Anal Sex - Anatomy and Stimulation

Anatomy and Stimulation

The abundance of nerve endings in the anal region and rectum makes anal sex pleasurable for many men and women. "The opening and closing of the anus is controlled by the internal and external sphincter muscles (the most important muscles when engaging in anal sex). The sphincter muscle is a sensitive membrane with many nerve endings and thus the source of pleasure or pain."

In a male receiving partner, being penetrated can produce a pleasurable sensation due to the inserted penis rubbing or brushing against the prostate (also known as the "male G-Spot", "P-Spot" or "A-Spot") through the anal wall. This can result in pleasurable sensations and can lead to an orgasm in some cases. Prostate stimulation can produce a "deeper" orgasm, described by some men as more widespread and intense, longer-lasting, and allowing for greater feelings of ecstasy than orgasm elicited by penile stimulation only. The prostate is located next to the rectum and is the larger, more developed male homologue to the Skene's glands (which are believed to be connected to the female G-Spot).

The majority of women (70–80%) require direct clitoral stimulation to achieve orgasm. The clitoris is composed of more than the externally visible glans (head). With its glans or body as a whole estimated to have around 8,000 sensory nerve endings, more than any other part of the human body, the clitoris surrounds the vagina somewhat like a horseshoe and surrounds the urethra and anus as well; the vagina is flanked on each side by the clitoral crura, the internal "legs" of the clitoris, which are highly sensitive and become engorged with blood when sexually aroused. In addition to nerve endings present within the anus and rectum, women may find anal stimulation pleasurable due to these "legs" extending along the vaginal lips (labia minora) back to the anus. Indirect stimulation of the clitoris through anal penetration may also be caused by the shared sensory nerves; especially the pudendal nerve, which gives off the inferior rectal nerves and divides into two terminal branches: the perineal nerve and the dorsal nerve of the clitoris.

The Gräfenberg spot, or G-Spot, is a debated area of female anatomy, particularly among doctors and researchers, but it is described as being located behind the female pubic bone surrounding the urethra and accessible through the anterior wall of the vagina; it is considered to have tissue and nerves that are related to the clitoris. Besides the shared connections of the aforementioned sensory nerves, orgasm by stimulation of the clitoris or G-Spot through anal penetration is made possible because a thin membrane is all that separates the vaginal cavity from the rectal cavity, allowing for indirect stimulation. Only a small percentage of women are able to orgasm from this type of stimulation alone. Direct stimulation of the clitoris, G-Spot, or both, during anal sex can help some women to enjoy the experience and reach orgasm.

In pornography, anal sex is often presented as routine and painless, but according to Go Ask Alice! and other researchers, anal sex occurs "much less frequently" than other sexual behaviors and can be painful if not performed with care. The increase of anal activity among heterosexuals has been linked to the increase in anal pornography, and the association with dominance and taboo make anal sex appealing to people of all sexual orientations. Moreover, the opening of the anus (its sphincter) is usually tighter than a vagina, which can yield greater tactile pleasure for the man via his penis.

While each person's sphincter muscles react to penetration differently, the anal sphincter in general has delicate tissue that can tear, and the rectal mucous membrane provides insufficient lubrication for sexual penetration. Researchers say adequate lubrication, relaxation, and communication between sexual partners are crucial to avoid pain or damage to the anus. Ensuring that the anal area is clean and the bowel is empty (for both aesthetics and practicality) is also recommended.