File:Male Orgasm Response showing Involuntary Anogenital Muscular Contractions.webm

English: Orgasm of 44 year old caucasian male, induced by manual self stimulation, showing externally the involuntary rhythmic contractions of the Anal Sphincters and Bulbospongiosus Muscle (perineal) at regular intervals. Along with synchronized contractions of internal structures including the Prostate, Semen is expelled from the body via the Urethra. Here, seventeen (17) rhythmically spaced involuntary muscular contractions of the anus and surrounding structures are visible. The contractions are rapid at first, then at fairly even intervals three through eight (3-8), gradually slowing after that. Ejaculation began with the first contraction (0:05); the largest volume was expelled during contractions two through four (2-4), with significant amount of ejaculate continuing to be expelled through at least the ninth (9th) contraction, though with gradually less force and volume. Nominal amount of semen is expelled with subsequent contractions, which are spaced at gradually longer intervals. Numerous muscular contractions from the seventeenth (17th) contraction onward (not shown) become more irregular and lacked significant volume of ejaculate, if any. Approximately 4.0-4.5ml of ejaculate was measured. Just before orgasm begins, you can see the testicles retract toward the abdominal cavity and the anal sphincters relax and open (0:03) as orgasm becomes imminent. When orgasm begins, ejaculation and contractions are involuntary and cannot be stopped or controlled until the process resolves.