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The erectile mechanism of the penis

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Perhaps the most widespread and emotive issue for sexual partners is rapid ejaculation, commonly diagnosed if a man achieves orgasm sooner than two minutes after penetration. Since over 50% of men come too soon, it's hardly surprising that most of the time spouses just cannot express their feelings around premature ejaculation. Fortunately, this attitude around this very widespread sexual difficulty can easily be dealt with if a man who lacks ejaculation control really wants to have greater ejaculation control. You can find a lot of self-help systems which explain how to stop early orgasm and last longer in bed. Help is at hand on the net, with information websites containing many tips about how to slow down and end premature ejaculation quickly.

During many years' experience as a sex therapist, I've learned that when a man with PE trains himself to become sexually aroused more slowly, he will soon find it easy to really pleasure both himself and his partner during sex. Some men who do not know how to stop premature ejaculation develop low self-esteem. Definitely, many men feel embarrassment around premature ejaculation, most likely due to worry around satisfying a woman.In some cases this is due to the fact their lovers are frequently left hanging, unsatisfied, after short intercourse.

Are you wondering what lovers actually say about early ejaculation? Scientific studies show sixty five percent of women claimed that PE doesn't worry them - so long as their lover took them to orgasm with cunnilingus or masturbation. Nonetheless, loss of ejaculatory control can still be quite emotional for each of the partners. Husbands seem to think that ejaculating too quickly is, shall we say, pathetic.

Effective premature ejaculation cures can be a relationship-saver. Always try to find the most respected systems. If you purchase a self-help PE program it must be a system which which is stand-alone to adapt for your own requirements. Practice PC muscle control well before lovemaking starts, so you're prepared. The method that you use should be practical, even if passionate male desire makes you to lose awareness. Also, a self-help system must include information for both partners.

Understanding normal erectile function requires a review of the anatomy of the penis.

Summary of Normal Male Erectile Function

A normal erection is the result of a rather complex process. The penis has three separate tubes that become engorged with arterial blood during arousal. Erotic fantasies or sensory inputs such as the touch, scent, sound or sight of a partner are channeled into the control center in the brain. The aroused brain sends signals down the spinal column to the penile nerves (which may also be stimulated directly by manual stimulation - masturbation, fellatio, or intercourse). The nerve impulses trigger an event involving muscle tissue and blood vessels in the two large erectile cylinders, the corpora cavernosa (singular: corpus cavernosa).

There are arteries and spaces called sinusoids within these cylinders, and smooth muscle tissue surrounds the arteries and spaces. Normally, the smooth muscle tissue keeps both arteries and spaces constricted, but the nerve impulses send a primary messenger called nitric oxide (NO). This molecule tells the smooth muscle tissue to relax, which allows more arterial blood to flow into the penis and the capacity of the penis to dramatically increase in volume. Meanwhile, veins that normally drain blood from the penis are flattened by the expanding volume of blood into the erection chambers. The arterial blood is thus trapped, making the penis very hard and very erect. Continued stimulation keeps the process going and maintains the erection.

Now, here is a more complex description:

Anatomy of the Penis

The penis is composed of three erectile cylinders. A pair of spongy cylinders (the corpora cavernosa) are located side-by-side on top. They join in the midline for about 70 pecent of their length - that part of the penis that extends from the body - and continue separately behind the pubic bone where they are anchored to the underside of the pelvic bony structure, the ischiopubic ramus. Thus, about 30 percent of the penis is buried in the pelvis behind the pubic bone. This bony anchor is very important for normal penile function. Where the corpora cavernosa merge at about the level of the pubic bone, the midline surface between the two cylinders forms an incomplete septum. This is important in that it allows blood to pass freely from one corporal body to another.

A single corpus spongiosum is located below the junction of the two corpora cavernosa. This simple tube encloses the urethra and at its tip forms the glans penis, commonly referred to as the "head" of the penis. The urethra extends from the bladder to the tip of the glans penis.

The spongy erectile tissue within the three cylinders consists of a mass of smooth muscle, often referred to as trabecular smooth muscle, within which is embedded a network of endothelial lined vascular spaces called sinusoids or lacunar spaces.

Surrounding each of the corpora cavernosa is the tunica albuginea, a dense, multi-layered, collagenous sheath that gives the penis flexibility, rigidity and tissue strength. During an erection, one layer of the tunica albuginea stretches lengthways, which allows the penis to become longer, and the other layer stretches crossways, which allows the penis to become thicker. The third cylinder, the corpus spongiosum, is outside the tunica albuginea and does not become rigid. In addition, all three cylinders are covered by a second, less-dense sheath called Buck's fascia.

