Penile erection nervous system

ED can result from an abnormality in one of the four systems necessary for a normal penile erection or from a combination of abnormalities. Vascular, nervous, or hormonal etiologies of ED are referred to as organic ED. Abnormality of the fourth system (i.e., patient s psychological receptivity to sexual stimuli) is referred to as psychogenic ED. 

Figure 19.17 The biochemistiy and physiology responsible for penile erection. Sexual activity itself begins with a state of arousal that leads to erection. Arousal results in part from stimulation of the sense organs. The hypothalamus coordinates the sensations and activates the autonomic nervous system. Sensory nerves from the skin of the penis and other erogenous zones stimulate the parasympathetic system. This activates nitric oxide synthase and the resultant nitric oxide, via cyclic GMP, causes vasodilation of the arterioles. This increases blood flow through the corpora cavernosa which then expands producing an erection. Pheromones secreted by the female can stimulate the odour detecting system in the nasal cavity of the male (Chapter 12 and see above). Stress, however, activates the sympathetic system releases cyclic AMP which can result in vasoconstriction of the arterioles. Other factors that can interfere with an erection are physical fatigue and alcohol.

The physiology of penile erection involves an interplay of anatomical, hemodynamic, neurophysiological, and sex hormone interaction. Penile erection is the result of a complex interaction between the central nervous system and other local factors. This physical event also can be influenced by psychological factors. 

A normal penile erection requires the full functioning of several physiologic systems vascular, nervous, and hormonal. The patient must also be psychologically receptive to sexual stimuli. 

Stimulation of ai-adrenoreceptors will likely lead to detumescense, whereas blockade of these receptors, centrally and peripherally, including penile tissue, may produce erection. Female sexual arousal has been associated with an active sympathetic nervous system, but the overall data concerning the role of various neurotransmitters in female sexual function are still scanty. 

These often involve regulation of transcription. As mentioned in Chapter 18, Section F,2, many of the effects of NO are a resulf of activation of soluble gua-nylate cyclase (p. 561). In the endothelium other hormones, such as the endothelins (p. 1750), atrial natriuretic factor, and bradykinin (Box 22-D), cooperate in the regulation of NO synthase. Neuronal NO synthase fimctions in the brain in olfaction and in formation of memory. In the peripheral system it mediates penile erection and plays a variety of roles in the enteric nervous system. Neuronal NO synthase is often localized to synaptic regions by binding to tissue-specific proteins. NO may also regulafe cellular respiration by inhibition of cytochrome c oxidase. ... 

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