It is obvious that the processes occurring during intercourse are not only the reaction of the genitals, but also changes in the circulatory system, muscle contractions, and neurohumoral reactions. In other words, the sexual response to the pathogen affects the entire human body, all its systems. The human sexual reaction cycle describes the physiological and emotional state during any erotic stimulation (for example, sexual intercourse or masturbation). There are several models of the cycle of sexual reactions put forward by researchers at different times. They differ in the number of phases, but have many common points. For convenience, let’s analyze the most popular option proposed by William Masters and Virginia Johnson, well—known sexologists.

Arousal is the result of an impact (emotional or physical). Kissing, touching, reading erotic literature or watching videos, fantasies — all this generates arousal in the first phase. The peripheral nervous system receives the signal and sends it to the brain. The hypothalamus reacts to arousal — it transmits a signal to increase testosterone production. Nitric oxide and norepinephrine are released, which increase blood flow to the genitals. Muscle tension increases throughout the body. Breathing and heart rate increase, blood pressure rises. There may be spot-like redness of some areas of the skin (mainly the chest and neck). There is an influx of blood to the genitals, as well as to the mammary glands. In women, the clitoris and labia minora swell, the nipples thicken and rise, and the walls of the vagina begin to secrete a lubricating fluid. The uterus rises almost vertically, and the inner two-thirds of the vagina usually extend to its full length (from 7 to 10 cm). Men have an erection of the penis, and the diameter of the urethra increases. The skin of the scrotum tightens and thickens.

All physiological changes are intensified. The body is preparing for orgasmic discharge. The activity of the amygdala increases. It is responsible for the perception of visual images and emotions. Activity in the memory area decreases, perception is concentrated on the processes taking place. The intensity of breathing, heartbeat, and blood pressure continues to increase. Muscle spasms may occur in the feet, face, and hands. The tension in the muscles increases. In women, the vagina continues to swell from increased blood flow, and its walls turn dark purple. The periarticular circles and labia also continue to increase in size. The clitoris becomes highly sensitive. The bartholin glands secrete additional lubricant. The pubococcygeal muscle tightens, reducing the diameter of the vaginal opening. In men, the penis increases in diameter and reaches a full erection. The testicles increase in size and tighten to the body. Cooper’s glands secrete several drops of liquid secretions (pre-ejaculate). The secret lubricates the urethra for the passage of sperm through it and removes residual urine and impurities.

Peak sexual arousal and discharge. Different areas of the brain are involved: the amygdala (memory and emotions), the hypothalamus (unconscious body control), the anterior cingulate cortex (impulsivity and empathy), and the nucleus accumbens (feeling euphoric). It releases oxytocin (associated with feelings of trust and affection), dopamine (responsible for feelings of pleasure), prolactin (inhibits the action of dopamine) and serotonin (improves mood). Involuntary muscle contractions begin. Blood pressure, heartbeat, and respiration are at their highest levels with rapid oxygen absorption. The muscles of the feet spasm. There is a sudden and rapid weakening of sexual tension. A rash or “genital redness” may occur all over the body. In women, the muscles of the vagina contract. The uterus also contracts rhythmically. In response to contact (or later during orgasm without contact), the external anal sphincter may contract involuntarily. In men, the penis and urethra undergo contractions, which expel sperm — ejaculation occurs.

The body returns to its normal state. The muscles relax. Blood pressure decreases. The heart rate and breathing return to normal. The body slowly returns to its normal level of functioning, and its altered parts return to their original size and color. There is a general feeling of well-being and closeness. Men begin a refractory period during which repeated stimulation cannot bring them to orgasm. Women do not have this period, and after the first orgasm, with continued stimulation, a woman can return to the plateau phase and then have an orgasm again. This is not feasible for all women, but only for those who do not experience unpleasant or painful sensations after further stimulation.