Men’s Health - What causes an erection?
Hormones, blood vessels, nerves, and muscles must all work together to make an erection. Your brain starts an erection by sending nerve signals to the penis when it senses sexual stimulation. Touching may cause this arousal. Another trigger may be something you see or hear. It may be a sexual thought or dream.
Your brain starts an erection by sending nerve signals to the penis.
The nerve signals cause the muscles within the penis to relax and let blood flow into the spongy tissue within the penis. Blood collects in this tissue like water filling a sponge.
The penis becomes larger and firmer and the veins then get shut off to keep blood from flowing out.
After climax, or after the sexual arousal has passed, the veins open back up and blood flows back into the body.