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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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AdrenergicA nerve ending that releases norepinephrine as the primary transmitter; also, a synapse in which norepinephrine is the primary transmitter
Adrenoceptor, adrenergic receptorA receptor that binds, and is activated by, one of the catecholamine transmitters or hormones (norepinephrine, epinephrine, dopamine) and related drugs
Baroreceptor reflexThe neuronal homeostatic mechanism that maintains a constant arterial blood pressure; the sensory limb originates in the baroreceptors of the carotid sinus and aortic arch; efferent pathways run in parasympathetic and sympathetic nerves
CholinergicA nerve ending that releases acetylcholine; also, a synapse in which the primary transmitter is acetylcholine
Cholinoceptor, cholinergic receptorA receptor that binds, and is activated by, acetylcholine and related drugs
DopaminergicA nerve ending that releases dopamine as the primary transmitter; also a synapse in which dopamine is the primary transmitter
Homeostatic reflexA compensatory mechanism for maintaining a body function at a predetermined level, for example, the baroreceptor reflex for blood pressure
Nonadrenergic, noncholinergic (NANC) systemNerve fibers associated with autonomic nerves that release purines or peptides, not norepinephrine or acetylcholine
ParasympatheticThe part of the autonomic nervous system that originates in the cranial nerves and sacral part of the spinal cord; the craniosacral autonomic system
Postsynaptic receptorA receptor located on the distal side of a synapse, for example, on a postganglionic neuron or an autonomic effector cell
Presynaptic receptorA receptor located on the nerve ending from which the transmitter is released into the synapse; modulates the release of transmitter
SympatheticThe part of the autonomic nervous system that originates in the thoracic and lumbar parts of the spinal cord

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.

Figure 6–1

Schematic diagram comparing some features of the parasympathetic and ...

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