Masters and Johnson, pioneering sex therapists, defined a classic sexual response cycle in the mid-1960s. The stages of this model are:Excitement/Arousal: The feeling that you want to have sex followed by physical changes that occur in your body as you become sexually excited. These include moistening of the vagina, relaxation of the muscles of the vagina; swelling of the labia (skin folds that are part of the vulva) and the clitoris (a small, sensitive organ above the vagina, where the inner labia, which surrounds the vagina, meet that acts as a source of sexual excitement). The nipples also become erect.Plateau: The above changes in the genitals continue, there is an increase in blood flow to the labia, the vagina grows longer, and glands in the labia produce secretions. There is an increase in muscle tension.Orgasm: Known as the peak of the sexual response, the muscles of the vagina and uterus contract leading to a strong, pleasurable feeling.Resolution: You return to your normal state.However, it's important to point out that more contemporary research suggests that women's sexual response is more complex and includes more elements than the traditional model outlines. Relationship and intimacy needs appear to play a greater role in women's sexual health. According to sexual health experts, a better understanding of the complexity of women's sexuality will help to more accurately diagnose and treat sexual dysfunction.