Smooth muscle in the duct system of the male reproductive tract and in the accessory glands is innervated by sympathetic fibers from the lower thoracic and upper lumbar spinal levels (T12, L1,2). The fibers pass into the prevertebral plexus and are then distributed to target tissues. Semen is formed as luminal contents from the ducts (epididymis, ductus deferens, ampulla of the ductus deferens) and glands (prostate, seminal vesicles) are moved into the urethra at the base of the penis by the contraction of smooth muscle in the walls of the structures.