This overall process starts with the brain registering a sexual stimulus. The brain then orchestrates a cascade of nerve signals that actually run all the way through the spinal cord to the penis. Here, the cavernosal nerves release nitric oxide this a gas that quickly penetrates to the smooth muscle cells that form the penis' spongy tissue. The nitric oxide causes the cells to produce a substance that in fact called the cyclic guanine mono phosphate (c GMP), which has an actually expansive, relaxing effect.

The arteries feeding the penis expand and the smooth muscle relaxes here after opening up tiny sacs in the erectile tissue that then swell with the blood. The two main chambers of the penis these the corpus cavernosum, fill and then organ becomes so engorged that the veins that frequently drain away blood these are pressed shut against the tough outer membrane of the erectile chambers.


The result is erection :

Arteries [left] and veins [Right] penetrate the long, here filled carities by running the length of the penis-the corpora cavernosa and the corpus spongiosum. Erection occurs in which when the relaxed muscles allow the corpora cavernosa to fill with the excess blood that fed by the arteries, while drainage of blood through the veins is blocked