The male erectile response is vascular event initiated by neuronal action and maintained by a complex interplay between vascular and neurological and perhaps hormonal phenomenon resulting in a cascade of events.

   Physiology of the erection and ejaculation is comparable to combination of electrical and plumbing events. The electrical system consists of the areas of brain and spinal cord regulating male sexual response and peripheral nervous system. The electrical system provides stimulus for the plumbing system that consist of a series of arteries and veins controlling inflow and outflow of blood to and fro from penis.

Phases of male sexual cycle

1.    Desire (libido)-fantasies, thoughts, feelings.
2.    Excitement –pleasure, erection.
3.    Orgasm –emission and ejaculation.
4.    Resolution- relaxation, refractory period

Erection 

It has 3 types of origin

1. Psychogenic

It is initiated by erotic thought in brain from where the impulse passes on to spinal center at the thoraco-lumbar and sacral segment of the spinal cord to  set up erectile process.

2. Reflexogenic

It is caused by tactile stimulus from the glans reaching the spinal center to initiate reflex activity.

3. Nocturnal

It is initiated during rapid eye movement sleep phase in the pontine reticular formation where cholinergic neurons are activated while the adrenergic neurons remain silent. This impulse then passes on the spinal center to cause erection.