The sexual model that best fits the male sexual response is Masters and Johnson’s linear and quadriphasic: arousal, plateau, orgasm and resolution (Table 1), completed with the contribution of Helen Kaplan (1979), the phase of desire, prior to and independent of arousal.

Desire in the male

The appearance and maintenance is multifactorial, depending on internal stimuli (for example, biological factors or thoughts) or external (for example, the sight of an attractive partner). Androgen hormone levels are considered to play a key role in activating the normal male sexual response. During adolescence, testosterone levels are essential for sexual desire, but this influence is more relative at older ages.

Arousal phase, also called intumescence, whose duration can vary from minutes to hours. In it, the level of muscle tension increases, the heart rate and vasocongestion of the genital organs begins.
The onset of erotic sensations and/or stimulation cause global neurological, vascular, muscular and hormonal reactions in the body, the most evident being the anatomical and functional changes of the genitalia.

Vasodilatation phenomena give rise to penile erection and tumescence of other organs such as the testicles and internal genitalia. The prostate and the seminal vesicles increase their secretory activity, accumulating an appreciable volume of liquids that, mixed in time with the contents of the vas deferens, will form the ejaculate.

Plateau phase, lasts until orgasm and is of variable duration. Previous changes are intensified. The bladder closes to prevent urine from mixing with semen, and the muscles at the base of the penis contract rhythmically, eventually ejecting the semen.

Orgasm phase, the shortest of the phases, from 3 to 15 seconds. There are involuntary muscle contractions, such as the sphincter; blood pressure and heart and respiratory rates increase; and there is a sudden release of nervous tension. In men, orgasm is usually achieved with the ejaculation of semen. Initially seminal fluids accumulate in the urethral bulb of the prostate gland. As they build up, you feel that you are going to ejaculate, and that feeling is experienced as inevitable and uncontrollable.

Resolution or detumescence phase, the last stage where the physiological and anatomical changes that appeared in the three previous phases return to their basal state, with a variable subsequent refractory period.

Necessary conditions to achieve an erection:

• Adequate emotional state in the relationship with the couple and attitude towards sexuality that does not block the spontaneous physiological mechanisms that favor it.
• Sufficient psychogenic and reflexogenic stimulation.
• Indemnity in the anatomy of the penis, with adequate vascularization and innervation.
• Sufficient hormonal levels and good metabolic balance.

Facilitating agents

External sensory stimuli: Visualization of another or other people who conform to the canons of beauty, olfactory stimuli, etc. Pheromones activate sexuality in mammals, but there is not so much evidence about their influence in humans. Of all the senses, touch is the one with the greatest influence on the erection, having drawn up erotic maps of the most sensual points.

Internal stimuli
• Erotic fantasies.

• Sleep: While sleeping, a normal person has four or five periods of REM phase (rapid eye movement, lighter sleep and more dreaminess). Total REM sleep time per night is between 90 and 120 minutes in adults, and erections lasting 20 to 30 minutes are common.

• Personality: Those prone to erotophilia can be distinguished, who respond with positive emotions to sexual stimulation and tend to seek sensations and sexual stimuli, from those who have erotophobic tendencies, who respond with negative emotions and who, to a greater or lesser extent, extent, they avoid sexual sensations and stimuli.