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Male Sexual Response: Erection & Ejaculation
Sexual stimulation can take various forms, such as physical touch and visual or auditory cues. When this happens, the parasympathetic reflex in the sa…
In response to the sexual stimuli, the parasympathetic neurons stimulate the local release of nitric oxide, or NO, dilating the arterioles in the penis. This increases blood flow into the erectile tissues — the corpora cavernosa and corpus spongiosum.
The blood filling the erectile tissues compresses the veins to prevent blood from leaving the penis.
As a result, the penis becomes engorged and rigid, leading to an erection.
At the critical point of sexual arousal, a spinal reflex coordinated by the sympathetic fibers in the lumbar region triggers ejaculation.
This reflex causes coordinated contractions of the epididymis, vasa deferens, seminal vesicles, and prostate gland, propelling semen into the prostatic urethra.
After the semen enters the penis, muscles like the bulbospongiosus and the ischiocavernosus in the pelvic floor contract.
These contractions of the ducts, glands, and muscles forcefully expel semen from the urethra to the exterior in a process called ejaculation.
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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.