How does ejaculation occur?

You might imagine that ejaculation -- the release of seminal fluid from your body -- is limited to your penis, testicles, and other reproductive organs, but you’d be wrong. In fact, your nervous system plays a key role.

Some parts of sexual arousal fall within parasympathetic nervous system responses and other processes fall within sympathetic. The sympathetic nervous system controls your body’s stress-related functions like the “fight or flight” response, which allowed your caveman ancestors to battle or escape dangerous predators. (These days, you’re more likely to rely on your fight-or-flight response before a big meeting with your boss.) Your parasympathetic nervous system controls your “rest and digest” response -- lower blood pressure, a slower heartbeat, and other functions related to relaxation.

The process begins when you’re sexually aroused, often -- but not always -- from the direct physical stimulation of your penis during touching, rubbing, oral sex, or intercourse, for example. Your brain responds by sending signals to your lower spinal cord. You get an erection, thanks to your parasympathetic nervous system. As a result, the muscles in your prostate gland, seminal vesicles (both of which produce seminal fluid), and vas deferens (the tube that connects the testicles to the urethra) contract rhythmically, moving semen through those glands and the urethra and out of your body, a process controlled by the sympathetic nervous system. An orgasm is the sensation of pleasure you feel during ejaculation.