The Erectile Response & Raging Boners

Updated: Mar 31

I often get this question on my discord server: Why PDE5 inhibitors such as Viagra, Cialis, and Levitra DO NOT work for some people despite supplementing nitric oxide donors such as L-citrulline/L-arginine?

This question cannot have a single all-encompassing answer. The erectile mechanisms are numerous and pathways, complex. In order to address your problem, it's crucial that you arm yourself with sufficient knowledge on the matter at hand (your stronger hand).

And this is exactly what this article is about. Let's dive in!

Disclaimer: The [Simply Explained] series of articles are simplified for the layman and may contain crude humor and casual language.

"Phallic statues were rampant in ancient times due to fertility worship. Dicks were all the rage back then."

Table of contents:

1. Brief Overview of Penile Anatomy

2. Brief Overview of Penile Neuroanatomy

3. Central Control of Erectile Function

4. My Answer to the Question

5. Final Remarks

1. Brief Overview of Penile Anatomy

"But ... where is the bone?"

This is an article for the layman so I'll keep it simple and get to the point.

The bare essentials you need to know about penile anatomy: the internal pudendal artery, the corpora cavernosa (CC), its smooth muscles and artery, and finally, the neuroanatomy of erectile function.

A: The internal pudendal artery:

"There is no bone"

When blood rushes into your penis, you get an erection which depends on the sum of in-flow resistance from the feeder vasculatures of the penis versus the venous outflow. This artery is the most important since it contributes 70% of the total vascular resistance [1].

As the in-flow resistance is ramped up, the cavernosal sinusoids become engorged, leading to penile lengthening and tumescence.

Under normal circumstances, erections are maintained because the engorging sinusoids compress the exiting venules and veins, leading to passive limitation of venous outflow [2].

"Disclaimer: Scale model ratio may differ from the product received intrauterinally"

The internal pudendal artery gives off several branches. The most important branch for erectile function is, perhaps, the artery to the corpus cavernosum (aka deep penile cavernosal artery) [3].

B: The corpora cavernosa (CC):

The two CC function as vascular 'tanks' that are blood-filled during an erection, giving girth and structure to the erected penis.

"aka Spongebob's long-lost brother"

It gets its blood supply mainly from the aforementioned deep penile cavernosal artery. It's important to note that the glans of the penis gets its blood supply from the deep dorsal artery instead, which is another branch of the internal pudendal artery [4].

C- The cavernous smooth muscles (CSM) are critical for the physiological role of the CC as vascular tanks or capacitors. The CSM control the vascular events leading to an erection and constitute approximately 40-50% of tissue cross-sectional area [1] [5].

As human males age, they keep losing those smooth muscles due to apoptosis (programmed cell death). Apoptosis and autophagy are modulated by androgens. As such, androgen deprivation, or reduction due to aging, leads to structural changes of the CC [6].

2. Brief Overview of Penile Neuroanatomy

I know that neuroanatomy can get boring fast. But you are so sick of PSSD that you are gonna read it anyway, right? right? I have faith in you!

A- Autonomic Pathways:

These are divided into sympathetic and parasympathetic innervation of the penis. The pathways start at the level of spinal segments, making it in part a reflex process.

- Sympathetic: originates from the 11th thoracic to the 2nd lumbar spinal

"Corona lockdown? watch Jurassic Park"

segments. Stimulation of this thoracolumbar sympathetic pathway is triggers detumescence (no erection).

- Parasympathetic: originates from the 2nd sacral to 4th sacral spinal segments. Stimulation of this sacral parasympathetic pathway triggers tumescence (yes erection).

This means that the sacral parasympathetic input is responsible for tumescence and the thoracolumbar sympathetic pathway is responsible for detumescence [5].


Remember when I said this is in part a reflex process?

This is called a reflexogenic erection: an erection that occurs solely due to direct penile stimulation or when you have a full bladder. The brain has no control over this. It's purely a spinal reflex [7].

There are two other types of erections, one called a psychogenic erection: an erection that occurs only when you think lewd thoughts or from lewd audiovisual stimuli [7].

The other is the nocturnal erection: an erection that occurs mostly during REM sleep, which is triggered within the pontine reticular formation (pons of the brainstem) [7].

In spinal cord injury, many patients with sacral spinal cord injury retain psychogenic erectile ability but NOT reflexogenic erections. Psychogenic erec