31.10
Risposta sessuale maschile: erezione ed eiaculazione
La stimolazione sessuale può assumere varie forme, come il contatto fisico e segnali visivi o uditivi. Quando ciò accade, viene attivato il riflesso p…
In risposta agli stimoli sessuali, i neuroni parasimpatici stimolano il rilascio locale di ossido nitrico, o NO, dilatando le arteriole del pene. Questo aumenta il flusso sanguigno nei tessuti erettili, i corpi cavernosi e i corpi spongiosi.
Il sangue che riempie i tessuti erettili comprime le vene per evitare che il sangue lasci il pene.
Di conseguenza, il pene diventa gonfio e rigido, portando all'erezione.
Nel punto critico dell'eccitazione sessuale, un riflesso spinale coordinato dalle fibre simpatiche nella regione lombare innesca l'eiaculazione.
Questo riflesso provoca contrazioni coordinate dell'epididimo, dei vasi deferenti, delle vescicole seminali e della ghiandola prostatica, spingendo lo sperma nell'uretra prostatica.
Dopo che lo sperma è entrato nel pene, muscoli come il bulbospongioso e l'ischiocavernoso nel pavimento pelvico si contraggono.
Queste contrazioni dei dotti, delle ghiandole e dei muscoli espellono con forza lo sperma dall'uretra verso l'esterno in un processo chiamato eiaculazione.
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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.