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The autonomic nervous system (ANS) is the major involuntary, unconscious, automatic portion of the nervous system and contrasts in several ways with the somatic (voluntary) nervous system. The anatomy, neurotransmitter chemistry, receptor characteristics, and functional integration of the ANS are discussed in this chapter. Major autonomic drug groups are discussed in Chapters 7, 8, 9, and 10. Drugs in many other groups have significant autonomic effects, many of which are undesirable.
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The motor (efferent) portion of the ANS is the major pathway for information transmission from the central nervous system (CNS) to the involuntary effector tissues (smooth muscle, cardiac muscle, and exocrine glands; Figure 6–1). Its 2 major subdivisions are the parasympathetic ANS (PANS) and the sympathetic ANS (SANS). The enteric nervous system (ENS) is a semiautonomous part of the ANS located in the gastrointestinal tract, with specific functions for the control of this organ system. The ENS consists of the myenteric plexus (plexus of Auerbach) and the submucous plexus (plexus of Meissner); these neurons send sensory input to the parasympathetic and sympathetic nervous systems and receive motor output from them.
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