Point
8
Intro
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READ ON ONLY IF YOU ARE INTERESTED. I WILL NOT, REPEAT, WILL NOT ASK YOU ANY QUESTIONS ABOUT WHAT FOLLOWS. |
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Preganglionic parasympathetic visceromotor fibers from the vagus also activate postganglionic neurons in ganglia associated with the lungs (pulmonary and bronchial plexuses). These postganglionic fibers innervate smooth muscle and glands of bronchioli. Stimulation of the dorsal motor nucleus results in constriction of the smooth muscle of bronchioli and increased secretion from the bronchial glands. There is mixing of the right and left vagi in the pulmonary plexuses, so a unilateral lesion of one dorsal motor X will be "covered" by the other nucleus and nerve. The visceromotor fibers from the vagus that reach the stomach and gut end in postganglionic neurons that lie near (gastric plexus) or in (myenteric and submucosal plexuses) the organs. Stimulation of the dorsal motor nucleus results in increased peristalsis and secretion of gastric and intestinal juices, and relaxation of sphincters. You might remember from Gross Anatomy that the right and left vagus nerves exchange fibers on the outer surface of the esophagus. They then enter the abdomen as anterior (or ventral) and posterior (or dorsal) vagal trunks. There is considerable mixing of the right and left vagi as they innervate the stomach and intestine. Afferent sources (inputs) to the dorsal motor nucleus include the hypothalamus, olfactory system, autonomic centers in the reticular formation, and especially the nucleus solitarius. Most of these afferent sources you have never heard of. So, right now remember that the dorsal motor nucleus X plays an important role in various visceral reflexes. Thus, information about the "internal milieu" reaches the dorsal motor nucleus of X via visceral afferent pathways that we will soon talk about. The dorsal motor nucleus X receives these afferent messages and then sends information to the appropriate organ(s) (via the terminal ganglia). |