There are four phases in the sexual response cycle: I. excitation, II. plateau, III. orgasm, and IV. resolution (Masters, Johnson, &Kolodny, 1994). In men, phase I (excitation) is characterized by erection of the penis. Phase I
takes place more slowly in women and is characterized by the production of lubricating fluid in the vagina, an increase in the diameter of the clitoris, and increased congestion of the labia with blood. For both sexes, phase II (plateau) is marked by a rise in the blood congestion of the pelvis and a strong feeling of sexual tension. A "sex flush" colors the forehead, neck, and chest, sometimes extending to the abdominal area. Phase III (orgasm) occurs in two stages in men: a preejaculatory contraction of the muscles involved in ejaculation, and actual ejaculation. The same muscles are involved in the orgasms of women as those of men. During phase IV (resolution), which is usually completed more quickly in men than in women, the congestion of the blood vessels that occurred during the previous phases of the sexual response cycle decreases. After a time, the cycle can be repeated. The duration of this recovery, or refractory period, is generally longer for men than for women; some women are capable of having several orgasms in fairly rapid succession.
With aging, both sexes experience a decline in all four phases of the sexual response cycle. Be that as it may, most older adults continue to appreciate and enjoy sexual intercourse. The degree of enjoyment is not dictated by biological factors alone, but depends to a large extent on the closeness and compatibility of the relationship between the sexual partners and how often they have sexual intercourse.
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