The Fickle Phallus

Andrew Siegel MD  6/10/17

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The penis is a fickle and temperamental friend who can be volatile, unpredictable and even hot-headed at times.  He has many states of existence, ranging from as shrunken and soft as a marshmallow to a “proud soldier”– rock-hard with exquisite posture. Between deflated and inflated, there are an infinite number of intermediate states, dependent on the dynamic balance between the closing and opening mechanisms of the blood flow to the penile erectile chambers.  It is important to understand that the same physiology applies to female genitals and clitoral function. 

The Autonomic Nervous System: The Network Ultimately Responsible for this

The autonomic nervous system controls “unconscious” body functions, including heart rate, breathing, digestion and contributes in a large way to regulate sexual function.

Heart rate and contraction are dynamic, changing moment-to-moment, even beat-to-beat, since they are “governed” by two competing halves of the autonomic nervous system.  The two systems—sympathetic and parasympathetic—are in a constant tug-of-war based upon external stimuli and one’s interpretation of them.

The sympathetic nerves respond to threats, fears and anxieties —an agitated state of mind and blood vessel tone—with the classic flight-or-fight response, which accelerates heart rate, heart contractility, respiratory rate, blood pressure and constricts arteries throughout the body.  The sympathetic system boots up when one is presented with a sudden anxiety-provoking event, such as being in a near-miss car accident.

On the other hand, the other half of the autonomic nervous system is the parasympathetic nervous system—the calmer and more relaxed state of mind and blood vessel tone—which slows down heart rate and respiratory rate, reduces heart contractility and lowers blood pressure by dilating arteries. The parasympathetic system is the system that predominates when we are not in situations that provoke fear and anxiety, governing many day-to-day bodily functions.


Above image from Wikipedia, in public domain


Erectile function is complex and based upon many factors, both physical and psychological, but the ultimate determinant is chemistry that drives penile blood flow or lack thereof.  The state of the penis (flaccid vs. rigid vs. any intermediate state) at any given moment is based upon the balance between sympathetic (contractile) and parasympathetic (relaxant) factors. As the cardio-vascular system function is predicated upon the predominance of sympathetic versus parasympathetic stimulation, so the function of the peno-vascular system is predicated upon the predominance of sympathetic versus parasympathetic function. After all, the penis can be considered to be an extension of the vascular system that can be referred to as the “dangling aorta.”

Penile erection occurs with activation of parasympathetic (nitric oxide-cyclic guanosine phosphate pathway) nerves, which foster the relaxation of the penile arterial smooth muscle and the smooth muscle of the erectile tissue and inhibition of contractile mechanisms, all of which cause blood to rush into and inflate the penile erectile chambers.

Alternatively, penile flaccidity occurs with activation of sympathetic (norepinephrine pathway) nerves, which foster the contraction of the penile arterial smooth muscle and the smooth muscle of the erectile tissue and inhibition of relaxing mechanisms, all of which causes blood to exit and deflate the penile erectile chambers.

Sympathetic nervous system activity causing increased smooth muscle tone in erectile tissue is likely involved in the occurrence of psychological as well as in cardiovascular erectile dysfunction.

The bottom line is that the state of penile inflation at any given moment is highly influenced by the balance between sympathetic and parasympathetic function. High sympathetic activity causes a shriveled and decompressed penis, while high parasympathetic activity an erect and rigid penis. This is the very reason why one needs to have a relaxed temperament in order to perform sexually and also explains why anxiety can doom erectile function. A perfectly healthy 21-year-old with absolutely normal “plumbing” can be doomed to sexual failure if performance anxiety creates such a high sympathetic tone state. Similarly, a 50-year-old man who uses Viagra to increase penile blood flow and help obtain a rigid erection can have the beneficial effect of the medicine neutralized by a highly anxious state of mind.

Wishing you the best of health,

2014-04-23 20:16:29

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Dr. Andrew Siegel is a practicing physician and urological surgeon board-certified in urology as well as in female pelvic medicine and reconstructive surgery.  Dr. Siegel serves as Assistant Clinical Professor of Surgery at the Rutgers-New Jersey Medical School and is a Castle Connolly Top Doctor New York Metro Area, Inside Jersey Top Doctor and Inside Jersey Top Doctor for Women’s Health. His mission is to “bridge the gap” between the public and the medical community that is in such dire need of bridging.

Author of MALE PELVIC FITNESS: Optimizing Sexual & Urinary Health

Author of THE KEGEL FIX: Recharging Female Pelvic, Sexual and Urinary Health

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2 Responses to “The Fickle Phallus”

  1. Joe Gass Says:

    Not a comment but a question……….: How does sleep apnea affect sexual function?

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