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Normally, an erection occurs when your
imagination or one or more senses (vision, hearing,
touch, smell, taste) are stimulated and you become
aroused. Your central nervous system sends nerve
impulses that increase blood flow to your penis. Four
requirements for a normal erection are:
-
A properly functioning nervous system
that sends the necessary signals to the penis.
-
An intact system of blood vessels to
allow blood to flow into and out of the penis.
-
Normal smooth muscle in the penis, which
must relax so the penis can fill with blood and enlarge.
-
The ability to trap the blood in the
penis so that it stays firm.
Erectile dysfunction can occur at any
age but is more common in older men, who often have
additional health problems or who may be taking
medications that may interfere with normal erectile
function. Treatment of erection problems in older men
can be as effective as in younger men.
Doctors prefer to use the term erectile
dysfunction instead of impotence. A man's sexual
function involves more than an erection, and the term
impotence often carries negative implications. For ease
of reading, this topic uses the term erection problems
to refer to erectile dysfunction.
Erection problems can affect your sexual
life and your relationship. Discussing the issue with
your partner and exploring other forms of intimacy can
help improve your relationship and the erection
problem.
The
anatomy of the penis
 
Corpora cavernosa:
two cylindrical tissues run
the length of either side of the penis. Like
sponges, they are capable of filling with blood.
When the penis is soft, the muscle fibres in the
corpora are contracted.
Tunica:
a tough outer sheath that
surrounds the corpora and limits the amount they
can expand. As the tunica becomes tight, blood
flowing into the penis raises the pressure
within it, making it hard.
Corpus spongeosum:
a third cylinder of tissue
between the two corpora. This contains the
urethra, through which urine and semen pass out
of the body. It thickens towards the tip of the
penis to form the helmet-shaped glans, which is
covered by foreskin in uncircumcised men.
How an erection
happens
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1.
Touch, sights, sounds,
erotic memories, fantasies etc, cause sexual
excitement.
2.
These stimuli increase
signal output from a part of the brain called
the para-ventricular nucleus.
3.
These signals then pass
through special autonomic nerves in the spinal
cord, the pelvic nerves and the cavernous nerves
that run along the prostate gland to reach the
corpora cavernosa and the arteries that supply
them with blood.
4.
In response to these
signals, the muscle fibres in the corpora relax,
allowing blood to fill the spaces between them.
5.
Muscle fibres in the
arteries that supply the penis also relax, and
there is an eight-fold increase in blood flow to
the penis. The increased blood flow expands the
corpora, then stretches the surrounding sheath
(the tunica).
6.
As the tunica stretches, it
blocks off the veins that take blood away from
the corpora cavernosa. This traps blood within
the penis, the pressure becomes very high and
the penis becomes erect.
7.
During an erection pressure
in the penis is at least twice the pressure of
blood in the main circulation. This is possible
because the muscles of the pelvic floor contract
around the base of the corpora cavernosa.
8.
At orgasm, the signalling
from the brain changes dramatically. There is a
sudden increase in noradrenaline production from
nerves in the genitalia. This seems to both
trigger orgasm and contract the muscle fibres in
the corpora cavernosa and their supplying
arteries.
9.
The pressure within the
corpora drops, which also relaxes the tunica and
so allows blood to flow out of the penis.
What causes erection problems?
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