The parasympathetic and sympathetic divisions are antagonistic to one another and organs under the influence of the ANS have dual innervation. Typically, one division either inhibits the organ from functioning or causes an increase in activity in the organ. This occurs due to the difference in neurotransmitters secreted by the separate divisions. At the terminal end of the parasympathetic division, the neurotransmitter is acetylcholine. At the terminal end of the sympathetic division, the neurotransmitter is mostly norepinephrine.
The neurons leaving the CNS are called preganglionic neurons. In the case of the parasympathetic division, the preganglionic neurons secrete acetylcholine as neurotransmitters. The ganglia of the parasympathetic division are next to, or in, the organ they innervate. The postganglionic neurons secrete acetylcholine as well. In the sympathetic division, the preganglionic neurons secrete acetylcholine in the sympathetic chain ganglia. The postganglionic neurons mostly secrete norepinephrine to stimulate or inhibit the organs they innervate.
Answer Key: a. Preganglionic, b. Postganglionic, c. Ganglia, d. Oculomotor III, e. Facial VII, f. Glossopharyngeal IX, g. Vagus X, h. S2, i. S4
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