Similarities and Differences between the sexes
The sexual response cycle is characterized by vasocongestion, swelling of the genital tissues with blood, and myotonia, muscle tension. Vasocongestion causes erection of the penis and swelling of the clitoris, labia, testes, nipples, and even the earlobes. Myotonia causes facial grimaces, spasms in the hands and feet, and finally, the spasms of orgasm.
The first phase is called the excitement phase. For men this phase is characterized by the erection of the penis, a thickening of the scrotal skin, and the enlargement and elevation of the testes. In women the clitoris and labia swell, the breasts enlarge, and vaginal lubrication is produced. Both sexes experience a slight flushing of the skin, increased blood pressure and heart rate, and erection of the nipples.
Next the body moves into the plateau phase when the level of sexual arousal remains fairly stable. Men in this phase experience the enlargement and elevation of the testes and an increase in the circumference of the head of the penis; which can often take on a purplish hue caused by the blood trapped by the swelling. A woman’s clitoris shortens; withdrawing beneath the hood, and the vaginal muscles begin to contract in preparation to hold the penis. Breathing speeds up and sounds more like panting, heart rate, and blood pressure continue to rise in both men and women.
During the orgasmic phase in males consists of two stages; first the bladder sphincter is closed as semen gathers at the base of the penis, then a series of three to seven muscle spasms cause the semen to be propelled down the shaft and out of the head of his penis. For a woman the number of pelvic muscle contractions is between three and fifteen at peak with weaker contractions as the orgasm ends. Blood pressure peaks with heart rates up to 180 beats per minute and breathing can increase to 40 breaths per minute.
Finally the body reached the resolution phase.
References: Rathus, S. A., & Nevid, J. S. (2002). Psychology and the Challenges of Life. Hoboken, NJ: John Wiley & Sons, Inc.. Web MD. (2010). Erectile Dysfunction Guide. Retrieved from http://www.webmd.com/erectile-dysfunction/guide/erectile-dysfunction-treatment-care