A human sexual response cycle is  the overall period during which people are sexually stimulated and have sex with one another.

Sexual response stages are similar in both females and males but not identical. It means that, while the stages or phases in both genders are more or less same in sequence and general features, they do differ in mechanism and some other characteristics.

Following is a general overview of human sexual response cycle and mostly represents those features that are considered to be common or similar in both sexes.  One should, however, keep in mind; these stages are variable, and very individual. Although men & women will progress through the stages in order, the amount of time spent in each stage can vary dramatically.

1. Excitement (Desire):  Excitement is the first phase of sexual arousal during which the pulse rate increases, blood pressure rises, breathing quickens, and the skin may show a rosy flush (especially in females). This stage can last anywhere from a few minutes to several hours. Sexual activity during this stage is often called foreplay. Extending foreplay can sometimes make the other stages more intense.

Phase 1 further consists of 3 components: sexual drive, sexual motivation, and sexual wish. These reflect the biologic, psychological, and social aspects of desire, respectively. Sexual drive is produced through psychological and hormonal mechanisms. Drive is also highly influenced by hormones, medications (e.g., decreased by antihypertensive drugs, increased by dopaminergic compounds) and legal and illegal substances (e.g., alcohol, cocaine).

The most important characteristics of this phase of human sexual cycle is vasocongestion. It is defined as the accumulation of blood in the pelvic area during early sexual arousal contributes to erection of the penis in males (& of clitoris in females). The degree of erection during this phase depends on the intensity of sexual stimuli.

In males, routing of blood to the penis requires a working nervous system and the body to be relaxed enough and free from anxiety. Constriction of blood vessels, due to stress or anxiety, does not allow enough blood to enter the penis to cause an erection.  During an erection, the inner diameter of the urethra doubles and the scrotum pulls toward the body.

Similarly, muscular tension increases in the body. Heart rate and blood pressure both increase. It is normal for men to experience periods when the erection is lost during sex play, but then regained.  Distraction can lead to loss of excitement and erection. Emotional or mental well-being can affect desire, excitement/arousal and therefore, erectile functioning. For example, depression is associated with increased sexual problems.

2. Arousal (plateau):  It is second phase of sexual arousal during which the physical changes that began in the first phase are continued. Arousal is brought on by psychological and/or physiological stimulation. Multiple functional changes occur in men and women that prepare them for orgasm. In men, increased blood flow causes erection, penile color changes, and testicular elevation. In women, it leads to vaginal lubrication, clitoral tumescence, and labial color changes. In general, heart rate, blood pressure, and respiratory rate.

In males, the penis increases in size slightly during second stage of sexual response, particularly toward the glans or “head.” It is less likely for a man to lose his erection if distracted during plateau phase than during excitement. The testes increase in size by 50 percent or more and become elevated toward the body. Muscular tension heightens considerably and involuntary body movements increase as orgasm approaches.  Heart rate increases to between 100-175 beats per minute.

Usually during the plateau phase, a man will notice a small amount of clear fluid at the opening of the urethra that is released from the Cowper’s gland. This is known as “pre-cum” and serves to change the Ph balance of the urethra so that sperm may survive. This pre-ejaculatory fluid may be released during the excitement phase, may vary with each man and each sexual act. The pre-ejaculatory fluid may contain Sexually Transmissible Diseases (STD’s) or, sometimes, sperm that has remained in the urethra from previous ejaculations.

3. Orgasm (climax): It is a series of rhythmic contractions of the muscles of the vaginal walls or the penis, also the third and shortest phase of sexual response. Phase 3, orgasm, is the shortest of all the four phases and may last between 3 and 25 seconds, with continued increase of breathing rate, heart rate (pulse), and blood pressure and the voluntary and involuntary contraction of many muscle groups. In men, ejaculation is perpetuated by the contraction of the urethra, vas, seminal vesicles, and prostate. Conversely, in women, the uterus and lower third of the vagina contract involuntarily. The sensation of orgasm is difficult to describe, but men and women appear to have similar experiences. Both men and women describe muscle contractions, feelings of warmth spreading through the genital area and throughout the body, feelings of lightness or falling, and intense pleasure and bliss.

In males, actual climax and ejaculation are preceded by a distinct inner sensation that orgasm is imminent. This is called ejaculatory inevitability. Almost immediately, the male senses that ejaculation cannot be stopped. The most noticeable change in the penis during orgasm is the ejaculation of semen. The muscles at the base of the penis and around the anus contract rhythmically, with intervals of about 0.8 second between the first three or four contractions.  Physiologically, the sensations of orgasm and the response of ejaculation are two separate functions. As such, a man can experience orgasm without ejaculation, or vice versa. However, these two functions most often occur at about the same time. Males often have strong involuntary muscle contractions through the body during orgasm and can exhibit involuntary pelvic thrusting. The hands and feet show spastic contractions and the entire body may arch backward or contract in a clutching manner.

4. Resolution: Resolution is the final phase of the sexual response in which the body is returned to a normal state. Immediately following ejaculation, the male body begins to return to its unexcited state. About 50% of the penile erection is lost right away, and the remainder of the erection is lost over a longer period of time. Resolution is a gradual process that may take as long as two hours.

However, the duration of this final phase is highly dependent on whether orgasm was achieved. If orgasm is not achieved, irritability and discomfort can result, potentially lasting for several hours. If orgasm is achieved, resolution may last 10 to 15 minutes with a sense of calm and relaxation. Respiratory rate, heart rate, and blood pressure return to normal.

Women can have multiple successive orgasms secondary to a lack of a refractory period. However, the vast majority of men have a refractory period following orgasm in which subsequent orgasm is not possible. In fact, on average, men in their late thirties cannot be re-stimulated for 30 minutes or more. Very few men beyond their teenage years are capable of more than one orgasm during sexual encounters. Having said that, most men feel sexually satiated with one orgasm.  Muscular tension usually is fully dissipated within five minutes after orgasm, and the male feels relaxed and drowsy.