13.5: Male Sexual Activity

Although the testes function continuously, many activities in other parts of the male system are largely restricted to periods of sexual activity. During these active periods, the chronological sequence in which these parts operate is different from their anatomic sequence. In keeping with Masters and Johnson's thorough description of human sexual response, which forms the basis for the following discussion of sexual activity, this chronological sequence can be divided into five phases. These phases are listed in Table 13.1 along with bodily changes that occur in almost all instances (universal changes) and changes that occur less frequently (common or occasional changes).

Different men are affected by diverse intensities and combinations of factors. Therefore, there is great heterogeneity in age-related changes in sexual activity. Additional heterogeneity occurs because for each man, each incident of sexual activity may vary as a result of conditions such as physical environment, partner's involvement, mood, and length of time since the last sexual experience.

Excitement Phase

The excitement phase involves the development and persistence of several changes. Sometimes this phase may last for only a few seconds, while at other times it may be extended for many minutes.

The first action during this phase is erection of the penis. This is accompanied by reflexive contraction of the muscular sphincters below the urinary bladder so that urine cannot leave the bladder and injure sperm cells. These developments may be completed within several seconds and may be sustained for many minutes. The onset of erection is accompanied by or shortly followed by secretion from the bulbourethral glands. These three changes are often accompanied by other bodily changes, some of which occur more commonly than others.

Plateau Phase

As sexual arousal increases during the excitement phase, peristaltic contractions of the epididymis and ductus deferens move sperm cells and fluids into the ejaculatory ducts; as the penis reaches peak erection, the plateau phase begins. This phase is often accompanied by increases in the bodily changes seen during the excitement phase. Other changes may also occur. Up to this point distractions or a reduction in sexual stimulation may cause reduced or complete loss of erection and reversal of all the other concomitant sexual response changes. Renewed sexual stimulation can restore the conditions of the plateau phase.

At the end of this phase muscle contractions in the seminal vesicles and prostate gland force their secretions into the ejaculatory ducts and urethra. Simultaneously, the external urinary sphincter relaxes, allowing the semen to flow into the urethra. The internal urinary sphincter contracts forcefully, preventing semen from entering the bladder and preventing urine from leaving the bladder and entering the urethra.

Orgasmic Phase

The expansion of the urethra by semen often gives the impression that loss of voluntary control of sexual activity is imminent, and within a few seconds it triggers the orgasmic phase. During this phase completely reflexive rhythmic peristaltic contractions of the urethra, the other ducts, and muscles at the base of the penis force the semen out of the urethra (ejaculation). The first few contractions are the strongest and occur at intervals of slightly less than 1 second. After the first few contractions, the rhythm slows and the force of contraction diminishes. These activities are often accompanied by extreme levels of pleasurable sensations, which are usually centered in the penis, and by increases in the other changes that occur during the excitement and plateau phases. They may be followed by widespread perspiration. The orgasmic phase may last for a number of seconds.

Resolution Phase

As the orgasmic phase subsides, the penis begins to become flaccid. From seconds to minutes may be required to achieve a completely flaccid state. All the other bodily changes that occur during orgasm also quickly diminish and gradually disappear. This return to resting conditions constitutes the resolution phase.

Refractory Period

The resolution phase is followed by the refractory period, during which erection of the penis and the accompanying changes cannot occur. This period may last a few minutes to many hours, after which erection and the other activities in the cycle of male sexual activity may occur again.