[Regulation of male sexual function]

MECHANISM OF ERECTION: Commands transmitted from the brain to the spinal cord during audiovisual sexual stimulation and sexual fantasy cause excitation of the central erection-related nerves of the spinal cord, which transmit the commands to the corpora cavernosa. As a result, the following sequence of phenomena takes place: 1) The cavernosal and helical arterioles dilate and the volume of blood in the lacunar spaces increases. 2) The cavernosal smooth muscle relaxes and the vascular lacunae expand. 3) Extension of the lacunar spaces causes compression of the veins below the albuginea corpora cavernosa of the penis. MECHANISM OF EJACULATION: The mechanism of ejaculation can be divided broadly into two stages. In the first stage, seminal emission to the posterior urethra and closure of the internal urethral opening are occurred by stimulation of the hypogastric nerve. The second stage of ejaculation, which is projectile ejaculation of the semen from the posterior urethra, occur as the result of a spinal reflex via the pudendal nerve. For this sequence of events to occur, simultaneous stimulation from the hypogastric nerve is required.