Male Sexual Response and Erectile Physiology

The male sexual response is a neurovascular sequence in which sexual stimulation triggers relaxation of penile smooth muscle, arterial inflow, and venous trapping that produce erection, followed by emission, ejaculation, orgasm, and detumescence. Its central mechanism is nitric-oxide-mediated relaxation of cavernosal smooth muscle under parasympathetic and somatic neural control, set against a sympathetically maintained flaccid baseline.

Definition

The male sexual response is the coordinated sequence of penile erection (vasocongestion from neurally mediated smooth-muscle relaxation), emission and ejaculation, orgasm, and detumescence that constitutes the physiological male sexual response cycle.

Scope

This topic covers the physiological events of the male sexual response cycle — arousal and erection, emission and ejaculation, orgasm, and resolution — and the smooth-muscle and signalling mechanisms (notably the nitric oxide / cyclic GMP pathway) that drive penile tumescence. It is reference physiology of normal function, with vascular anatomy treated in the companion penile-physiology topic and central pathways in the neural-control topic.

Core questions

• How does neural stimulation produce erection through smooth-muscle relaxation and altered penile haemodynamics?
• What is the role of nitric oxide and cyclic GMP in initiating and sustaining tumescence?
• How are emission and ejaculation organized and distinguished from orgasm?
• What maintains the flaccid state and drives detumescence after orgasm?

Key concepts

• Erection (tumescence) and detumescence
• Cavernosal smooth-muscle relaxation
• Nitric oxide / cyclic GMP signalling
• Veno-occlusive mechanism
• Emission and antegrade ejaculation
• Orgasm and the refractory period
• Sympathetic flaccid tone

Mechanisms

In the flaccid penis, tonic sympathetic activity and contracted cavernosal smooth muscle keep arterial inflow low. Sexual stimulation releases nitric oxide from parasympathetic nitrergic nerves and endothelium; nitric oxide activates guanylate cyclase, raising cyclic GMP, which relaxes trabecular and arterial smooth muscle. Arterial inflow rises, the expanding sinusoids compress subtunical venules against the tunica albuginea (the veno-occlusive mechanism), and trapped blood produces rigid erection. Emission — deposition of seminal fluid into the posterior urethra — is sympathetically mediated, and rhythmic contractions of the bulbospongiosus and other perineal muscles, driven by somatic pudendal pathways, expel semen during ejaculation; orgasm is the accompanying central sensory experience. Sympathetic discharge and phosphodiesterase-mediated breakdown of cyclic GMP then restore smooth-muscle tone and detumescence.

Clinical relevance

Because erection depends on an intact vascular supply, smooth-muscle and endothelial function, and autonomic and somatic innervation, the same mechanisms that produce normal erection are the framework for understanding erectile and ejaculatory disorders. This entry describes normal physiology for orientation and is not guidance for evaluating or treating any individual.

Evidence & guidelines

The physiology summarized here is drawn from widely cited reviews of erectile mechanism and pharmacology and of ejaculatory physiology. These are mechanistic and narrative syntheses rather than clinical practice guidelines.

History

The neurovascular model of erection was established through haemodynamic and pharmacological studies in the late twentieth century, with the discovery of nitric oxide as the principal mediator of cavernosal smooth-muscle relaxation reframing both the physiology and its pharmacology. Subsequent reviews integrated emission and ejaculation, including their serotonergic central control, into a unified account of the male sexual response.

Key figures

• Tom Lue
• Karl-Erik Andersson
• Arthur Burnett
• Francois Giuliano

Seminal works

• lue-2000
• andersson-2011
• burnett-2002

Frequently asked questions

What actually makes the penis rigid during erection?

Neurally released nitric oxide relaxes cavernosal smooth muscle, arterial inflow rises, and the expanding sinusoids compress the draining veins against the tunica albuginea, trapping blood and producing rigidity (the veno-occlusive mechanism).

Are orgasm and ejaculation the same thing?

No. Ejaculation is the physiological expulsion of semen, organized as emission (sympathetic) followed by rhythmic perineal muscle contractions (somatic); orgasm is the central sensory and affective experience that usually accompanies it but is mechanistically distinct.