Erection means that the penis changes from a soft state to a hard state.

The erectile mechanism is mainly due to some sexual stimulation of the higher nerve center of the brain, such as vision, hearing, thinking or sexual hallucinations, which then causes the excitement of the erectile center at the bottom of the spinal cord, and then spreads to the reproductive organs along the sympathetic nerve, which expands the penile arterioles, increases blood flow, causes local congestion, increases internal pressure, and blocks venous return, resulting in the penis thickening and maintaining a firm state.

Penile erection caused by cerebral cortex excitement is called mental erection (or cerebral erection), which mostly occurs in young people. Because the sexual organs are stimulated, their impulses spread from the pudendal nerve to the sacral spinal erection center, which in turn led to congestion and hardening of the penis. It's called reflex erection. The above two kinds of erections can occur successively, and can also strengthen each other's erectile function.

When does the penis erect?

Before puberty, the penis occasionally erects. After puberty, your sexual feelings are more intense. Your penis often gets erect, sometimes many times a day.

The penis may erect under the following circumstances:

1. Wake up in the morning or hold your urine-too much urine oppresses your bladder.

2. Pants rub against penis during exercise.

3. Produce ideas related to sex, read books related to sex, fantasize, watch scenes in movies, etc.

4. Many times, erection will be accompanied by sexual arousal, such as you or others touching or pinching penis or scrotum in a sexual way.

5. The penis spontaneously erects for no reason. This situation is very common among adolescent boys.