5.5: The Sexual Response
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To truly understand how these parts function during sexual intercourse, we need to consider a research-based paradigm developed by Masters and Johnson years ago which they called the sexual response cycle. The sexual response cycle is a model that explains how most people experience three phases when they engage in sexual intercourse: excitement, plateau, and then orgasm.
Masters and Johnson are quick to point out that each individual has a unique and varied sexual response so much so that no two sexual encounters would be expected to be perfectly identical between the same people. Nevertheless, these three phases are very common among most people.
As sexual intercourse begins both males and females pass through three phases. Excitement phase is when blood flows to the pelvis bringing, more lymphatic fluid and plasma to the region. Because of hormonal and psychological stimuli there is generally swelling in the sexual parts. While this is happening, the plateau phase begins which is when more hormones are released, moisture increases, heart rate increases, intensity of sensory perception increases (touch, smell, sight, hearing, and taste). In the orgasm phase an electrical build up of energy is released that is associated with a rhythmic contraction of the pelvic floor muscles, the urinary and anal sphincters, and of various glands for males. This is called an orgasm. After the orgasm finishes, resolution eventually allows the sexual parts to return to pre-excitement conditions. These are almost identical in every way between males and females, except that there are differing sexual parts for each.
Thus, a sexual response in a typical female would typically follow a pattern similar to this one.
In the excitement phase, blood and lymphatic fluids increase swelling inside the vagina. Hormones are secreted which lead to a mild uterine contractions which raise the uterus away from the pubic bone. The labia swell and the clitoris becomes hard. The vaginal tissues secrete moisture and the vagina itself lengthens and expands slightly inward. The plateau phase begins as excitement continues. This causes the labia to become fully swollen, the clitoris to recede under the clitoral hood, and the uterus to become fully elevated (the hormone is called Oxytocin). The vagina is fully lengthened into the body, and, just before orgasm, lubrication ceases. During orgasm, the pelvis of the female experiences a series of contractions which occur every 8/10ths of second and can number anywhere from 1-20 or more in the sequence. The contractions include anal and urinary sphincter contractions, the smooth muscles in the inward portion of the vagina contraction, the puboccocceygeus muscle contraction, the uterine contractions which cause the uterus and cervix to dip down into the vagina, and general muscles contractions in the body.
Further, an electrical sensation surges from the clitoris radiating throughout the body and stimulates the pleasure centers of the brain and a release of the hormone called Oxytocin. When the orgasm ends, the body eventually returns to its pre-excitement state. In general, females have more capacity to experience more contractions over a longer period of time than do males.
Females have been found to have much more capacity for sexual intercourse than males. This means females can have more sexual intercourse, more often, and with more orgasms than can the average male.
The male anatomy is presented in Figure 4. The male has a penis which is comprised of 3 spongy-like tissue columns that engorges with blood during excitement. A cross-section of the penis shows two outer columns and one column on the underneath side. The average male penis is just that—average. About 4-6 inches reported by Masters and Johnson. Since the vagina is 3 inches in length and has very sensitive regions near the outside of the vagina and not so sensitive regions deeper inside, the average male can satisfy the average female in heterosexual intercourse. Urine passes from the urinary bladder and exits at the external urethral orifice at the tip of the penis. The penis is attached inside the body to the pubic bone.
Figure
\(\PageIndex{1}\). Male Reproductive and Sexual Anatomy, Cross-sectional View
There are two testicles inside a pouch called the scrotum. One testicle sits higher than the other. On the back of the testicle is a storage compartment where mature sperm end up before ejaculation. This is called the epididymis. There is a muscle called the dartos muscle (not shown) which elevates and lowers the testicle based on temperature and sexual pleasure. Sperm grow best at about 91 degrees Fahrenheit and most males are at about 98 degrees, so the dartos will raise and lower the testicles if in colder or warmer temperatures.
The testicles produce about 125-250,000,000 sperm every 3-4 days. More importantly, the testicles produce the sex-drive hormone called Testosterone. In males and females, higher levels of testosterone typically mean a higher sex drive (another similarity). The vas deferens will eventually carry the sperm from the epididymis out of the body during the orgasm. The prostate gland swells during excitement and fills with prostatic fluid. The seminal vesicle located above the prostate gland also swells and produces a fluid filled with natural sugars.
For males, in the excitement phase, blood and lymphatic fluids increase swelling inside the prostate, seminal vesicle, testicle, scrotum, and the penis. Hormones are secreted which lead to a higher volume of blood flowing into the spongy tissue columns of the penis than flow out. The penis erects this way (sometimes the penis will leak fluid and/or sperm before the orgasm, regularly referred to as pre-ejaculate or “pre-cum”). The scrotum and dartos muscle draw both testicles up toward the pubic bone pressing the epididymis upward. As stimulation continues the swelling and fluid production continues to increase.
The plateau continues until just before the orgasm. When orgasm begins for males the penis is most erect. Males reach a point of no return in their orgasms (females do not). The ejaculation of sperm and fluids will continue in males, regardless of continued or interrupted stimulation.
Females would experience an interruption of the orgasm when stimulation is interrupted. For males, the orgasm also includes a series of contractions which occur every 8/10ths of second and can number anywhere from 1-10. Most males will have 5-6.
The contraction includes: anal and urinary sphincter contractions; prostate and seminal vesicle contractions, dartos and scrotum contractions, pelvic floor muscle contractions; penile contractions; and a rhythmic sequence of these in such a way that the ejaculate is expelled from the body out through the penis. The sperm are released from the epididymis and travel through the vas deferens up and around the bladder then through the ejaculatory duct (where it picks up prostate and seminal fluids) and finally out of the penis. An electrical sensation surges from the prostate gland throughout the body and stimulates the pleasure centers of the brain and a release of the hormone called Oxytocin. For males and females Oxytocin brings a feeling of emotional connection.
After an orgasm, males may continue to experience an erection, but will have to wait a while for the central nervous system to reset before they can ejaculate or orgasm again. Most males wait less time when younger and more time when older. For males, an ejaculation during orgasm would be expected, but sometimes ejaculations happen with or without orgasms, and orgasms may happen without ejaculations.