Physiology of Emission, Ejaculation, & Orgasm

Different mechanisms are involved in erection, emission, ejaculation, and orgasm, and these events can be dissociated from one another (eg, a frequent complaint of impotent patients is ejaculating through a “limp penis”). Except for nocturnal emissions, or “wet dreams,” emission and ejaculation require stimulation of the external genitalia. Impulses traveling from the pudendal nerves reach the upper lumbar spinal sympathetic nuclei. Efferent signals traveling in the hypogastric nerve activate secretions and transport sperm from the distal epididymis, vasa deferentia, seminal vesicles, and prostate to the prostatic urethra. Coordinated closing of the internal urethral sphincter and relaxation of the external sphincter direct the semen into the bulbous urethra (emission). Subsequent rhythmic contractions of the bulbocavernous muscles force the semen through a pressurized conduit - the much narrowed urethral lumen compressed by the engorged corpora cavernosa - to produce the 2- to 5-mL ejaculate. The external ejaculation process involves the somatomotor efferent of the pudendal nerve to contract the bulbocavernous muscle. Since this action is involuntary, however, integrated autonomic and somatic action is required.

The mechanism of orgasm is the least understood of the sexual processes. It probably involves cerebral interpretation and response to sexual stimulation. Along with emission and ejaculation, several nongenital responses also occur. These include involuntary rhythmic contractions of the anal sphincter, hyperventilation, tachycardia, and elevation of blood pressure.