The mechanism of human penile erection lies in the increase of blood flow in the arteries of the pubic region and the obstruction of venous return, which in turn triggers an erection. The causes of erection are mainly categorized as neurological, spontaneous and psychological.
1. Nerve reflex: Reflex erection is a nerve reflex triggered by external stimulation of the tissues and muscles around the penis, while the basilar and suspensory ligaments at the root play a role in supporting and maintaining the erectile state.
2. Nocturnal spontaneous erection: It occurs automatically during night sleep, especially during rapid eye movement sleep, and normal men have it about three times or more a night. The mechanism of spontaneous erection is not clear, it may be related to the release of inhibition of higher centers and parasympathetic re-excitation.
3. Psychological: Neural reflexes triggered by brain stimulation signals in hearing, vision or fantasy.