Good morning, class. Today we’re going to talk about the human physiological response to sexual stimulation, otherwise known as the sexual response cycle, a term coined by William Masters and Virginia Johnson, two researchers who pioneered studies in sex.
Their 1966 work Human Sexual Response was fundamental in understanding human sexuality, specifically female response to arousal. According to their model, the sexual response cycle is divided into four phases: excitement, plateau, orgasm and resolution.
Excitement is phase one; it occurs as a result of exposure to any erotic physical or mental stimulation. During this stage, the body prepares itself for sex. Physiologically, this involves an increased heart rate, breathing rate, and a rise in blood pressure. Erection of the nipples is very common at this stage, along with flushing of the skin. Intense sweating has also been documented in this stage.
In men, this stage also involves an erection, the drawing of the testicles upward toward the perineum, and the tensing of the scrotum. In women, the labia majora (that is, outter lips) flatten and the labia minora (the inner lips) engorge and may protrude from the outter lips of the vagina. The clitoris also becomes engorged, much like a smaller penis. Stimulation at this stage leads to the general darkening in the color of the vagina and the production of lubrication.
Plateau follows excitement and precedes orgasm. During this phase, there is more blood circulation and the heart rate increases for both genders.
In men, this phase involves the contraction of the urethral sphincter, to prevent semen from mixing with urine and to guard against retrograde ejaculation. Testicles rise closer to the body and the secretion of pre-ejaculate is common.
In women, the nipples and labia increase in size further and more lubrication is secreted. The PC muscle, which runs from pubic bone to the coccyx on the floor of the pelvic cavity tightens, making the vaginal opening smaller and setting up the platform for orgasm. Involuntary vocalization is common for both men and women at this stage.
Orgasm comes next, characterized by fast cycles of muscle contraction in the lower pelvic muscles of both genders. During this phase, more involuntary vocalization is common, along with spasms of muscles and a sense of euphoria.
In men, ejaculation occurs at orgasm, though it’s possible to have “dry” orgasms or for men to ejaculate without experiencing orgasm. A dry orgasm shortens the refractory period (which we’ll get to soon), making it easier for men to achieve the sort of multiple orgasms that many women can achieve naturally. Multiple-orgasms have been reported for men who began masturbating or engaging in sexual activity before puberty, likely due to a lack of refractory period. In female children it is always possible to have multiple-orgasms, even after puberty. In men, this ability decreases following the first ejaculation.
Following orgasm, the muscles begin to relax and blood pressure drops. This is the refractory period, the last stage of the sexual response cycle. Men usually experience a refractory period that may range from minutes to a full 24 hours. Women tend to have a small refractory period, allowing them to return to the plateau stage with further almost immediately following an orgasm.
Information from Human Sexual Response.