How erection occur

When sexually stimulated, a man's brain sets his system in motion to create an erection. The stimulation can be mental (thinking about something that arouses him), visual (seeing something or someone who turns him on), or physical (having his body or penis touched, for example). People can also be stimulated through their other senses, such as by certain odors or sounds. As a man grows older, he usually needs more direct physical stimulation in order to get an erection.

The erection process involves the hormonal, neurological, vascular, and muscular systems of the body working together. It begins with our most important sexual organ, the brain.

When you are sexually stimulated, whether through mental, visual, and/or physical means, your brain sends messages to several parts of the body, including the nerves, glands, muscles, and vascular system. It works like this:

Nerve impulses move down the spinal cord to the penis penile nerves set off the release of the neurotransmitter, nitric oxide

The nitric oxide causes the small muscles inside the arteries leading to the penis to enlarge in size.

• The penile arteries dilate and allow blood to flow into the penis

• The spongy tissue of the two erectile chambers in the penis fill with blood and become swollen

• The erectile chambers fill up with blood and begin to press against the veins, preventing the blood from leaving the penis

• The tissue continues to fill with blood and expand until the penis is fully erect

At the same time, additional chemical changes are occurring in the body. When nitric oxide is released it sets off the production of several other chemicals, including cyclic GMP (guanosine monophosphate), a smooth muscle relaxant. When the cGMP washes over the penile tissues, they relax and begin to swell. Later, when sexual activity has ended, an enzyme, phosphodiesterase, breaks down the cGMP and the penis goes back to its flaccid state.

This multi step cyclical procedure has taken the penis from its soft or flaccid stage to its swollen or tumescent stage then to its rigid or erect stage, and finally, back to its original flaccid state.