How does an erection work and what are the physiological processes involved in achieving and maintaining it?

An erection is a complex physiological process that involves the nervous system, blood vessels, and hormones. When a man becomes sexually aroused, the brain sends signals to the nerves in the penis, causing the blood vessels to relax and widen. This allows more blood to flow into the penis, filling the spongy tissue called the corpora cavernosa. As the tissue fills with blood, the penis becomes erect and hard. To maintain the erection, the blood vessels constrict to trap the blood in the penis, and the nerves release chemicals that help sustain the erection. After ejaculation or when sexual arousal decreases, the blood flows out of the penis, and the erection subsides.