Erection
Erection (clinically, penile erection or penile tumescence) is a physiological phenomenon in which the penis becomes firm, engorged and enlarged. Penile erection is a complex interaction of psychological, neural, vascular and endocrine factors. It is generally accompanied by sexual arousal, sexual attraction or libido. However, erections may occur without sexual arousal. The form, angle and direction of an erection varies greatly between humans.
Physiologically, an erection is necessary for a male to achieve penetration or sexual intercourse and is initiated by the parasympathetic division of the autonomic nervous system, resulting in a rise in levels of nitric oxide (a vasodilator) in the trabecular arteries and smooth muscle of the penis. The arteries dilate, causing the corpora cavernosa of the penis (and to a lesser extent the corpus spongiosum) to fill with blood; at the same time the ischiocavernosus and bulbospongiosus muscles compress the veins of the corpora cavernosa, thereby limiting the egress and circulation of this blood. Erection subsides as parasympathetic activity drops back to baseline.
Erections are a response of the autonomic nervous system to many types of stimuli, including sexual stimulation and sexual arousal, and therefore are not completely voluntary. Nocturnal penile tumescence (NPT), or “morning wood” refers to erections during sleep or when waking up. Nocturnal erection is often used to distinguish between physical and psychological causes of impotence and erectile dysfunction.
A penis which is partly but not fully erect is sometimes known as a semi-erection (clinically: partial tumescence). A penis which is not erect is usually referred to as being flaccid, or soft.
See Also
- Prostitution | Prostitute | Hooker | Pimp
- Gay porn | Gay | Bisexuality