Penile Blood Supply

Blood supply to the penis originates from the right and left internal arteries. These arteries are branches of the major blood supply to the pelvis and in turn branch into the deep penile artery that supplies the corpora cavernosa through small vessels known as Helisine arteries or arterioles. In the flaccid state, the small arterioles are contracted and restrict the arterial inflow into the lacunar spaces. In the erect state, relaxation of the small Helisine arteries allows a rapid increase in blood inflow and exposure of the lacunar spaces (sinusoids) to systemic blood pressure. Another branch of the penile artery, the dorsal artery, supplies the glans and the penile skin. The third branch, the bulbourethral artery, supplies the corpus spongiosum.

The most important feature of the venous drainage system is that the tunica albuginea a network of veins, the sinusoidal venules from the lacunar spaces, drains the erectile cylinders when the penis is flaccid. These subtunical venules merge to form emissary venules that exit through the tunica albuginea and pass into the larger venous system, both deep and near the surface. During erection, this network is compressed and stretched by trabecular smooth muscle relaxation. The flow of blood in is strong, the flow out of blood is weak, and the result is an erection.

Neurophysiology of Penile Erection

An erection (tumescence) is a neurovascular event, meaning that both the nervous and the circulatory systems are involved. Recent research has identified specific spots in the brain as the integration centers for sexual drive and sexual arousal, perhaps triggered by psychological factors such as erotic fantasies or expectations. Sensory factors such as audiovisual stimulation also have input through these same brain centers. The brain then controls the penis through two kinds of nerves, autonomic and somatic.

Autonomic nerves are not controlled by the individual and are "automatic" in their timing and function. There are two types: parasympathetic and sympathetic. The parasympathetic nerve fibers originate from the sacral spinal cord, at levels 2, 3 and 4 (S2-4). The sacral parasympathetic input initiates erections. The sympathetic nerves meanwhile originate from the eleventh and twelfth thoracic levels of the spinal segments, as well as the first and second lumbar spinal segments. This thoracolumbar sympathetic pathway controls detumescence and orgasm. In other words, parasympathetic autonomic nerves get it up; sympathetic autonomic nerves let it down and keep it down. As we shall see, complex chemical interactions are involved in this process, which is where Viagra comes into play.

Somatic nerves control sensory and motor functions of the body. Sensory receptors on the glans penis and the penile skin lead to sensory nerves that converge to form the primary dorsal nerve of the penis; this becomes the pudendal nerve which courses up to the sacral segments S2, 3,4.

As noted above, during an erection the penis is transformed from a venous to an arterial organ. Blood flow into the penis is controlled by three neurotransmitter systems: adrenergic nerve fibers; cholinergic nerve fibers; and nonadrenergic-noncholoinergic (NANC) fibers that release nitric oxide (NO). The exact nerve-chemical processes are very complex.

Expressed in its simplest terms, in the body, certain smooth muscle cells (those muscles we cannot control, as opposed to skeletal muscles) respond to chemical signals released by different nerves. In the penis, these chemicals normally keep the penile erectile tissue in the flaccid condition by keeping the smooth muscle cells contracted. But when the conscious or unconscious brain begins to be sexually stimulated, other chemicals are manufactured, which react with the penile erectile tissue (primarily smooth muscle cells) to set up the sequence of events that leads to an erection.

Thus, a series of coordinated vascular events, controlled by autonomic nerves, leads to an erection: relaxation of the smooth muscle in the sinusoids in the corpus cavernosum; increased arterial inflow; and occlusion of the venous drainage from within the erectile spaces. In addition to the vascular components of an erection, there are skeletal-muscular components as well, which are controlled by the somatic (sensory and motor) nerves. These skeletal components play a role in the rigid erection phase.

You can see the interplay of all these actions in the following summary of the phases of erection:

FLACCID PHASE: When the penis is resting, the trabecular smooth muscle within the corpus cavernosum is contracted and arterial blood inflow is minimal, while venous outflow is quite rapid. The blood pressure in the intracorporal space is therefore low, about 4-6 mm of Hg.

