NEWSLETTER

August 2008

At least one noted physiologist claims that erogenous touch is the main trigger of sexual reflexes for ejaculation. This seems to be the general opinion. Erogenous sensation is also the result rather than the cause of sexual reflexes so does it really matter which comes first, sensation or reflexes?

What we have shown over the past several years is that the prepuce or foreskin is specialized to trigger sexual reflexes for orgasm and ejaculation. The ridged band of prepuce is a major trigger of this reflex. It is not the only trigger; the glans also plays a role even if it is not the role commonly supposed.

Reflex contraction of bulb muscles around the bulb of the penis, perhaps due to stimulation of the glans or foreskin, is essential for ejaculation. Voluntary or willed contraction of bulb muscles clears residual urine from the posterior urethra. The glans usually survives circumcision intact: the foreskin is less fortunate and, hence, top priority for our attentions. Still, keep in mind that both glans and foreskin contribute to a single mucosal-skin junction of the penis and it is not possible to separate them physiologically. They may look different but they have much in common.

Glans and ridged band also share the same neural reflex arc. Specialized nerve endings (large, onion-like Meissner corpuscles) of the penis send nervous impulses through the main sensory nerve of the penis to the spinal cord. Nerve impulses exit the spinal cord in nerves to the prostate, seminal vesicles and bulb muscles at the base of the penis. This is how stretching of the ridged band triggers rapid, reflex contraction of the prostate etc. If repeated often enough we have orgasm and ejaculation. Deep - as distinct from superficial - erogenous sensation felt in the pelvis is an important consequence of reflex pelvic organ contraction.

We have seen that the foreskin is a major trigger of sexual reflexes leading - if thrusting continues in response to deep erogenous sensation - to orgasm and ejaculation. Now we have to know how the foreskin and its ridged band cooperate with shaft skin during intercourse.

What about the foreskin and muscularized skin of the penile shaft and scrotum? During erection, skin of the penile shaft and scrotum undergo contraction, shortening and stiffening. Such changes are very obvious in loose scrotal skin, particularly at its junction with the penis. In addition, shaft skin on the upper surface of the penis, usually the main sexual contact surface of the intact penis, develops stiff, forward-pointing skin folds. These skin changes are sufficient to enhance the frictional capacity of the erect penis. Scrotal skin extending 2-4cm onto the base of the penile shaft ('pars scrotalis', the hairy part), further tenses shaft skin, thereby enhancing its ability to transmit thrusting movement to a the retracted prepuce and ridged band, held relatively immobile against the vagina by the skin folds. In short, the muscular skin of penis and scrotum helps activate, 'at-a-distance', a train of sexual reflexes during thrusting to ejaculation. The reproductive advantage of this is clear although I have to admit the idea of 'frictional' penile skin will disturb traditionalists.

The next problem is the function of corpus spongiosum, the spongy vascular body surrounding and unique to the male urethra and which becomes engorged with blood during erection. The posterior end of corpus spongiosum, just behind the scrotum, is bulb-like; this bulb of the corpus spongiosum is compressed by both reflex and voluntary contraction of bulb muscle. (At present, the purpose of bulb muscle contraction is thought to be compression of the posterior urethra, in the middle of the bulb; if anything, corpus spongiosum is thought to enhance urethral compression during ejaculation). We say on the contrary that bulb muscle contraction is designed to send pressure waves, along corpus spongiosum, to the glans, essentially its anterior bulb. Thus compression of one end of this dumb-bell shaped structure causes expansion of the other. I do not know if this mechanism is restricted to males; females also have a system of vessels, around the urethra, connected to glans of clitoris, so anything is possible. To sum up, the corpus spongiosum is a simple, fail-proof hydraulic mechanism for iteration of sexual reflexes. In support of this theory, the wide-radius corona of glans is structured to respond to 'bulb wave' pressures, as explained by the physical Law of LaPlace relating wall tension -hence wall stretchiness - to vessel diameter. The more the coronal surface expands, the more its Meissner corpuscles are stretch, and the more they send out signal for bulb muscle contraction etc.

In practice, the corona of glans does expand momentarily in response to the 'bulb wave', triggering a secondary or 'echo' reflex for further bulb muscle contraction. Our questionnaire addresses the bulb wave hypothesis. If nothing else, we may be able to give corpus spongiosum a sexual function equal to its size and connections; it is almost certainly more than simple support for the urethra, which has plenty of alternative support throughout its length.

The role of a secondary or 'echo' reflex in so-called voluntary bulb muscle contraction at the end of urination, or simply for practising our tests, is also worthy of consideration. The conscious act of expressing urine from the posterior urethra may be rather more complex, and vigorous, than we think it is. Some felines have developed this knack to a fine art.

The glans has garnered a great deal of attention, much of it intuitive. And intuition is always a problem in science. All too often things, like the prepuce, are not what they seem to be at first sight. Firstly, and contrary to popular imagination, the glans is relatively insensitive to light touch and the intact penis fares no better that the circumcised penis in this regard. So, what does the glans do? Well, it is shaped to expand. Coronal expansion stretches Meissner corpuscles embedded in the surface mucosa of the corona like currants in a bun; these in turn trigger reflex bulb muscle contraction. Thus, the glans is almost certainly part of a system for repetition of sexual reflexes and erogenous sensation. In other words, glans and ridged band reflex functions are very similar, in keeping with the demands of parsimonious Nature.

To put this another way, triggering, say, the ridged band reflex sets off a chain of events in the penis, one contraction of bulb muscles multiplying into four or more contractions without further input from ridged band stretching. This does not take into account the effect of retraction of the frenulum on the tip of the glans, sharp flexion of which across the pulley-like tips of the erect corpora cavernosa, the main erectile bodies of the penis, is readily transmitted to coronal receptors, with induction of yet another set of sexual reflexes. The frenulum is another structure looking for a sexual function. I believe it is little more than a flexor tendon although others may think differently.

What my colleagues and I stress is that the foreskin is an extremely important sensory structure that mediates sexual reflexes. This is not rocket science requiring elaborate equipment. All it requires are open minds and a willingness to explore new ideas.

Finally, the child`s large foreskin is an adult structure for adult use; in fact, at birth it is probably the most advanced part of the human sexual apparatus. Unlike other tissues with roles in the propagation of our species, the foreskin changes very little between birth and puberty.

Thank you for taking time to read this newsletter. I hope it is useful.

John R Taylor