AUTONOMIC NERVOUS SYSTEMThe autonomic nervous system (ANS) is theportion of the PNS that functions independently,automatically, and continuously, without consciouseffort. It helps to regulate the smooth muscles, cardiacmuscle, digestive tube, blood vessels, sweat anddigestive glands, and certain endocrine glands. Theautonomic nervous system is not directly under thecontrol of the brain but usually works in harmony withthe nerves that are under the brain's control. Theautonomic nervous system includes two subdivisions(the sympathetic and parasympathetic nervoussystems) that act together.The sympathetic nervous system's primaryconcern is to prepare the body for energy-expending,stressful, or emergency situations. On the other hand,the parasympathetic nervous system is most activeunder routine, restful situations. The parasympatheticsystem also counterbalances the effects of thesympathetic system, and restores the body to a resting1-40HM3F0146C1C2C3C4C5C6C7C8T1T2T3T4T5T6T7T8T9L1L2L3L4L5S1S2S3S4S5CoT10T11T12POSTERIORVIEWCERVICALNERVESTHORACICNERVESLUMBARNERVESSACRALNERVESCOCCYGEALNERVEFigure 1-46.—Spinal nerves.
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