From the Guidelines
The penis does not contain skeletal muscle tissue, but rather smooth muscle tissue that plays a crucial role in erection. The penis is primarily composed of three cylindrical chambers of erectile tissue: two corpora cavernosa and one corpus spongiosum, which contain smooth muscle tissue and blood vessels that allow for erection when blood flow increases to the area 1. During sexual arousal, these smooth muscles relax, allowing blood to fill the erectile tissues, which causes the penis to become rigid. Some key points to consider include:
- The absence of skeletal muscle in the penis means that men cannot voluntarily control their erections through muscle contraction, unlike other body parts that contain skeletal muscles.
- Erections are primarily controlled by the autonomic nervous system in response to physical or psychological stimulation rather than conscious control.
- The smooth muscle tissue in the penis functions involuntarily, similar to the smooth muscle found in blood vessels and internal organs throughout the body, as noted in a study on management strategies for erectile dysfunction 1. Key factors that influence erectile function include:
- Corporal smooth muscle relaxation mediated by parasympathetic neurotransmission
- Nitric oxide
- Electrophysiologic events
- Other regulatory factors, all of which contribute to normal penile erection as a hemodynamic process 1.
From the Research
Penis Structure and Muscles
- The penis contains two chambers, the corpus cavernosa, which have sinusoids that fill with blood and expand to become rigid when smooth muscle is relaxed 2.
- The corpus cavernosum smooth muscle and extracellular matrix are essential for normal penile erection and are implicated in erectile dysfunction 3.
- Smooth muscle cells are restricted to the subendothelial space of corpus cavernosum and have a volumetric density of 9.1% in rats 3.
Role of Smooth Muscle in Erection
- Penile erection is a vascular phenomenon that results from smooth muscle relaxation, arterial dilation, and venous restriction 4.
- The relaxation of smooth muscle cells allows blood to flow into the penis, causing an erection 2.
- The key biochemical event in erectile function is an increase in levels of cyclic guanosine monophosphate, which causes smooth-muscle relaxation and allows an erection to occur 2.
Importance of Smooth Muscle Tone
- The intrinsic biological complexity of penile erection and the multifaceted nature of erectile dysfunction are just beginning to be fully appreciated, with a primary role of the corporal smooth muscle 5.
- The importance of corporal smooth muscle tone in the control of erection is crucial, as changes in smooth muscle tone can affect erectile function 5.
- A reduction of smooth muscle cells has been demonstrated in relation to changes in oxygen tension, which can contribute to erectile dysfunction 4.