Erection Process

For something that appears so natural, an erection is a rather complicated process involving the coordination of the psychological, neurological and cardiovascular systems.  The penis becomes erect following a series of events.  First, the nerves are stimulated, a sensation known as arousal.  No matter what the nature of the stimulus, visual, mental or physical the brain coordinates the following series of events:

 Nerve impulses transverse the length of the spinal cord to the pudendal nerve and on to the penis.  Smooth muscle within the walls of the penile arteries respond by relaxing.

Subsequently, the penile arteries dilate allowing up to eight times more blood to flow into the corpora cavernosum, (two parallel cylinders that transverse the length of the penis).

The cavernosum become engorged with blood expanding and lengthening the penis.

The expanding tissue then exerts a positive pressure compressing the veins that normally empty the blood from the penis, maintaining the blood in the penile tissue.

When ejaculation occurs or when arousal is discontinued the penis returns to its non-erect state.