This represents the component of the nervous system that is not under voluntary control, innervating the viscera, cardiac and smooth muscle and secretory glands. It helps maintain internal homeostasis, controlling the gastrointestinal and genito-urinary tracts and the cardiovascular and respiratory systems. It regulates visceral, endocrine, immune, behavioural, body temperature and pain functions. The stress response is largely due to autonomic activation. The autonomic nervous system consists of an afferent limb, central integrated elements and an efferent limb. It subserves the following specific functions: Control of smooth muscle activity in blood vessels and viscera; Innervation of muscle fibres in the heart and in the uterus; Control of secretion from salivary, mucus-secreting and eccrine sweat glands; Activity of the adrenal medulla;
Digestive and metabolic activity of the liver, gastrointestinal tract and the pancreas;
Transmission of visceral pain and organic visceral sensation, e.g. hunger, bladder and bowel fullness, nausea; Motility of the gastrointestinal tract; Sexual responses of the genitalia and reproductive organs. In general, sympathetic and parasympathetic systems produce opposing effects on most viscera. In a few viscera they exert synergistic effects.
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