31.10
Réponse sexuelle masculine : érection et éjaculation
La stimulation sexuelle peut prendre diverses formes, comme le toucher physique et les signaux visuels ou auditifs. Lorsque cela se produit, le réflex…
En réponse aux stimuli sexuels, les neurones parasympathiques stimulent la libération locale d’oxyde nitrique, ou NO, dilatant les artérioles du pénis. Cela augmente le flux sanguin dans les tissus érectiles - les corps caverneux et les corps spongieux.
Le sang qui remplit les tissus érectiles comprime les veines pour empêcher le sang de quitter le pénis.
En conséquence, le pénis devient engorgé et rigide, conduisant à une érection.
Au point critique de l’excitation sexuelle, un réflexe spinal coordonné par les fibres sympathiques de la région lombaire déclenche l’éjaculation.
Ce réflexe provoque des contractions coordonnées de l’épididyme, du canal déférent, des vésicules séminales et de la prostate, propulsant le sperme dans l’urètre prostatique.
Une fois que le sperme a pénétré dans le pénis, des muscles comme le bulbo-spongiosus et l’ischiocaverneux du plancher pelvien se contractent.
Ces contractions des conduits, des glandes et des muscles expulsent avec force le sperme de l’urètre vers l’extérieur dans un processus appelé éjaculation.
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Q1: How does nitric oxide cause an erection?
Sexual stimulation activates parasympathetic neurons that release nitric oxide in the penis. Nitric oxide dilates the arterioles, increasing blood flow into the erectile tissues—the corpora cavernosa and corpus spongiosum. The blood filling these tissues compresses the veins, preventing blood from leaving and causing the penis to become engorged and rigid.
Q2: What role do the accessory glands play in ejaculation?
During ejaculation, a sympathetic reflex triggers coordinated contractions of the accessory glands of the male reproductive system, including the seminal vesicles and prostate gland. These contractions propel semen into the prostatic urethra in a process called emission, which precedes the forceful expulsion of semen from the body.
Q3: What is the difference between emission and ejaculation?
Emission occurs when sympathetic fibers in the lumbar spine trigger contractions of the epididymis, vasa deferens, seminal vesicles, and prostate, propelling semen into the prostatic urethra. Ejaculation follows when pelvic floor muscles like the bulbospongiosus and ischiocavernosus contract, forcefully expelling semen from the urethra to the exterior.
Q4: Which spinal nerves control the male sexual response?
Parasympathetic fibers in the sacral portion of the spinal cord initiate erection by stimulating nitric oxide release. Sympathetic fibers located in the lumbar region, typically at T12-L2, coordinate the reflex that triggers ejaculation through contractions of reproductive ducts and glands.
Q5: How do pelvic floor muscles contribute to ejaculation?
During ejaculation, pelvic floor muscles including the bulbospongiosus and ischiocavernosus contract forcefully around the urethra. These muscular contractions expel semen from the penis to the exterior, completing the ejaculatory process after semen has entered from the accessory ducts of the male reproductive system.
Q6: What prevents blood from leaving the penis during an erection?
As blood fills the erectile tissues—the corpora cavernosa and corpus spongiosum—it exerts pressure that compresses the veins in the penis. This compression prevents venous outflow, trapping blood within the erectile tissues and maintaining the rigid, engorged state characteristic of an erection.
Q7: What types of sexual stimuli trigger the parasympathetic reflex?
Sexual stimulation can take various forms, including physical touch and visual or auditory cues. Any of these stimuli activate the parasympathetic reflex in the sacral portion of the spinal cord, which initiates nitric oxide release and the cascade of physiological events leading to erection.