The second basic male sexual function is ejaculation—the process by which semen is expelled through the penis to the outside of the body. Many people equate male orgasm with ejaculation. However, these two processes do not always take place simultaneously. Before puberty a boy might experience hundreds of "dry orgasms"—orgasms without any ejaculation of fluid. Occasionally, a man may have more than one orgasm in a given sexual encounter, with the second or third orgasm producing little or no expelled semen. Thus, although male orgasm is generally associated with ejaculation, these two processes do not necessarily occur together.
From a neurophysiological point of view, ejaculation—like erection—is basically a spinal reflex (Truitt & Coolen, 2002). Effective sexual stimulation of the penis (manual, oral, or coital) results in the buildup of neural excitation to a critical level. When a threshold is reached, several internal physical events are triggered.
The actual ejaculation occurs in two stages (I Figure 4.7, page 98). During the first stage, sometimes called the emission phase, the prostate, seminal vesicles, and ampulla (upper portions of the vas deferens) undergo contractions. These contractions force various secretions into the ejaculatory ducts and prostatic urethra. At the same time, both internal and external urethral sphincters (two muscles, one located where the urethra exits the bladder and the other below the prostate) close, trapping seminal fluid in the urethral bulb (the prostatic portion of the urethra, between these two muscles). The urethral bulb expands like a balloon. A man typically experiences this first stage as a subjective sense that orgasm is inevitable, the "point of no return" or "ejaculatory inevitability."
In the second stage, sometimes called the expulsion phase, the collected semen is expelled out of the penis by strong, rhythmic contractions of muscles that surround the urethral bulb and root of the penis. In addition, contractions occur along the entire urethral route. The external urethral sphincter relaxes, allowing fluid to pass through, while the internal sphincter remains contracted to prevent the escape of urine. The first two or three muscle contractions around the base of the penis are quite strong and occur
Male Sexual Anatomy and physiology
Internal urethral — sphincter remains contracted
at close intervals. Most of the seminal fluid is expelled in spurts corresponding to these contractions. Several more muscle responses typically occur, with a gradual diminishing of intensity and lengthening of time intervals between contractions. The entire expulsion stage usually occurs in 3 to 10 seconds.
Some men have an experience known as retrograde ejaculation, in which semen is expelled into the bladder rather than through the penis. This results from a reversed functioning of the two urethral sphincters (the internal sphincter relaxes while the external sphincter contracts). The condition sometimes occurs in men who have undergone prostate surgery (Kassabian, 2003). In addition, illness, congenital anomaly, and certain drugs (most notably, tranquilizers and medications for high blood pressure) can induce this reaction (Mayo Clinic, 2008). Retrograde ejaculation itself is not harmful (the seminal fluid is later eliminated with the urine). However, a man who consistently experiences this response would be wise to seek medical attention, not only because the effective result is sterility but also because retrograde ejaculation could be a sign of an underlying health problem.
Sometimes a man experiences orgasm without direct genital stimulation. The most familiar of these occurrences are nocturnal emissions, which are commonly known as wet dreams. The exact mechanism that produces this response is not fully understood. (Women can also experience orgasm during sleep.) The possibility of a man using fantasy alone to reach orgasm in a waking state is exceedingly remote. Kinsey and his associates (1948) stated that only 3 or 4 of the males in their sample of over 5,000 reported
this experience. In contrast, significantly greater numbers of women in Kinsey’s sample (roughly 2%) reported orgasms from fantasy alone (Kinsey et al., 1953). Another kind of nongenitally induced ejaculation that men sometimes report is reaching orgasm during sex play (activities such as mutual kissing or manual or oral stimulation of his partner) when there is no penile stimulation.