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The Biology Behind an Erection

Apr. 8, 2010
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What is the biology behind an erection? Can men have erections without testicles? Without a prostate?

The short answer to your question is that it is physically possible to have an erection without testicles or a prostate, but the removal of either makes it less likely that erections will occur.

Inside the shaft of the penis are three columns of erectile tissue—the two corpora cavernosa, which run parallel to each other along the top of the penis, and the corpus spongiosum, which runs along the bottom of the penis and surrounds the urethra. Despite the fact that erections are often called “boners,” there are no bones within the penis. During an erection, the corpora cavernosa and the corpus spongiosum, which are rich in blood vessels, become engorged with blood and expand, making the penis larger and firmer. The fancy name for this is “vasocongestion.”

Vasocongestion is not caused by the testicles or the prostate; it’s caused by nerve impulses that are sent to and from the penis at two different locations in the spinal cord. The first, called the sacral erection center, is located at the base of the spine, and it responds to direct physical stimulation of the penis. The second, called the thoracolumbar erection center, is located higher in the spine, and it responds to nerve impulses from the brain—sights, sounds and fantasies that are arousing to a particular individual. So, the nerve impulses that signal the body to get an erection can be caused by physical or by psychological stimuli. Reflexive erections that have nothing to do with stimulation can also occur, as anyone who’s ever had a wet dream or spontaneous hard-on can attest.

In addition to producing sperm, the testicles also produce male hormones, including testosterone. Testosterone has a sizable effect on sexual desire, and, in turn, sexual desire is often the first stage in sexual arousal and erection. If the testicles are removed and testosterone production slows or stops, then sexual desire typically decreases, and erections may be fewer or nonexistent.

The prostate is a gland that surrounds the urethra in men and produces about 30% of the fluid that makes up ejaculate or “cum.” It is also a gland that is particularly prone to cancer, especially as men age, which makes it important to get regular prostate examinations if you have a prostate and are 50 years or older. Treatments for prostate cancer, including surgical removal of the prostate, can cause erectile dysfunction (an inability to get an erection). This is not because the prostate is necessary to have an erection, but most likely because of the nerve or blood vessel damage caused by surgery or radiation treatments, or because of the psychological trauma associated with prostate cancer.

Want Laura to answer your questions in SEXpress? Send them to laura@shepex.com. Not all questions received will be answered in the column, and Laura cannot provide personal answers to questions that do not appear here. Questions sent to this address may be reproduced in this column, both in print and online, and may be edited for clarity and content.

Laura Anne Stuart has a master’s degree in public health and has worked as a sexuality educator for more than a decade. She owns the Tool Shed, an erotic boutique on Milwaukee’s East Side.


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