Sexual stimulation initiates impulses, leading to of arterioles and of venules supplying the erectile tissue. These vascular changes produce an , which permits placing the urethral opening near the opening of the cervix. Just before ejaculation, impulses stimulate contractions of the epididymis, , and ejaculatory ducts, leading from each testicle, and contractions in the accessory glands. Continued sexual stimulation of the glans leads to an , which is characterized by of semen with rhythmic contractions of located at the base of the penis. Immediately after ejaculation, impulses cause of arterioles and of venules supplying the erectile tissue, and the penis becomes flaccid. While the the two nervous systems generally act in opposite ways,