How Does Erection Occur?

The mechanism of erection to be discussed here assumes that normal masculine development has occurred at puberty by the correct balance between genes and hormones.

1-The Nervous System

The brain exerts the main control over sexual behavior. Special chemicals (neurotransmitters) are present in the brain, some stimulatory for sexual behavior and some inhibitory. At base line, the brain is under inhibitory effect by day and stimulatory effect at sleep.

Sexual stimulation may be sensory, by touch, visual, auditory, olfactory or imaginary (fantasies). Sensory stimuli (touch) reach the brain from the penis and skin through nerves then up the spinal cord. All of those stimuli converge on the brain to induce the release of more stimulatory neurotransmitters.

The released neurotransmitters fire impulses down the spinal cord, then across the peripheral nerves to the penis.

2-The Penis

Nerve impulses reach the penis via the "pudendal" nerve. The impulses induce neurotransmitters in the penis that start the cascade of events that cause erection.  Nitric oxide (NO) is the neurotransmitter that is most important for erection.

 Nitric oxide (NO) induces dilatation (opening up) of arteries that pump blood at high speed and large volumes into the sinusoidal spaces of the penis. "NO" also induces those spaces to dilate by relaxing the sinusoidal muscles that surround them, thus accommodating the pumped blood inside the corpora cavernosa which are the two longitudinal cylinders spanning the length of the penis and responsible for erection . The penis expands due to the large volume of blood being pumped in. The veins become compressed  against the inner wall of the corpora cavernosa. Being the outlet of blood, the compressed veins prevent blood from leaving the penis. Gradually, blood volume and pressure increase inside the corpora cavernosa leading to rigidity of the penis. Rigidity becomes maximum when a muscle surrounding the base of the penis (bulbocavernosus) contracts, tightening the blood filled penis and increasing blood pressure within.

Nitric oxide (NO) is broken down and degraded by and enzyme named "phosphodiesterase inhibitor" or (PDE)

 

 

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