The Sexual-Response Cycle and Our Bodies (cont.)
Phase One: Excitement
This phase usually begins within 10 to 30 seconds after erotic stimulation, and can last anywhere from a few minutes to many hours.
Men: The penis becomes slightly erect. A man's nipples may also become erect.
Women: Vaginal lubrication begins. The vagina expands and lengthens. The outer lips, inner lips, clitoris and sometimes breasts begin to swell.
Both: Heart rate, blood pressure and breathing are all accelerated.
Phase Two: Plateau
The changes that started in the excitement phase continue to progress.
Men: The testes are drawn up into the scrotum. The penis becomes fully erect.
Women: The vaginal lips become puffier. The tissues of the walls of the outer third of the vagina swell with blood, and the opening to the vagina narrows. The clitoris disappears into its hood. The inner labia (lips) change color (although it's a bit hard to notice). For women who've never had children, the lips turn from pink to bright red. In women who've had children, the color turns from bright red to deep purple.
Both: Breathing and pulse rates quicken. A "sex flush" may appear on the stomach, chest, shoulders, neck or face. Muscles tense in the thighs, hips, hands and buttocks, and spasms may begin.
Phase Three: Orgasm
This is the climax of the cycle. It is also the shortest of the four phases, usually only lasting a few seconds.
Men: First, seminal fluid collects in the urethral bulb. This is when a man may have the sensation that orgasm is certain, or "ejaculatory inevitability." Next, semen is ejaculated from the penis. Contractions occur in the penis during the orgasmic phase.
Women: The first third of the vaginal walls contract rhythmically every eight-tenths of a second. (The number and intensity of the contractions vary depending on the individual orgasm.) The muscles of the uterus also contract barely noticeably.
Both: Breathing, pulse rate and blood pressure continue to rise. Muscle tension and blood-vessel engorgement reach a peak. Sometimes orgasm comes with a grasping-type muscular reflex of the hands and feet.
Phase Four: Resolution
This phase is a return to the normal resting state. It can last from a few minutes to a half-hour or longer. This stage is generally longer for women than men.
Men: The penis returns to its normal flaccid state. There is usually a refractory period, where it's impossible to orgasm again until a certain amount of time has passed. The amount of time varies among men by age, physical fitness and other factors.
Women: The uterus and clitoris return to their normal positions. Some women may be able to respond to additional stimulation with additional orgasms.