Understanding sexual response Modeling human sexual response Sexual dissatisfaction and disorders in sexual relations are usually described as sexual dysfunctions. This can be misleading in its implication that someone is ‘dysfunctional’ and can pathologize normal variations in sexual response. A more holistic understanding is achieved by analyzing any sexual problems in the context of the sexual history of the individual or both parties in the relationship. (24) This is borne out by one study which found that the incidence of sexual dysfunction is largely situational and temporary. (25) In 1966 Masters and Johnson proposed a linear model for human sexual response, based on the assumption that men and women have similar sexual response. (31) This original model has since been built on by other authors as knowledge and understanding of the human sexual response has evolved. (26-30) Many women do not move through the phases sequentially, or even experience all of them. For example, they may move from sexual arousal to orgasm, without experiencing desire, or conversely experience arousal and desire, but not orgasm. (32) This can be conceptualized through a circular response model, as featured opposite, where different phases are incorporated alongside the linear response. (35) Men tend to follow the more linear, goal orientated model of desire, arousal and orgasm. (33)   Desire Is a strong need for sexual stimulation which occurs in the mind rather than the body. It may not move into the next phase without further psychological or physical stimulation. (34)   Arousal/excitation  Is marked by increased heart rate and blood pressure. It can be induced by image, fantasy, memory or sensory stimulus. This will facilitate the physiological changes such as increased blood flow to the genital organs, vaginal dilatation and lubrication, and erection in the man. (34)   Plateau/late stage excitation At this stage the sexual flush deepens and the muscle tension increases. The areolae around the nipples becomes larger. The labia continue to swell and the lower vagina swells, narrows and tightens. This stage is the highest moment of sexual arousal before orgasm; it may be achieved, lost and regained several times. (34)   Resolution  Is characterized by satisfaction, relaxation (decreased blood flow to the sex organs, relaxation of muscle tone). (34)