How does an erection work and why do they happen spontaneously
sometimes
Erection is the scientific term for that state of the penis when
the two corpora cavernosa (two tubular muscles) are filled with
blood. This means that the penis hardens and grows in length to
accommodate the extra blood.
Penile erection is usually the result of sexual stimulation, but
is also known to occur spontaneously, most commonly at night,
during erotic dreams. Erection in males can be caused by
mechanical stimulation, or by the pressure of the bladder, when
full. The exact cause of spontaneous erections is not known. The
erection is crucial to sexual intercourse and most other sexual
activities for males.
>From the physiological point of view, erection is caused by an
increased flow of blood to the penis and by a strong decrease in
the outflow. Muscles around the penis relax in order to allow
the blood into the corpora cavernosa and corpus spongiosum,
while contraction of other muscles reduces the outflow. As the
tubular structures fill with blood, the penis expands in both
length and girth. It also stiffens and rises to a certain angle
(which varies from one man to another).
The sympathetic nervous system is responsible for the failure to
achieve erection under conditions of stress. This system
interferes with the signals sent by the parasympathetic nervous
system, which is actually responsible for activating the
erections.
The inability to achieve or maintain erection is known as
impotence, or erectile dysfunction.
A less known fact is that erections can occur even after death,
due to increased pressure in the penis from sinking fluids or
the accumulation of gases.