The Masters and Johnson model of sexual response, established in 1966, outlines the four stages: excitement, plateau, orgasm, and resolution. It revolutionized our understanding of human sexual physiology and dynamics.
Excitement-
The first stage is triggered by physical and mental erotic stimuli such as; kissing, touching or viewing erotic images that leads to sexual arousal. During the excitement phase, the body prepares for sexual intercourse. People may experience an increased heart rate and breathing rate, a rising blood pressure, and often vasocongestion of the skin (aka the sex flush). In females this flush is sometimes seen over the whole body, it is also responsible for the darkening of the clitoris and walls of the vagina.
Plateau-
The period of sex prior to orgasm. In both sexes, there is increased circulation and heart rate, increased sexual pleasure with increased stimulation and further increased muscle tension. Respiration continues at an increased level. In females, the clitoris becomes extremely sensitive and withdraws slightly. Lubrication is continually produced and the vaginal wall muscles continue to tighten.
In females, the onset of vasocongestion results in the swelling of the clitoris, labia minora and vagina. The muscles surrounding the vaginal opening become tighter and the uterus elevates and grows in size. The vaginal walls begin to produce a lubricating liquid, and meanwhile the breasts increase slightly in size and the nipples become hardened and erect.
Orgasm-
The conclusion of the plateau phase. It is accompanied by quick cycles of muscle contraction in the lower pelvic muscles, which surround the anus and the primary sexual organs. Females may experience uterine and vaginal contractions and external ejaculation. Orgasms are often associated with other involuntary actions, such as; vocalisation, muscle spasms in other parts of the body, and a general euphoric sensation. Heart rate continues to increase.
Resolution-
Occurs after orgasm and allows the muscles to relax, blood pressure to drop, and the body to slow down from its excited state. The refractory period (during the resolution phase) is the timeframe in which women have been recorded to have the capacity for multiple orgasms.
