During sex a bunch of things happen to your body: Your pupils dilate, your heart rate increases, as do your levels of the hormone oxytocin. Sweat glands open to help cool the body, breasts enlarge 25 percent and your nipple height increases a half-inch.

Infrared cameras also show increased blood flow to the lips, nose, and labia (do you see a connection to that flushed look you achieve with your lipstick and blush?). This all happens as the sexual stimuli build up to an orgasm.

Why do women have orgasms? From an evolutionary standpoint, this was one of the ways women could tell if a man would be a good lifelong partner. It could help women distinguish between a caring, patient man and a selfish, impatient one! Nonetheless, a female orgasm can be so subtle—some women don’t know they’ve had one. Here’s how it happens…

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During intercourse, bodily fluids come in handy for the perfect amount of slide and friction. Together with the sights, sounds and smells of sex, the stimulation of the clitoris, labia and breasts build to an intense physical sensation. This is precisely when your brain tells your muscles and vagina to contract. Why? To bring the penis deeper and increase the chance of sperm hitting their target: the egg. Some women even ejaculate in the process.

During orgasm, the uterus sucks up the semen into the uterus. This also causes hormones to increase contractions, again, helping move semen into the uterus. Women who orgasm between one minute before and 45 minutes after their partner’s ejaculation have a greater tendency to retain sperm, compared to those who don’t orgasm.

The female orgasm isn’t easy to describe. But we know one thing for sure: The brain is the main conductor of this symphony. It might involve different instruments, sometimes the G-spot (parallel to a gathering of nerves on the male prostate). Women don’t have a magic sex-me-here button, but rather a region of nerves, like those spread over the surface of the male prostate.

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As a woman’s reproductive organs develop in utero, the rudimentary prostate moves away, so the nerves end up on the vaginal wall. If you insert your index finger up into the vagina and make a “come here” movement, you’ll touch the G-spot region that exists in some women. It’s often not that sensitive, but it works for some!

Women can be stimulated to orgasm through the mouth, nipples and other parts of the body. This points to the complexity of the system, reinforcing that the biology of sex truly evolves within the brain. One theory is that sexual stimuli are carried from the cervix and uterus to the brain through the vagus nerve. This is one of the nerves stimulated during deep breathing and meditation.

QUIZ: Are You Satisfied with Your Sex Life?