For these changes to happen, teamwork from the brain, blood vessels, nerves, and hormones is needed. When the individual senses something as arousing, erection begins.
Nerve stimulation relaxes the blood vessels in the corpora, making more room for blood.
Like a sponge, the corpora fill with blood. The penis swells, but is not yet rigid enough for intercourse. As the corpora continue to swell, they press against the veins, keeping blood from leaving the penis. Blood is trapped in the spongy tissue of the corpora. Full of blood, the corpora become rigid and erect making the penis rigid enough for intercourse.