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 a picture of the blood supply to the penis.
Four requirements for a normal erection are:
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Adam Husney, MD - Family Medicine
Specialist Medical Reviewer Christopher G. Wood, MD, FACS - Urology, Oncology
Current as ofMay 24, 2016
To learn more about Healthwise, visit Healthwise.org.
© 1995-2016 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.
Donations to UW Health are managed by the University of Wisconsin Foundation, a publicly supported charitable organization under 501(c)(3) of the Internal Revenue Code.