Failure to achieve erection results when the penis does not fill or empty appropriately. The penis has two chambers called the corpora cavernosa. These chambers run the length of the penis and are filled with a spongy tissue which contains smooth muscles, fibrous tissues, spaces, veins and arteries. The corpora cavernosa are surrounded by a membrane called the tunica albuginea. The urethra, which is the pathway for both urine and semen, runs along the underside of the corpora cavernosa.
Erection begins when a man receives sensory and mental stimulation.
Impulses from the brain and nerves around the penis cause the muscles of the corpora cavernosa to relax, allowing blood to flow in and fill the open spaces. This blood creates pressure in the corpora cavernosa, which makes the penis expand. By helping to trap the blood in the corpora cavernosa, the tunica albuginea sustains the erection. Erection is reversed when the muscles in the penis contract, stopping the blood from flowing in and opening the channels that allow the blood to flow out. For more information about impotence, select from the list below.