Any way you look at it, orgasm is an incredible bodily process, and one of the most intense sensory experiences our brains can go through. That goes for bodies too: blood rushes, breathing quickens, muscles contract. "It's basically all systems go at orgasm," says Barry R. Komisaruk, a professor of psychology at Rutgers University. In the name of taking some of the mystery out of one of the most interesting parts of our biology, here's how it all goes down.
Step 1: Excitement
Whether it's a sext, a caress, or a passing fantasy, some arousing experience is the first step toward potential orgasm. During this stage, the parasympathetic nervous system — known for its role in rest and recuperation — is activated. This causes the spongy tissue of the penis to become erect and is also what begins vaginal lubrication and the swelling of the labia in women. It also produces engorgement of the clitoris.
Step 2: Stimulation
A region of the brain located between the halves of the cortex called the genital sensory complex,is a main player in these initial stirrings. "When the stimulation starts, that part of the brain is what responds," says Komisaruk. Various sexual sensations reach this region, including penile, scrotal, and testicular touching in men. Although the extent to which the vagina and cervix are sensitive is hotly debated, Komisaruk's research has found that vaginal, cervical, and nipple stimulation all activate areas of the genital sensory complex in women. The pudendal, pelvic, hypogastric, and vagus nerves help communicate between the brain and the different genital areas.
The amygdala, hypothalamus, hippocampus, and frontal cortex also show increased activity during sexual excitement. The amygdala is involved in emotional response, the hypothalamus secretes oxytocin, and the hippocampus (which we usually associate with memory) may play a part in fantasy, along with the frontal cortex.
At some point, the sympathetic system (associated with fight or flight) kicks in and takes over. Heart rate, blood pressure, and sweating increase. Pupils dilate. During the excitement phase, women's breasts and vaginal walls swell. Men's testicles swell, the scrotum tightens, and the tip of the penis lubricates. These actions all continue into the plateau phase as well.
Step 3: Preparation
During this part of the sexual response cycle, the processes that began in the excitement stage continue. Erection and lubrication are maintained. In men, the testicles draw close to the body in preparation for ejaculation. In women, the vaginal walls darken and the increasingly sensitive clitoris often retracts under the clitoral hood to prevent direct stimulation. More areas of the brain light up. Activation of the cerebellum is responsible for muscle tension and may be the cause of muscle twitching at this stage.
Step 4: Orgasm
Climax is the shortest of all of the phases, and the one where the brain goes all out. "We see in men and women that the greatest activity in the brain occurs at orgasm," says Komisaruk. The hypothalamus, which builds in activity throughout this process, secretes oxytocin in maximum amounts during orgasm. This causes pleasurable contractions of the uterus that many women associate with orgasm and may facilitate ejaculation through contraction of the prostate and seminal vesicles. While we know oxytocin plays a role in physical functions, we are less sure about its emotional effects — contrary to what you've probably heard. "The 'cuddling hormone' idea is based on studies with rodents," says Komisaruk. "It's very controversial what oxytocin actually does perceptually in humans."
The nucleus accumbens revs up as well during this sensory explosion, contributing supreme feelings of gratification. "That has been described as the pleasure center in the brain," says Komisaruk. "It's activated by not only orgasm but also by cocaine and nicotine and caffeine and chocolate." This area receives dopamine from the ventral tegmentum. During orgasm, the dopamine system in the brain also maxes out.
One mystery of brain activity in this stage involves the insular cortex and anterior cingulate cortex. "Those two regions we see very strongly during orgasm in men and women," says Komisaruk. "Those two regions are also activated during pain." This similarity is something of a mystery. Komisaruk thinks this likeness may have to do with either the inhibition of pain or may be related to facial expressions, which are comically similar during pain and orgasm.
We know that men almost always ejaculate during orgasm. Some women do as well. This is not to be confused with squirting, which produces a chemically different fluid. As with men, female ejaculation is produced via activation of the sympathetic nervous system and the fluid comes from the female prostate gland and is chemically similar to semen.
Step 5: Resolution
After orgasm, the body does what it can to return to a pre-arousal state. Heart rate, breathing, and blood pressure slow back down. Genital swelling, including erection, reduces. Most people feel an extreme sense of relaxation, and men often get sleepy.
For the most part, the processes that go on in male and female bodies throughout orgasm look a lot alike. "The similarities between men and women during orgasm in the brain are much greater than the differences," says Komisaruk. The big caveat seems to be the refractory period. While many women can begin to build to orgasm again right after their last one, many men have to wait awhile. Komisaruk says he studied one man who was able to have six ejaculations in half an hour but, for most, a half-hour or more of rest between orgasms is necessary. Komisaruk is currently studying the refractory period to see if it has any relationship to anorgasmia, the inability to have an orgasm.