Motor Fibers Nucleus

The nucleus ambiguus is the origin of special visceral efferent fibers of the vagus nerve, which supply striated muscles of the tongue and larynx, and all of the striated muscles of the soft palate and the pharynx except for the tensor veli palatini and the stylopharyngeus (which are innervated by branches of cranial nerves V and IX, respectively) (see Table 13-1 ). The palatoglossus is the only tongue muscle supplied by the vagus nerve; the remainder are supplied by cranial nerve XII. The palatoglossus muscle originates in the soft palate and passes through the tongue in a transverse fashion. Together with the styloglossus muscle, it acts to elevate the posterior tongue.


The nucleus ambiguus receives input from motor areas of the cerebral cortex, particularly the precentral gyrus. The cortical input is bilateral and indirect. The corticobulbar fibers terminate first on adjacent reticular formation fibers, which in turn transmit signals to the nucleus ambiguus. The nucleus also receives sensory input from the larynx, pharynx, and airways, which mediate reflexive actions such as coughing, swallowing, and vomiting.


The special visceral efferent fibers exit the skull through the jugular foramen with the vagus nerve and then divide into three major branches: the pharyngeal nerve, superior laryngeal nerve, and recurrent laryngeal nerve. The pharyngeal

Figure 13-2 Diagram of the vagus nerve (cranial nerve X), specifically, its branch, the recurrent laryngeal nerve, and its relationship to the large vessels of the neck. The right and left nerves are not identical, and the recurrent laryngeal nerve branches at the base of the neck on the right and in the thorax on the left.

and superior laryngeal nerves branch from the vagus high in the neck. The recurrent laryngeal nerve branches at the base of the neck on the right and in the thorax on the left ( Fig 13-2 ). The pharyngeal nerve enters the pharynx and divides into the pharyngeal plexus to supply the muscles noted earlier. The superior laryngeal nerve descends and divides to reach the cricothyroid and the inferior constrictor muscles. The right and left recurrent laryngeal nerves take different paths to reach their destination, supplying all of the intrinsic muscles of the larynx except the cricothyroid. On the right, the recurrent laryngeal nerve descends anterior to the subclavian artery, loops posteriorly beneath it, and then turns upward again, running along the right side of the trachea to the larynx. The left recurrent laryngeal nerve passes under the aortic arch and travels upward in a groove between the left trachea and esophagus to the larynx.

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