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Ejection of the seminal fluid from the male urethra.

Ejaculation consists of two phases: (1) the passage of semen and the secretions of the accessory organs (bulbourethral and prostate glands and seminal vesicles) into the urethra and (2) the expulsion of the seminal fluid from the urethra. The former is brought about by contraction of the smooth muscle of the ductus deferens and the increased secretory activity of the glands, the latter by the rhythmical contractions of the bulbocavernosus and ischiocavernosus muscles and the levator ani. The prostate discharges its secretions before those of the seminal vesicle. The sensations associated with ejaculation constitute the male orgasm. Ejaculation occurs without ejection of the seminal fluid from the male urethra in patients who have had a prostatectomy. In that case, the ejaculate is in the bladder.

Ejaculation is a reflex phenomenon. Afferent impulses arising principally from stimulation of the glans penis pass to the spinal cord by way of the internal pudendal nerves. Efferent impulses arising from a reflex center located in the upper lumbar region of the cord pass through sympathetic fibers in the hypogastric nerves and plexus to the ductus deferens and seminal vesicles. Other impulses arising from the third and fourth sacral segments pass through the internal pudendal nerves to the ischiocavernosus and bulbocavernosus muscles. Erection of the penis usually precedes ejaculation. Ejaculation occurs normally during copulation or masturbation or as a nocturnal emission. The seminal fluid normally contains 60 million to 150 million sperm/mL. The volume of the ejaculation is from 2 to 5 mL.
SEE: orgasm; SEE: semen

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