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Sexual Response Cycle
The four stages of human sexual response. Based on observations and interviews with people, Masters and Johnson (1966) identified the following four stages. The first stage is the excitement phase, during which physical arousal increases quickly. This arousal is indicated by increased muscle tension, breathing, and heart rate, as well as increase in blood pressure. Due to vasocongestion, the enlargement of blood vessels, the penis erects, and the clitoris becomes harder and swells, while the vagina becomes lubricated. During the second stage, the plateau phase, physiological arousal still increases but at a notably reduced rate. For example, in women, the vaginal entry becomes tighter. The majority of men may secrete a small drop of fluid at the top of the penis. This drop may hold ...