Before a man's sexual arousal begins he is in a relaxed state. His muscle
tension, blood pressure, heart rate and respiratory rate are at levels normal
for him.
During this time, in the penis, the arterial blood vessels are constricted
and the venous blood vessels are uncompressed, giving a balance of blood flow
in and out of the corpora cavernosa.
Excitement Phase.
The excitement phase of a man's sexual response is begun by one or more of at
least two distinct mechanisms, which interact in normal sexual activity. Central
psychogenic erections begin in response to stimulus from the brain; imagination,
memories or pr0n, for the most part. Reflexogenic erections begin in response
to stimulus of the penis. Sensory receptors on the penis receive the stimuli
which, through spinal interactions, cause somatic and parasympathetic
efferent actions.
During the excitement phase, blood flow to the corpora cavernosa increases
dramatically. This increase is due to smooth muscle relaxation in the trabeculae and
arterial vasculature, and causes the cavernosal spaces to fill rapidly.
This rapid filling causes the compression of the venous plexus and the larger veins passing through the
tunica albuginea, effectively cutting off the escape route for the blood
filling the penis. This process is often referred to as the corporeal
veno-occlusive mechanism.
It is the combination of increased inflow and decreased outflow from the corpora
cavernosa which causes the penis to harden into erection.
During the excitement period vasocongestion also makes nipples hard,
tightens the scrotum up, and swells the testes.
The man's heart rate, muscle tension, and blood pressure rise
Depending on the man, and on his desires at the time, this phases can last
from about three minutes to several hours.
Plateau Phase
The erection process described above continues until the penis is fully rigid
and the testes are enlarged to approximately 50% again of their resting size
During this period, Cowper's or Bulbourtheral glands
produce pre-ejaculatory fluid.
Blood pressure, heart rate, respiratory rate, and muscle tension continue to
increase. Many men experience a "sexual flush" - redness of skin
mostly appearing on the chest.
Orgasmic Phase
Just before orgasm, rhythmic contractions of the seminal vesicles, vas
deferens, prostate and ejaculatory ducts push semen into urethra. This is
the time known as the "point of imminence"; a few seconds during
which a man knows he will orgasm no matter what happens.
At orgasm the urethra contracts all along itself, forcing the semen out. The
pelvic floor and anal sphincter contract at the same time. The first few
contractions are strong and less than 1 second apart. Weaker contractions follow
for up to several seconds. Most of the sensation of orgasm is felt in the penis
itself.
It is interesting to note that physical stimulation of genitals not always
needed. Some men can achieve orgasm by thought alone.
Resolution Phase
This phase is basically a return to the relaxed state. Blood drains away from
genitals as the corporeal veno-occlusive mechanism gives up it's hold, allowing
the penis to soften into its resting state. The testes return to their normal
size, the scrotum relaxes, muscle tension decreases, nipples soften and any sex
flush that was apparent begins to disappear.
Heart rate, breathing and blood pressure return to normal.
Refractory Phase
This is where male sexual response differs most from female. The refractory
period is a time during which a man simply cannot have an orgasm no matter what
the stimulus.
In younger men the refractory period is generally a few minutes. In older
men, or those with hormone deficiencies, the refractory period can last hours or
even days.