How does an erection work and why do they happen spontaneously sometimes
Erection is the scientific term for that state of the penis when the two corpora cavernosa (two tubular muscles) are filled with blood. This means that the penis hardens and grows in length to accommodate the extra blood.
Penile erection is usually the result of sexual stimulation, but is also known to occur spontaneously, most commonly at night, during erotic dreams. Erection in males can be caused by mechanical stimulation, or by the pressure of the bladder, when full. The exact cause of spontaneous erections is not known. The erection is crucial to sexual intercourse and most other sexual activities for males.