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wikify shaft skin
== A well-integrated organ ==
Structurally, the penis is highly integrated. The glans, foreskin and [[shaft skin|skin]] of the penile shaft ]] function as a single unit, not as a collection of separate parts with entirely different functions. The functions of the glans and foreskin are similar, and overlapping, but come fully into their own at different times during intercourse.
== Simple sensations ==
== Complex sensations ==
Thanks to its ridged band, the inner lining of the foreskin is specialized sexual tissue. The ridged band readily expands and contracts and is obviously designed to detect stretching forces. When penile shaft [[shaft skin]] tugs on the ridged band, special genital corpuscles in the peaks of the ridges detect movement and trigger ejaculation. Stretching of the ridged band may also trigger and sustain erection.
Electrical stimulation of the glans triggers nerve impulses that pass to the spinal cord and then to the muscle of ejaculation. Clearly the glans has much in common with the foreskin. Where foreskin and glans part company, functionally as well as physically, is in their sensitivity to light touch, pain and heat and cold. Contrary to common opinion, the glans is not highly sensitive to a broad range of stimuli.
== Dartos muscle ==
Penile [[skin]] has two important characteristics, apparent only on erection. Firstly penile [[skin]] tenses, stiffens and shortens, firming up the connection between shaft [[shaft skin]] and ridged band. This change allows for the transmission of movement from the base of the erect penis to the ridged band.
Secondly, penile [[skin]] undergoes a marked frictional change, brought about by stiff, forward-pointing [[skin]] folds. The mechanism is similar to that which raises goosebumps.
== Why two layers? ==
The double-layering of the foreskin allows the delicate ridged band, which normally is safely hidden from view, to be deployed on the upper surface of the penile shaft during erection. There it stands a better chance of being activated. Double-layering also eases vaginal entry by offsetting the frictional resistance of erect shaft [[shaft skin]].
== Summary ==