Autonomic Fibers

NUCLEUS

The dorsal vagal motor nucleus is the origin of the preganglionic, parasympathetic fibers (general visceral efferent) of the vagus nerve. This nucleus is a column of cells located in the floor of the fourth ventricle medial to the nucleus ambiguus. These parasympathetic fibers of the vagus control secretion of glands in the mucosa of the larynx, pharynx, gut from the esophagus to the colon at the splenic flexure, pancreas, liver, and lungs. Fibers to the stomach are responsible for acid secretion. Activation of the parasympathetic fibers to the heart results in slowing of the heart rate; such activation also produces a negative inotropic effect on heart muscle contraction. The vagus parasympathetic fibers also innervate smooth muscle of the airway and gut. These fibers carry signals to open the airway during breathing, to produce bronchoconstriction, and also to coordinate peristalsis of the esophagus and intestine.

SUPRANUCLEAR CONTROL

The dorsal motor nucleus of the vagus receives input from the hypothalamus, the nucleus of the tractus solitarius, the reticular formation, and the olfactory system. PERIPHERAL PATHWAYS

The parasympathetic fibers affect numerous body functions in structures within the neck, thorax, and abdomen. They leave the cranium with the vagus nerve through the jugular foramen. These preganglionic fibers terminate near their target sites on ganglia associated with plexuses at several locations, including the esophagus, pharynx, lungs, heart, and intestines. The parasympathetic functions of the vagus nerve are addressed in the chapter on the autonomic nervous system.

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