In an aroused male, a series of events leads to the relaxation of the smooth muscle and the entrapment of blood in the expandable sacs. The events begin with sexual stimulation, which triggers the autonomic nervous system to release neurotransmitters. In the penis, the cavernous nerves release neurotransmitter into the endothelial cells of the arteries. NO relaxes the smooth muscles of the corpus cavernosum through a cascade of biochemical reactions to be discussed later. The blood is trapped in the corpus cavernosum and the penis becomes erect.
Impotence can be the result of interference or problems at any one of the above stages.
A problem can occur at the psychological level, impeding the necessary sexual stimulation needed for penile erection. It can also occur at any of the biochemical steps at the cellular level. With the discovery of the role of NO in penile erection, the source of the impotence problem became clearer and new treatments could be discovered. Nitric oxide displays unique chemistry due to its paramagnetic, radical nature. Now, NO is known to be involved in a myriad of biochemical processes in the human body, including smooth muscle relaxation.