How Erection and Semen Release Occur

Erection and semen release are part of the male sexual response. Sexual stimulation can come from physical touch, sight, or sound. These signals activate a parasympathetic reflex in the sacral region of the spinal cord. The reflex causes nitric oxide, or NO, to be released. NO widens the arterioles in the penis and increases...

In response to the sexual stimuli, the parasympathetic neurons stimulate the local release of nitric oxide, or NO, dilating the arterioles in the penis. This increases blood flow into the erectile tissues — the corpora cavernosa and corpus spongiosum.

The blood filling the erectile tissues compresses the veins to prevent blood from leavin...