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The anatomy of the penis
The penis contains:
- Two chambers called the corpora cavernosa,
which run the length of the organ and contain a maze of blood
vessels shaped like cavernous spaces (like a sponge)
- The urethra, or channel for urine and sperm, which
runs along the underside of the corpora cavernosa
- Erectile tissue, which surrounds the urethra, two main arteries and
several veins and nerves
- The shaft, the longest part of the penis
- The head (glans), which is at the end of the shaft
- The meatus, or opening at the tip of the head
where urine and semen are discharged.
How does an erection occur?
When the blood vessels of the corpora cavernosa relax and open up,
blood rushes in through the cavernosus arteries to fill them. The blood then
gets trapped under high pressure creating an erection.
An erection begins with sensory and mental stimulation. During sexual
arousal, nerve messages begin to stimulate the penis. Impulses from the brain
and local nerves cause the muscles of the corpora cavernosa to relax,
allowing blood to flow in and fill the open spaces. The blood creates pressure
in the corpora cavernosa, making the penis expand and creating an
erection. The tunica albuginea (the membrane surrounding the corpora
cavernosa), helps to trap the blood in the corpora cavernosa, thereby
sustaining erection. Erection is reversed when muscles in the penis contract,
stopping the inflow of blood and opening outflow channels.
How does ejaculation occur?
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