Cause of an erection

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Cause of an erection

An erection occurs when your imagination or one or more of the senses (vision, hearing, touch, smell, taste) are stimulated and you become aroused. Your central nervous system sends nerve impulses that increase blood flow to your penis. The blood fills the spongy chambers (corpora cavernosa) in the penis, causing them to expand and become rigid. The veins that would normally drain blood from the penis are constricted, trapping the blood inside and maintaining the erection.

An erection goes down because the arteries narrow, the veins expand, and the blood drains out of the penis. The penis returns to its normal size and is no longer rigid.

See an illustration of the blood supply to the penis .

Four requirements for a normal erection are:

A properly functioning nervous system that sends the necessary signals to the penis.
An intact system of blood vessels (vascular system) to allow blood to flow into and out of the penis.
Normal smooth muscle in the penis, which must relax so the penis can fill with blood and enlarge.
The ability to trap the blood in the penis so that it stays firm.

Credits

Author	Ralph Poore
Editor	Kathleen M. Ariss, MS
Associate Editor	Pat Truman
Associate Editor	Terrina Vail
Primary Medical Reviewer	Adam Husney, MD - Family Medicine
Primary Medical Reviewer	E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer	Christopher G. Wood, MD, FACS - Urology/Oncology
Last Updated	June 13, 2006

Last updated:	June 13, 2006
Author:	Ralph Poore
Reviewed By:	E. Gregory Thompson, MD - Internal Medicine, Christopher G. Wood, MD, FACS - Urology/Oncology
Editors:	Kathleen M. Ariss, MS, Terrina Vail

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