Male ejaculation happens in two rapid phases: first the body assembles semen and moves it into position, then a series of muscular contractions forces it out. The whole process takes only a few seconds, but it involves a coordinated chain of signals between the genitals, spinal cord, and brain. Here’s what actually happens at each step.
The Two Phases of Ejaculation
Ejaculation isn’t a single event. It happens in two distinct stages, called emission and expulsion, that occur back to back.
During emission, sperm travels from the testicles to the prostate, where it mixes with fluids to become semen. The tubes that transport sperm (called the vas deferens) contract to squeeze this mixture toward the base of the penis. At the same time, a muscle at the opening of the bladder tightens shut, preventing semen from flowing backward into the bladder.
During expulsion, muscles at the base of the penis contract rhythmically, about once every 0.8 seconds, pushing semen out of the body in several pulses. This is the moment most people think of as “cumming.” The contractions are involuntary once they start, which is why ejaculation feels reflexive rather than controlled.
What Semen Actually Contains
Sperm makes up only about 1% to 5% of the fluid that comes out. The rest is a mixture of fluids from two main glands. The seminal vesicles contribute 65% to 75% of the total volume, providing a thick, fructose-rich fluid that nourishes sperm. The prostate adds another 25% to 30%, producing a thinner, slightly acidic fluid that helps sperm survive.
The World Health Organization considers a normal ejaculate volume to be at least 1.4 milliliters, roughly a quarter of a teaspoon. Volume varies from person to person and is influenced by hydration, how long it’s been since the last ejaculation, and age.
How the Nervous System Triggers It
Ejaculation is a spinal reflex, meaning it can be triggered even without input from the brain. Sensory nerves in the penis send signals to a cluster of specialized neurons in the lower spinal cord. These neurons connect directly to the motor nerves controlling the muscles responsible for expulsion. In animal studies, researchers have shown that stimulating the penis activates these spinal neurons and the ejaculation muscles even when the spinal cord is completely disconnected from the brain.
That said, the brain is heavily involved under normal circumstances. During orgasm, brain imaging studies show intense activation in a deep region at the junction of the midbrain and the area just above it, including structures tied to reward and pleasure processing. The reward center (a region called the ventral tegmental area) lights up significantly. Interestingly, part of the brain associated with fear and vigilance, the amygdala, actually decreases in activity during ejaculation, which may explain why orgasm feels like a moment of release or letting go.
What Happens Right After
Immediately after ejaculation, most men enter a refractory period where further arousal and orgasm are temporarily impossible. Several things happen at once to create this cooldown. Dopamine, the brain chemical that drives sexual motivation, drops sharply in the brain’s reward and arousal centers. At the same time, signaling compounds in the peripheral nervous system dampen the body’s responsiveness to sexual stimulation.
In younger men, the refractory period can last just a few minutes. With age, it gradually lengthens, and 12 to 24 hours may pass before full arousal is possible again. Sexual function tends to shift most noticeably around age 40. The refractory period is one of the clearest biological differences between male and female sexual response, since many women don’t experience one at all.
When Ejaculation Works Differently
Not every ejaculation follows the standard pattern. In retrograde ejaculation, the bladder neck muscle doesn’t close properly during the emission phase, so semen travels backward into the bladder instead of out through the penis. A person with retrograde ejaculation still feels an orgasm, but little or no fluid comes out. The semen is harmlessly expelled later during urination.
Common causes include nerve damage from diabetes, multiple sclerosis, or spinal cord injuries. Certain surgeries involving the prostate or bladder can also affect that muscle, as can some medications for high blood pressure, prostate enlargement, and depression. Retrograde ejaculation isn’t dangerous, but it’s the reason some men notice a “dry orgasm” and is a recognized cause of fertility difficulties.
Factors That Affect the Experience
Several things influence how ejaculation feels and how much fluid is produced. Arousal time plays a role: longer foreplay and edging (approaching orgasm and then backing off) tend to produce stronger contractions and a more intense sensation. Hydration and overall health affect volume. Pelvic floor muscle strength matters too, since those are the muscles doing the contracting during expulsion. Exercises that strengthen the pelvic floor can lead to stronger, more defined contractions over time.
Frequency also matters. Ejaculating multiple times in a short window typically reduces volume with each successive orgasm, because the glands need time to replenish their fluids. After a few days of abstinence, volume tends to be higher. None of these variations are cause for concern. They’re simply reflections of the body’s normal fluctuation in fluid production and muscular response.