What is an erection?

Getting an erection is a complex process that involves physical, hormonal, neurological, and psychological factors. The penis is made up of soft, spongy, elastic tissue that fills with blood, causing it to increase in size and become firm.
Around the spongy tissue and the prostate, there are nerves that send signals so that the blood vessels supply more blood to the penis (Fig. 1). These signals are influenced by several factors, including the male hormone testosterone.