Orgasm, or orgasm for short, is usually a wonderful feeling that occurs during sex between a man and a woman, a physical and psychological experience, and the most important stage in the process of sexual intercourse. During the male orgasm, the sexual organs begin a series of contractions that cause semen to pool in the prostate part of the urethra. Semen originates from three different organs: the prostate gland, the seminal vesicles and the vas deferens. During the first stage of the ejaculatory process, when the man perceives a dynamic change in the pressure that serves as the beginning of ejaculation, he experiences a feeling of inevitability of ejaculation. Several seconds pass between the beginning of ejaculation and the ejaculation of semen out of the body because, on the one hand, ejaculation must pass this distance through the urethra; on the other hand, it takes time to gather enough contraction pressure in order to advance the semen that has been collected. The internal sphincter at the top of the urinary bladder closes tightly during ejaculation to ensure that a large amount of fluid is propelled toward the path of least resistance. Semen is ejected rhythmically through the urethra, less than once a second, four to five times in a row. The ejaculatory process is accomplished by rhythmic contractions of the prostate, perineal muscles, and penile body together in concert.