More men have been seeking help and returning to near-normal sexual activity because of improved, successful treatments for impotence. A spongy tissue fills the chambers. The corpora cavernosa are surrounded by a membrane, called the tunica albuginea . The spongy tissue contains smooth muscles, fibrous tissues, spaces, veins, and arteries. The urethra, which is the channel for urine and ejaculate, runs along the underside of the corpora cavernosa .
Erection begins with sensory and mental stimulation.
Impulses from the brain and local nerves cause the muscles of the corpora cavernosa to relax, allowing blood to flow in and fill the open spaces. The blood creates pressure in the corpora cavernosa , making the penis expand. The tunica albuginea helps to trap the blood in the corpora cavernosa , thereby sustaining erection. Erection is reversed when muscles in the penis contract, stopping the inflow of blood and opening outflow channels. Since an erection requires a sequence of events, impotence can occur when any of the events is disrupted.