The Autonomic Nervous System Has Two Major Subdivisions
The ANS is divided into two major subdivisions based on the anatomical origin of their preganglionic neurons and on their synaptic transmitters at the target organ. These two subdivisions are the sympathetic nervous system and the parasympathetic nervous system.
FIGURE 13-1 The autonomic nervous system (ANS) differs from the somatic motor system in the number of neurons that it has in the peripheral nervous system.The somatic motor system has one neuron, whose cell body is located in the central nervous system (CNS) and whose axon extends, uninterrupted, to the skeletal muscle, where the peripheral chemical synapse occurs.
In contrast, the ANS has two neurons in the path from the CNS to the target. The first, called a preganglionic neuron, also has its cell body in the CNS, but its axon innervates a second neuron in the chain, called the postganglionic neuron. Its cell body is in a peripheral structure called a ganglion.
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