The excitement of cerebral cortex spreads through the erection center of thoracic and lumbar spinal cord, acts on the cavernous body of penis, dilates arterial blood vessels, and a large amount of blood flows into the cavernous body of penis; Venous vessels contract, and the blood flowing out of cavernous body decreases. In this way, the blood will fully stay in the rich blood vessels and blood sinuses in the cavernous body, making the penis erect.
This kind of erection, which is excited by sight, hearing and imagination and acts on the penis, is called mental erection. In addition, due to local stimulation, such as touching external genitalia, rubbing shorts when walking, or stimulating rectum and bladder (such as inflammation), it can also cause congestion of penis blood vessels and blood sinuses through sacral nerve. This kind of erection caused by local direct stimulation is called reflex erection. ?
Whether it is a mental erection or a reflex erection, when the external stimulus is removed, the arteries of the cavernous body of the penis contract, the veins are opened, the excess blood stranded in the penis will flow out, and the penis will return to normal, thus completing the whole process from erection to weakness.