INITIAL FILLING PHASE: The parasympathetic nerve stimulation now relaxes the smooth muscle of the small arteries and arterioles resulting in a four to tenfold increase of arterial flow into the penis. Simply put, the penis is rapidly filling up with blood. The increased blood volume in the sinusoids initiates the venous occlusion process due to the stretching of the small veins below the tunica albuginea surface. In this initial filling phase there is very little change in pressure within the two corpora cavernosa.

TUMESCENCE PHASE: In this phase the volume of blood progressively increases and the pressure begins to increase inside each corpus cavernosum. The clamping down of the small veins below the tunica albuginea continues as the pressure increases. As the overall pressure builds up inside the erectile cylinders, the arterial inflow begins to diminish.

FULL ERECTION PHASE: In this phase the trabecular smooth muscle is fully relaxed and the corpus cavernosum is full with newly infused arterial blood. The arterial inflow is now minimal. The penis is rigid. The venous occlusion mechanism is in full force with no venous drainage. The pressure inside the corpus cavernosum is equal to the average arterial pressure, about 100 mm of Hg.

RIGID ERECTION PHASE: During this phase the pressure inside the corpora cavernosa may temporarily increase to several hundred mm of Hg due to contraction of the pelvic floor muscle outside the penis (ischiocavernosus muscle). Arterial inflow is still zero. The somatic penile nerves, primarily in the engorged, supersensitive glans penis, contribute to the sacral nerves to stimulate the pudendal motor nerve which is responsible for contraction of both the ischiocavernosus and bulbocavernosus muscles. A rhythmic contraction of the latter muscle is necessary for ejaculation.

DETUMESCENCE PHASE: Sympathetic (adrenergic) stimulation causes contraction of the trabecular smooth muscle. Very rapidly the venous outflow is re-established. The penis then returns to the flaccid phase.

Keep in mind that the major elements of the erection process are occurring in the two erectile cylinders, the corpora cavernosa. During erection, blood flow certainly also increases to the corpus spongiosum tissue around the urethra and to the glans penis. However, the absence of any tunica albuginea in the covering of the glans penis and the presence of only a very thin tunica covering over the corpus spongiosum means there is no significant venous occlusion. Without the thick tunica covering against which the blood veins of the corpora cavernosa are flattened, there is little increased pressure in the glans and in the third penile cylinder. But, during the rigid erection phase, contraction of the ischiocavernosus muscle and bulbocavernosus muscle do compress the spongiosum and penile veins and result in a measurable change in warmth and tone in the head of the penis.

Nerve/Chemical Interaction With Erectile Tissue

Adrenergic nerves constrict penile blood vessel and corpora cavernosum smooth muscle via alpha-1 adrenoreceptors. Norepinephrine is the neurotransmitter. Blood vessel and smooth muscle relaxation are controlled by cholinergic (with acetylcholine as a neurotransmitter from parasympathetic nerves) and nonadrenergic-noncholinergic (NANC) fibers. Some of the NANC fibers may contain vasoactive intestinal polypeptide. Vasodilation of the penile vascular structures, from primarily cavernous smooth muscle relaxation, following activation of cholinergic and NANC fibers is mediated by nitric oxide and its second messenger cyclic guanosin monophosphate (CGMP).

Second-messenger molecules like cGMP function at the molecular level inside the cell in which they reside, in this case the smooth muscle of the corpora cavernosum. We now see that the NANC neurotransmitter nitric oxide (NO) is critical in producing smooth muscle relaxation and penile erection. NO production (synthesis) results from activation of neurogenic and to a small degree, endothelial NO synthase. Once NO diffuses into the smooth muscle cell, it binds to an enzyme guanylyl cyclase. This causes an increase in guanylyl cyclase activity, resulting in cyclic GMP (cGMP) production or synthesis. This intracellular second messenger then carries out the final step in relaxing smooth muscle, reducing the level of intracellular calcium by binding to cGMP-dependent protein kinases, cGMP-dependent ion channels, and cGMP-regulated phosphodiesterases. The overall amount of intracellular cGMP, is controlled by and regulated by the activity of the phosphodiesterase 5, which helps convert cGMP back to GMR Several other forms of phophodiesterase (PDE) have been identified in penile tissue (types 2, 3, 4 and 5); however, PDE 5 is the predominant phosphodiesterase in human corpus cavernosum and human corpus cavernosa smooth muscle. It also is apparently located just in human penile tissue. Viagra functions to block PDE 5. This allows cGMP levels to remain high and continue their function as a smooth muscle relaxant that potentiates and maintains the penile erection.