2 MEN’S HEALTH Chapter One Get Back that Lovin’ Feeling Erectile dysfunction—two little words that can make even the most macho man’s knees go weak. After all, the inability to attain or sustain an erection is a frustrating, often embarrassing condition that can affect your relationships and your self-esteem. The good news is that 95 percent of all ED cases are treatable. But to really grasp the causes of ED, it’s important to first understand what happens when things go right. Anatomy of an Erection If you think of an erection as a hydraulic event, you’re right—but the mechanics of your penis are only half the equation. An erection is the result of a delicate but perfectly balanced process that involves the brain, blood vessels, nerves, and hormones. If just one of those elements isn’t functioning, ED can be the result. To simplify this intricate process, let’s compare your erection to a rocket launch. Here’s how it works: think of your brain as the mission control center for erections. Once mission control receives data in the form of arousal, it sends tiny messengers called neurotransmitters to the launch pad, better known as the penile nerves. This reflex action is helped along by the release of testosterone. After your penile nerves have been aroused, they send other messengers to the solid rocket boosters—two cylinders that sit side-by-side inside the penis known as the corpora cavernosa. The main neurotransmitter sent to the corpora cavernosa is nitric oxide (NO), a blood vessel dilator, that allows the blood vessels to enlarge and leads to increased blood flow and swelling of erectile tissue. As the penile tissue relaxes and penile arteries expand, the blood flow into the erection chambers increases and the penis grows in width and length. The veins that would normally drain the blood flow are compressed against the inner wall of the tunica albuginea, a dense, elastic, fibrous envelope that covers the corpora cavernosa. By trapping this excess blood, your penis becomes hard and erect. In other words, Houston, we have lift off!