Physiology of sexual function
Last reviewed: 23.04.2024
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Mechanisms of nervous regulation seem very complicated due to their special dependence on various environmental influences mediated by social factors. However, for all their complexity, they are carried out on the basis of general principles of reflex activity. The material substrate is receptors, afferent pathways, sex centers at different levels of the central nervous system, and efferent conduits to the genital organs.
The question of the localization of sexual centers in the brain is of particular importance for understanding the mechanisms of regulation of sexual function, the etiology and pathogenesis of sexual disorders, and also for solving practical questions of diagnosis and treatment.
Efferent sympathetic fibers, coming from the rostral lumbar spinal cord, innervate the vas deferens, seminal vesicles and the prostate gland, passing through the pancreatic plexus. Stimulation of this plexus causes ejaculation. The ejaculation center, or genital sympathetic center, is located in the upper lumbar segments of the spinal cord. The center of an erection, or the sexual parasympathetic center, is located in the lateral horns of the sacral segments of SII-SIV. The parasympathetic fibers that go from it are the efferent vasodilator nerves of the vessels of the penis and contribute to the erection, causing the arteries to expand and increase the pressure in the cavernous tissues. On their way, these fibers are interrupted in the plexus of the prostate gland. The striped bulbokavernoznye and spongiokavernoznye muscles that facilitate the allocation of semen from the urethra are innervated by somatic pudendic nerves (nn. Rudendi).
In women, the inclusion of predominantly parasympathetic mechanisms leads to sexual arousal-the erection of the clitoris, the urethral spongy body, the cavernous body of the bulb of the vestibule, the tension of the cavernous muscles, and the secretion of the Bartholin glands, which characterizes the readiness of the reproductive organs to mate. The subsequent increasing excitation of sympathetic regulatory mechanisms leads to the appearance of a motor orgasmic complex.
From what has been said it is clear that the involvement of the nerves in the pathological process that control each phase of the sexual reaction in men and women leads to a violation of sexual function.
The nearest area where subcortical regulation of sexual function is carried out is hypothalamic. At present, it is believed that in the hypothalamus sympathetic and parasympathetic cellular structures are differentiated, connected with a wide network of diverse afferent pathways carrying impulses from the surrounding environment, from receptors of internal organs, as well as from various parts of the brain. There are also special efferent pathways (hypothalamo-spinal), which go from the hypothalamus to the region of the aqueduct of the brain and then along the central canal to the lateral horns of the spinal cord.
The presence of specific sympathetic and parasympathetic innervation of the genitals does not exclude the presence of more complex associative vegetative apparatuses that functionally combine sexual activity with other organs and systems: cardiovascular, endocrine, thermoregulatory, etc. These devices are represented in the limbic-reticular system of the brain. The whole activity of the body for the optimal maintenance of sexual function is due to the integrative activity of the limbic-reticular system through its ergotropic and trophotropic mechanisms. Ergotropic zones (mesencephalon and posterior hypothalamus) provide adaptation to changing environmental influences, using predominantly sympathetic segmental apparatuses; trophotropic zones (rin-encephalon, anterior hypothalamus and caudal trunk) restore and maintain the constancy of the internal environment of the organism (homeostasis), using mainly parasympathetic apparatuses.
A hypothalamic specific system regulating the gonadotropic function of the pituitary gland is considered to be the paraventricular and ventromedial nuclei, referring to the parvocellular region of the gray tubercle. With the destruction of the gray tubercle, there is a violation of sexual function and gonadal atrophy.
Observations of patients with organic brain lesions show the unequivalence of the right and left hemispheres in the regulation of sexual function. In patients with extensive damage to the dominant hemisphere, serious speech disorders and paralysis of the opposite limbs develop, but the sexual function either does not suffer, or suffers only in connection with the weakening of general (somatic) health. Disorders of the subdominant hemisphere, even less extensive, almost always lead to a disorder of the sexual function, along with peculiar emotional disturbances and paralysis of the opposite limbs.
Conditional-reflex sexual stimuli, without which it is impossible to perform normal sexual function, are perceived primarily by the bark of the right hemisphere. The cortex of the left hemisphere primarily carries out braking second-signal effects on cortical primary (exciting) sexual impressions and subcortical emotional-vegetative regulatory mechanisms.
Unconditionally-reflex regulation is congenital; it serves as the basis for the formation of higher conditioned-reflex regulatory mechanisms and in the process of sexual life is subordinated to their influence.
Thus, the nervous regulation of the sexual function is a dynamic functional system that combines the cellular structures of different levels of the nervous system into a single regulatory mechanism.
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