ERECTION
( how it works )
To
get an erection, blood vessels at the entrance of the penis
open up and allow blood to flow in. The blood (warm,
and therefore red, in the heat-sensitive photo), enters
the sponge-like tissue of the corpus
cavernosum and corpus
spongiosum. As the blood fills into the penis,
an erection forms. Erections are brought about through
the parasympathetic nervous system when the penis, or other
erogenous zones, are touched. In addition, certain
sights, sounds, smells, thoughts and dreams (either day-dreams
or night-time dreams) can trigger the blood vessels to open
and an erection to form. From early childhood onwards,
erections occur during sleep. This phenomenon, called
nocturnal penile tumescence, occurs during REM sleep
(Rapid Eye Movement) and usually occurs for about 100 minutes
a night. Having an erection upon wakening in the morning
is an example of this phenomenon.
With
continuing stimulation, an orgasm can occur. The orgasmic
expulsion of semen from the penis (ejaculation) is a reflex,
much like when the doctor checks your knee reflex.
Whereas an erection can be interrupted at any moment by
will (or from fear), the ejaculation reflex, once started,
cannot be stopped. Once triggered, the reflex begins
with the movement of sperm from the
epididymis (e) (where sperm is stored after being made
in the testicle) to the vas
deferens (vas). The sperm moves into the prostate
(pr), and mixes with secretions from the prostate and
seminal vesicles and is then expelled through the urethra.
In healthy adults, about 3 cc of semen (containing 300 million
sperm) are released with each ejaculation.
