Concepts of Human Anatomy & Physiology   5/e   Van De Graaff/Fox
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Concept: The autonomic nervous system helps to regulate the activities of smooth muscle, cardiac muscle, and glands. In this regulation, impulses are conducted from the CNS by an axon that synapses with a second autonomic neuron. It is the axon of this second neuron in the pathway that innervates the involuntary effectors.

II. Divisions of the Autonomic Nervous System

Concept: Preganglionic neurons of the sympathetic division of the autonomic nervous system originate at the thoracic and lumbar levels of the spinal cord and send axons to sympathetic ganglia, which parallel the spinal cord. Preganglionic neurons of the parasympathetic division, by contrast, originate in the brain and in the sacral level of the spinal cord and send axons to ganglia located in different regions in or near the effector organs.

III. Functions of the Autonomic Nervous System

Concept: The sympathetic division of the autonomic nervous system activates the body to "fight or flight," largely through the release of norepinephrine from postganglionic fibers and the secretion of epinephrine from the adrenal medulla. The parasympathetic division often produces antagonistic effects through the release of acetylcholine from its postganglionic fibers. The actions of both divisions of the autonomic nervous system must be balanced in order to maintain homeostasis.

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