This may result from any of various physiological stimuli, also known as sexual stimulation and sexual arousal. Īn erection occurs when two tubular structures, called the corpora cavernosa, that run the length of the penis, become engorged with venous blood. After reaching puberty, erections occur much more frequently. Side views and comparison of the stages of an uncircumcised (top and bottom) and a circumcised (middle) human penis erectionĪn erection is necessary for natural insemination as well as for the harvesting of sperm for artificial insemination, and is common for children and infants. The state of a penis which is partly, but not fully, erect is sometimes known as semi-erection (clinically: partial tumescence) a penis which is not erect is typically referred to as being flaccid, or soft. Absence of nocturnal erection is commonly used to distinguish between physical and psychological causes of erectile dysfunction and impotence. Erections during sleep or upon waking up are known as nocturnal penile tumescence (NPT), also known as 'morning wood'. Erection subsides when parasympathetic activity reduces to baseline.Īs an autonomic nervous system response, an erection may result from a variety of stimuli, including sexual stimulation and sexual arousal, and is therefore not entirely under conscious control. The arteries dilate causing the corpora cavernosa of the penis (and to a lesser extent the corpus spongiosum) to fill with blood simultaneously the ischiocavernosus and bulbospongiosus muscles compress the veins of the corpora cavernosa restricting the egress and circulation of this blood. Physiologically, an erection is required for a male to effect penetration or sexual intercourse and is triggered by the parasympathetic division of the autonomic nervous system, causing the levels of nitric oxide (a vasodilator) to rise in the trabecular arteries and smooth muscle of the penis.

The shape, angle, and direction of an erection vary considerably between humans. Penile erection is the result of a complex interaction of psychological, neural, vascular, and endocrine factors, and is often associated with sexual arousal, sexual attraction or libido, although erections can also be spontaneous. An erection (clinically: penile erection or penile tumescence) is a physiological phenomenon in which the penis becomes firm, engorged, and enlarged.

Sims 3 child penis mod