Orgasms and Nerves
A clitoral orgasm, for example, differs from a vaginal orgasm because different sets of nerves are involved.
All of the genitalia contain a huge number of nerve endings (the clitoris alone has more than 8,000 of them), which are, in turn, connected to large nerves that run up through the body to the spinal cord. (The exception is the vagus nerve, which bypasses the spinal cord.) They perform many other functions in the body in addition to providing the nerve supply, and therefore feedback to the brain, during sexual stimulation. Here are the nerves and their corresponding genital areas
hypogastric nerve - transmits from the uterus and the cervix in women and from the prostate in men
pelvic nerve - transmits from the vagina and cervix in women and from the rectum in both sexes
pudendal nerve - transmits from the clitoris in women and from the scrotum and penis in men
vagus nerve - transmits from the cervix, uterus and vagina
The role of the vagus nerve in orgasms is a new discovery and there's still much that's unknown about it; until recently, researchers didn't know that it passed through the pelvic region at all.
Since most of those nerves are associated with the spinal cord, it would stand to reason that a person with a severed spinal cord wouldn't be able to have an orgasm. And for a very long time, that's what people with these types of injuries were told. However, recent studies show that people with spinal cord injuries -- even parapalegics -- can reach orgasm. Dr. Barry Komisaruk and Dr. Beverly Whipple of Rutgers University conducted a study on women with severed spinal cords in 2004. They discovered that these women could feel stimulation of their cervixes and even reach orgasm, although there was no way their brain could be receiving information from the hypogastric or pelvic nerves. How was this possible? An MRI scan of the women's brains showed that the region corresponding to signals from the vagus nerve was active. Because the vagus bypasses the spinal cord, the women were still able to feel cervical stimulation.
So during sexual stimulation and orgasm, different areas of the brain receive all of this information that lets it know exactly what's happening -- and that what's happening is very enjoyable
Pleasure Center of the Brain: Light It Up
You may have heard that the brain has a pleasure center that lets us know when something is enjoyable and reinforces the desire for us to perform the same pleasurable action again. This is also called the reward circuit, which includes all kinds of pleasure, from sex to laughter to certain types of drug use. Some of the brain areas impacted by pleasure include:
amygdala - regulates emotions
nucleus accumbens - controls the release of dopamine
ventral tegmental area (VTA) - actually releases the dopamine
cerebellum - controls muscle function
pituitary gland - releases beta-endorphins, which decrease pain; oxytocin, which increases feelings of trust; and vasopressin, which increases bonding
Although scientists have long been studying the pleasure center, there hadn't been much research about how it relates to sexual pleasure, especially in women. In the late 1990s and the mid-2000s, a team of scientists at the University of Groningen in the Netherlands conducted several studies of both men and women to determine brain activity during sexual stimulation. The team used PET scans to illustrate the different areas of the brain that would light up and shut off during sexual activity. In all of the tests, the subjects were scanned while resting, while being sexually stimulated and while having an orgasm.
Interestingly, they discovered that there aren't too many differences between men's and women's brains when it comes to sex. In both, the brain region behind the left eye, called the lateral orbitofrontal cortex, shuts down during orgasm. Janniko R. Georgiadis, one of the researchers, said, "It's the seat of reason and behavioral control. But when you have an orgasm, you lose control" [source: LA Times]. Dr. Gert Holstege stated that the brain during an orgasm looks much like the brain of a person taking heroin. He stated that "95 percent is the same" [source: Science News].
There are some differences, however. When a woman has sex, a part of the brain stem called the periaqueductal gray (PAG) is activated. The PAG controls the "flight or fight" response. Women's brains also showed decreased activity in the amygdala and hippocampus, which deal with fear and anxiety. The team theorized that these differences existed because women have more of a need to feel safe and relaxed in order to enjoy sex. In addition, the area of the cortex associated with pain was activated in women, which shows that there is a distinct connection between pain and pleasure.
The studies also showed that although women may be able to fool their partners into thinking they've had an orgasm, their brains show the truth. When asked to fake an orgasm, the women's brain activity increased in the cerebellum and other areas related to controlling movement. The scans didn't show the same brain activity of a woman during an actual orgasm.
But what about people who can't reach orgasm at all?
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