Physiology of sexual function

The mechanisms of nervous regulation seem to be very complex due to their special dependence on various influences of the external environment, mediated by social factors. However, despite all their complexity, they are carried out on the basis of general principles of reflex activity. The material substrate is receptors, afferent pathways, sexual centers at different levels of the central nervous system and efferent conductors to the sexual 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, as well as for solving practical issues of diagnosis and treatment.

Efferent sympathetic fibers from the rostral lumbar spinal cord innervate the vas deferens, seminal vesicles, and prostate gland, passing through the subventricular plexus. Stimulation of this plexus causes ejaculation. The ejaculation center, or sexual sympathetic center, is located in the upper lumbar segments of the spinal cord. The erection center, or sexual parasympathetic center, is located in the lateral horns of the sacral segments SII - SIV. The parasympathetic fibers coming from it are efferent vasodilator nerves of the vessels of the penis and contribute to the occurrence of an erection, causing dilation of the arteries and an increase in pressure in the cavernous tissues. On their way, these fibers are interrupted in the plexus of the prostate gland. The striated bulbocavernous and spongiocavernous muscles, which facilitate the release of seminal fluid from the urethra, are innervated by the somatic pudendal nerves (nn. pudendi).

In women, the activation of predominantly parasympathetic mechanisms leads to sexual arousal - erection of the clitoris, spongy body of the urethra, cavernous body of the vestibule bulb, tension of the cavernous muscles and secretion of the Bartholin glands, which characterizes the readiness of the genitals for copulation. Subsequent increasing excitation of sympathetic regulatory mechanisms leads to the emergence of a motor orgasmic complex.

From the above it is clear that the involvement in the pathological process of the nerves that control each phase of the sexual response in men and women leads to a violation of sexual function.

The closest area where subcortical regulation of sexual function is carried out is the hypothalamic. It is currently believed that sympathetic and parasympathetic cellular structures are differentiated in the hypothalamus, connected with a wide network of diverse afferent pathways carrying impulses from the external environment, from receptors of internal organs, and also from various parts of the brain. There are also special efferent pathways (hypothalamic-spinal) going from the hypothalamus to the area of the cerebral aqueduct 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 unite sexual activity with other organs and systems: cardiovascular, endocrine, thermoregulatory, etc. These apparatuses are represented in the limbic-reticular system of the brain. All activities of the organism to optimally ensure sexual function are carried out due to the integrative activity of the limbic-reticular system through its ergotropic and trophotropic mechanisms. Ergotropic zones (mesencephalon and posterior hypothalamus) ensure adaptation to changing environmental influences, using mainly sympathetic segmental apparatuses; trophotropic zones (rencephalon, anterior hypothalamus and caudal part of the trunk) restore and maintain the constancy of the internal environment of the organism (homeostasis), using mainly parasympathetic apparatuses for this purpose.

The hypothalamic specific system regulating the gonadotropic function of the pituitary gland is considered to be the paraventricular and ventromedial nuclei, related to the parvocellular region of the gray tubercle. When the gray tubercle is destroyed, sexual function is impaired and the gonads atrophy.

Observations of patients with organic brain damage show the unequal role of the right and left hemispheres in regulating sexual function. Patients with extensive damage to the dominant hemisphere develop serious speech disorders and paralysis of the opposite limbs, but sexual function either does not suffer or suffers only due to the weakening of general (somatic) health. Damage to the subdominant hemisphere, even less extensive, almost always leads to a disorder of sexual function along with peculiar emotional disturbances and paralysis of the opposite limbs.

Conditioned reflex sexual stimuli, without which normal sexual function is impossible, are perceived primarily by the cortex of the right hemisphere. The cortex of the left hemisphere carries out primarily inhibitory second-signal effects on cortical first-signal (excitatory) sexual impressions and on subcortical emotional-vegetative regulatory mechanisms.

Unconditioned reflex regulation is innate; it serves as the basis for the formation of higher conditioned reflex regulatory mechanisms and is subject to their influence during sexual activity.

Thus, the nervous regulation of sexual function is a dynamic functional system that unites the cellular structures of different levels of the nervous system into a single regulatory mechanism.

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