Human sexual response cycle
[3] Physical and emotional interaction and stimulation of the erogenous zones during foreplay usually establishes at least some initial arousal.
[4] Vasocongestion of the skin, commonly referred to as the sex flush, will occur in approximately 50-75% of females and 25% of males.
During the male sex flush, the coloration of the skin develops less consistently than in the female, but typically starts with the epigastrium (upper abdomen), spreads across the chest, then continues to the neck, face, forehead, back, and sometimes, shoulders and forearms.
In males, the beginning of the excitement phase is observed when the penis becomes partially or fully erect, often after only a few seconds of erotic stimulation.
Both testicles become drawn upward toward the perineum, notably in circumcised males where less skin is available to accommodate the erection.
The onset of vasocongestion results in swelling of the woman's clitoris, labia minora and vagina.
Orgasm is experienced by both males and females, ending the plateau phase of the sexual response cycle.
[clarification needed] Orgasms are often associated with other involuntary actions, including vocalizations and muscular spasms in other areas of the body and a generally euphoric sensation.
The resolution phase occurs after orgasm and allows the muscles to relax, blood pressure to drop and the body to slow down from its excited state.
In the second stage (and after the refractory period is finished), the penis decreases in size and returns to being flaccid.
[14][15] Masters and Johnson argue that, despite some minor differences, sexual responses in both men and women are fundamentally similar.
[2] These variations can pose problems because psychologists have argued that not everyone fits this model; for example, most women do not orgasm during penetrative sexual intercourse.
[16] Masters and Johnson also equate a man's erection with a woman's vaginal lubrication during the excitement phase; Roy Levin states that this observation is false.
Levin also presents research which shows that the first signs of physiological arousal in women is increased blood flow to the vagina, not lubrication.
[16][18] Rosemary Basson argues that this model poorly explains women's sexual response, especially for those who are in long-term relationships.
[16][27] Shortly after Masters and Johnson published their book, several scholars criticized their model of the human sexual response cycle.
For example, Helen Singer Kaplan argued that Masters and Johnson only evaluated sexual response from a physiological perspective, and that psychological, emotional, and cognitive factors need to be taken into consideration.
As a result, she proposed her model of the sexual response cycle which includes three phases: desire, excitement, and orgasm.
The model explains that the desire for sex comes from an interaction between a sensitive sexual response system and stimuli that are present in the environment.
[27] Other researchers have attempted to evaluate women's sexual functioning in terms of this new model but have found contradictory results.
[32] More research needs to be done in this area to show whether the circular model more accurately describes women's sexual response.
Recent research, however, suggests that the current model of sexual response needs to be revised to better treat these dysfunctions.
[37] Because of the high comorbidity rates between HSDD and FSAD, she would like to merge them to make the category "Sexual Interest/Arousal Disorder."
Hartmann and colleagues summarize their views of the current model of the sexual response cycle and conclude that "by simply expanding and continuing DSM-IV criteria and the traditional response cycle classification systems, it is impossible to come to diagnostic categories and subtypes that adequately reflect real-life female sexual problems".
