Fellowship in Sexology and Psychosexual Counseling. For More Info WhatsApp- 9604715783/9359863878. At this point ejaculation cannot be stopped. In the second stage of orgasm contraction of urethra and penis combined with contractions in the prostate to cause ejaculation (spurting of semen out of tip of penis.) During ejaculation the neck of the urinary bladder is tightly shut to avoid any mixture of semen and urine. The rhythmic contractions of prostate, the perineal muscles and the penis occur initially at 0.8 second intervals.