Understanding the science of erection

An erect penis is the primary requisite for any sexual act. It is the phase when the penis is stiff and erect, and aids proper penetration into the vagina.

The human penis is a wondrous contraption. Understanding how it changes from flaccid to stiff, and flaccid again, can be an amazing experience!
The process of erection starts with the brain. The various sexual stimulations prior to insertion send signals to the brain. The brain receives these signals, processes them, and, in turn, sends out further signals down to the penis.

Acting upon the brain’s signals, the blood vessels in corpus cavernosum, the sponge like tissue of the penis, relax. This causes more blood to fill in. At the same time, the veins that lead out the blood get constricted, and the blood flow out of the penis is stopped. Thus, the end result is a blood-filled penis. This is the reason for it to become elongated, and hard. This completes the process of erection.

The expansion of the penis is limited by a tough membrane called Tunica. This tunica is present around the corpus cavernous.

During erection, the blood flow to the penis increases eight folds. Most of this blood comes from various parts of the body, mainly the head.

At the moment of orgasm, the signals from the brain change rapidly, and the blood flows out of the penis, causing the erection to subside.