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Sex
Response Cycle
Sex Response Cycle refers
to the set of physiological and emotional changes that lead to and
follow orgasm. Different researchers have constructed various models of
the phases of the sex response cycle. Usually, these models include
three, four, or five distinct phases, with the exact components of each
phase differing across models. Helen Singer Kaplan proposed the
Triphasic Concept of human sexual response involving three stages:
desire, excitement, and orgasm. In his book Human Sexual Response,
Lief described five sexual response phases: desire, arousal,
vasocongestion, orgasm, and satisfaction.
William
Masters and Virginia Johnson, prominent sex
researchers and therapists, suggested that there are four identifiable
phases in the sex response cycle: excitement, plateau, orgasm, and
resolution. Using various instruments designed to monitor changes in
heart rate and muscle tension, Masters and Johnson were able specify the
bodily changes that characterize each of these phases.
The first phase,
excitement, can last for just a few minutes or extend for several hours.
Characteristics of this phase include: an increasing level of muscle
tension, a quickened heart rate, flushed skin (or some blotches of
redness may occur on the chest and back), hardened or erect nipples, and
the onset of vasocongestion, resulting in swelling of the woman's
clitoris and labia minora and erection of the man's penis. Other changes
also occur. In the woman, the vaginal walls begin to produce a
lubricating
liquid, her uterus elevates and grows in size, and her breasts
become larger. At the same time, the woman's vagina swells and the
muscle that surrounds the vaginal opening, called the pubococygeal
muscle, grows tighter. These changes prepare the woman's body for orgasm
and were called the "orgasmic platform" by Masters and
Johnson. Additional changes in men include elevation and swelling of the
testicles, tightening of the scrotal sac, and secretion of a lubricating
liquid by the Cowper's glands.
The second phase, known
as the plateau, is characterized primarily by the intensification of all
of the changes begun during the excitement phase. During this period,
the woman's clitoris may become so sensitive that it is painful to the
touch. The plateau phase extends to the brink of orgasm, which initiates
the reversal of all of the changes begun during the excitement phase.
The peak of sexual
excitement is reached during the third phase. Involuntary muscle
contractions, heightened blood pressure and heart rate, rapid intake of
oxygen, sphincter muscle contraction, spasms of the carpopedel muscles
in the feet, and sudden forceful release of sexual tension characterize
the orgasmic phase. For men, orgasm generally climaxes in the
ejaculation of semen, which contains millions of sperm.
Ejaculation
consists of two steps. During the first phase, called the emission
phase, seminal fluid builds up in the urethral bulb of the
prostate
gland. As the fluid accumulates, the male senses he is about to
ejaculate. This is often experienced as inevitable and uncontrollable.
During the second phase, called the expulsion phase, the urinary bladder
closes to block the possibility of urine mixing with the semen. At this
point, muscles at the base of the penis begin a steady rhythmic
contraction that finally expels the semen from the urethral opening at
the head of the penis. For women, orgasm
also consists of rhythmic muscle contractions, in this case of the
uterus, at about the same pace as in men. Tightening of the woman's
muscles puts pressure on the man's penis and assists in male orgasm. For
both sexes, barring the presence of some form of sexual dysfunction,
orgasm is an intensely pleasurable experience. Indeed, some see it as
the most pleasurable experience possible.
In the final phase, the
resolution, the body returns to normal levels of heart rate, blood
pressure, breathing, and muscle contraction. Swelled and erect body
parts return to normal and skin flushing disappears. The resolution
phase is marked by a general sense of well being and enhanced intimacy
and possibly by fatigue as well. Many women are capable of a rapid
return to the orgasmic phase with minimal stimulation and may experience
continued orgasms for up to an hour. Males, especially as they age,
experience a refractory period of varying duration after orgasm. During
this period, men cannot achieve orgasm, although partial or full
erection may sometimes be maintained. The duration of the refractory
period can vary from just a few minutes to several days and there is
great variability in the length of the refractory period both within and
between men.
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Sex
