Penile Erection 

Physiology of Erection - How the Penis Works


The creation of an erection is an extremely complicated cascade of events that requires many different things to happen. There are numerous chemical transmitters involved in this including epinephrine, norepinephrine, acetylcholine, prostaglandins and nitric oxide. The exact mechanism by which erection occurs is still unclear but we do know that the neural input from the brain is extremely important. Reflex erections, as seen in people with cord damage such as paraplegics, are often poor erections and not sustainable for prolonged periods of intercourse.

An erection occurs when the nervous system activates a rapid increase in blood flow. The vascular muscle in the spongy area becomes engorged with blood and the outflow of blood is cut off. An erection can occur as a reflex as we see in spinal cord patients, or can be caused by psychogenic (originating in the mind) stimulation. Numerous sexual stimuli are processed by the brain and transmitted to the penis via the nervous system. 

In order to increase the size of an erection, there must be an increase in blood flow and, at the same time, the blood has to be prevented from leaving the penis. Blood flows to the penis by two very small arteries that come from the Aorta. These arteries are the same size as the arteries to your finger. The main problem that causes impotence is that the blood vessels become blocked and the blood can not get to the penis. The other major problem is leakage of blood from the penis into the veins around the penis called a venous leak. This is very common, similar to a hole in a tire. The larger the hole the more air that needs to be pumped into the tire to keep it hard!