Normal sexual function in human body is complex. Any disruption in neurologic, vascular, endocrine, and psychiatric system may affect normal sexual and reproductive function in men.
Normal sexual function
A neuropsychological stimulus is initiated for the penile erection which causes vasodilation of the arteries in corpora cavernosa, accompanied by libido. The libido is totally androgen-dependent psychic factor for penile erection. Parasympathetic, sympathetic and some somatic fibers supplies innervations to the penis. The afferent part of the erectile reflex is formed by the somatic fibers in the dorsal nerve of the penis by transmitting sensory impulses to the dorsal root ganglia S2-S4 dorsal root ganglia.
A large number of afferent nerve endings in the glans are free, as compared to the corpuscular type endings in the penile shaft skin, thus making glans more sensitive as compared to penile shaft skin. The rhythmic contraction of epididymis, seminal vesicle, vas deferens is due to the somatic efferent fibers from S3-S4 traveling in the pudendal nerve. Some autonomic nerve fibers enter the corpus spongiosum while the remaining enter the corpura cavernosa along terminal branches of pudendal artery and cavernous veins. Damage to these nerves mat result in erectile importance.
The brain plays an important role in controlling the penile function by influencing spinal reflex pathways. Different types of imaginative, touch, visual stimuli may elicit erectile responses. The hypothalamus is an important integrating center. Other areas of the brain such as the amyglaloid complex, may inhibit sexual function.
In the flaccid stage, there is contraction of smooth muscles of arteries, arterioles and sinusoidal spaves of corpora cavernosa. These structures are constricted due to active sympathetic control. The venules between the sinusoids are freely open to the emissary veins.
When erection begins, the smooth muscles of internal pudendal artery and cavernosa are relaxed, resulting in the rapid rush of arterial blood flow. The blood is trapped in the expanding sinusoidal system, compressing the venules against the tunica albuginea, resulting in venous occlusion. This phenomenon leads to rigidity and tumescence of penis.
Ejaculation and seminal emission are under the control of sympathetic nervous system. Seminal fluid enters the prostatic urethra by alpha-adrenergic-mediated contraction of the epididymis, vas deferens, seminal vesicles and prostate. The seminal fluid enters the urethra and is poured out.
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