Changes

The foreskin and the glans have similar functions. Both are designed to trigger nerve impulses that lead to erection and ejaculation. The glans detects deep pressure and movement. The foreskin detects movement through the accordion-like action of the ridged band; in addition, the outer, true [[skin ]] of the foreskin has an exquisite ability to detect light touch and pin-prick. The glans lacks these abilities because it relies on the covering foreskin to provide them.

The ridged band is part of a muco-cutaneous junctional zone, so called because it lies at the junction between true [[skin ]] and mucous membrane. Like all such zones, it is equipped with special sensory nerves designed to detect movement. Some junctional zones, such as the lips and eyelids, detect movement through bristle-like hairs. For obvious reasons, the foreskin lacks bristles; instead it is deeply ridged. Its ridges open and close, accordion-like, when the foreskin is stretched. This movement probably helps stimulate motion-sensitive nerve endings in the ridges. Thus the foreskin, lips and eyelids are variants of a basic structural design that differs according to location and type of mechanical stimuli encountered.

The ridged band, which is mucous membrane ([[mucosa]]), is joined directly to the true [[skin ]] of the penis. The glans, on the other hand, does not come in direct contact with true [[skin]]. This arrangement suggests that the ridged band depends for stimulation on the tugging action of penile [[skin ]] during intercourse. The glans is more independent of penile [[skin]], both functionally and physically.

The double-layered design of the foreskin does indeed permit smooth penetration and a sliding action. The [[skin ]] of the penis, including the foreskin, becomes rougher during erection. This roughness is brought about by a mechanism similar to that which raises goosebumps. The extra frictional resistance brought about in this way reduces slippage of penile [[skin ]] against female tissues. The double-layering of the foreskin is designed to offset the frictional effect of erect penile [[skin ]] and allow for easy vaginal penetration.