Erection is such a complex process that it’s a miracle men complain about having problems with it so rarely. If speaking in abstract physical terms, erection is a hydraulic process. Blood flows into the shaft of the penis through arteries, filling the two corpora cavernosa - shafts of spongy tissue. From there, the blood is collected in venules and flows out of the penis in larger veins. An erection takes place when the smooth muscles in the walls of the penis relax. This results in widening of arteries, which brings more blood to the corpora cavernosa. It swells, resulting in pressure that narrows the venules, blocking the blood from flowing out of the erect shaft. During detumescence this process takes a reversed direction: the arteries start to narrow, the blood flow is reduced, the veins widen, which lets the blood to flow out from the penis, returning it to the initial flaccid state.

Since a good blood circulation is the key to a good erection, it’s obvious that having healthy arteries and veins is necessary for proper functioning of the penis. But besides that, the nervous system and hormone levels also affect erection.

The nervous system affects erection in two ways. The brain controls libido or sexual desire as we know it.  When sexual arousal takes place, the nervous impulses are transmitted to the pelvis through the spinal cord, where they transmit information to the nerves of the autonomic nervous system. It is the place where the sensory nerves from the penis skin and other sensitive areas are connected. The autonomic nervous system sends signals to the arteries, which when stimulated relax the smooth muscles of the penis, increasing blood flow inside the penis shaft. Ejaculation is also controlled by the nervous system. The nervous system causes the epididymis muscles, prostate, vas deferens and seminal vesicles to contract, which results in the propelling of semen.