resulting in orgasm and ejaculation. Other methods of sexual stimulation such as manual, oral and anal can bring about an ejaculation that itself is performed into or around the vagina. Normally, ejaculation is required for emission of sperm; if ejaculation happens while the penis is either near or within the woman's vagina, sperm can then travel into the uterus and fertilize an egg if present, impregnating the woman. However, almost all men produce some pre-ejaculate fluid when they are sexually stimulated, and this pre-ejaculate may contain sperm which can also lead to pregnancy. Sexual arousal sufficient for pre-ejaculate production can be entirely psychologic and does not need an erection. For this reason, coitus interruptus may still lead to unwanted pregnancies for couples engaging in vaginal intercourse if other forms of birth control are not used as well. See also artificial insemination.
The health benefits of ejaculation or the detriments of abstaining from ejaculation are not clearly elucidated. No detrimental effects of ejaculation have been determined and such are extremely unlikely to exist from an evolutionary perspective. No such thing as too frequent ejaculation is recognized medically and one cannot ejaculate "too much" or "too frequently". This must be differentiated from sex addiction which is an unhealthy harmful behavior present in either men or women, that may or may not involve ejaculation. Sexual addiction acts and behaviors can be performed without orgasm or ejaculation. Up to date, there has only been one study showing an association between ejaculation and health, specifically, prostate cancer. More frequent ejaculation was associated with lower rates of prostate cancer and lower rates of ejaculation were associated with higher rates of prostate cancer. A causative relationship between ejaculation and prostate cancer is extremely difficult to demonstrate despite multiple available plausible biologic explanations. It must be remembered that these explanations, most involving inflammatory markers, are only theoretical and hypothetical and simply help in our understanding of how things might work and are part of the scientific models we ascribe to these biological phenomena. No direct experimental evidence is currently available to link ejaculation to disease. The molecular and cellular experiments demonstrating causative links between inflammation and carcinogenesis only apply to the experimental conditions themselves and cannot yet be plausibly extended to whole organisms. Medical recommendations about altering ejaculatory frequency can not be currently made with sufficient scientific rigor and in practice are unlike to be carried out anyways.
- Coitus interruptus
- Coitus reservatus
- Delayed ejaculation
- Female ejaculation
- Premature ejaculation
- Retrograde ejaculation
- ↑ 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.
- ↑ 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.
- ↑ Swimming Toward Conception: The Semen Analysis. Focus on Fertility, American Infertility Association and Organon Pharmaceuticals USA Inc.
- ↑ Masturbation Cuts Cancer Risk. BBC News Online.
- ↑ Semen and sperm quality. Dr John Dean, netdoctor.co.uk.
- ↑ Biological Basis of Heredity: Cell Reproduction. Dr. Dennis O'Neil, Behavioral Sciences Department, Palomar College, San Marcos, California.
- ↑ 8.0 8.1 Janczewski, Z. and Bablok, L. (1985). Semen Characteristics in Pubertal Boys. Archives of Andrology 15: 199–205.
- ↑ Sagar SM, "et al." (1988). Expression of c-fos protein in brain: metabolic mapping at the cellular level. Science 240: 1328–1332.
- ↑ 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.
- ↑ Veening JG and Coolen LM, (1998). Neural activation following sexual behavior in the male and female rat brain. Behav Brain Res 92: 181-193.
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