Anterior Vagus Nerve/vagus nerve is thus named because it follows a complex course throughout the body to innervate several organs; fibers originate from the dorsal motor nucleus and nucleus ambiguus in the ventral medulla oblongata of the brainstem, with terminal branches reaching the splenic flexure of the colon. A critical division during the nerve’s course from rostral to caudal occurs as it enters the abdominal cavity: it splits into an anterior trunk and a posterior trunk. The structural and functional properties of the anterior trunk, along with its relevant surgical and clinical considerations, will be examined in this article.[rx][rx][rx]
Structure and Function
Four nuclei located at varying levels of the medulla house cell bodies of the vagus nerve: the dorsal nucleus, which serves parasympathetic function to the heart, lungs, and gastrointestinal tract via general visceral efferent fibers; the nucleus ambiguus, which is responsible for special visceral efferent activity and houses cell bodies not only for the vagus nerve, but also for the ninth and eleventh cranial nerves; the solitary nucleus, which receives general visceral afferent innervation from the carotid body and sinus via cranial nerve nine, general visceral afferent information from the aortic bodies and sinoatrial node of the heart, as well as special visceral afferent information (i.e., taste) from the anterior two-thirds of the tongue.[rx]
The vagus nerve proper is formed from multiple rootlets as it emerges from the cranial vault through the jugular foramen. After its emergence, two sensory ganglia form: these are the superior ganglion and inferior ganglion. These ganglia house the cell bodies of the sensory neurons responsible for the vagus nerve’s afferent activity.[rx]
As the vagus nerve enters the abdominal cavity through the esophageal hiatus, it splits into an anterior trunk and a posterior trunk. The anterior trunk is mainly responsible for gastrointestinal parasympathetic innervation to the lesser curvature of the stomach, the pylorus, the biliary apparatus, and the gallbladder.
Blood Supply and Lymphatics
An explicit artery, the vagal artery, provides the primary blood supply to the vagus nerve. This artery tracks on the anterior surface of the nerve and is at considerable risk during several surgical procedures.[rx]
The bronchoesophageal artery supplies the vagus nerve with a branch in the mediastinum, to the left in the subaortic region. Additionally, in the mediastinal region, the vagus nerve can be vascularized by arteries from the aortic arch, from a first intercostal artery, and inferior thyroid artery.
The veins that affect the vagus nerve at the level of the mediastinum are the internal thoracic vein from the anterior area and the thoracic intercostal veins from the posterior area.
Nerves
Important branches of the vagus nerve include: the superior laryngeal nerve, which has two branches, the internal laryngeal nerve (at risk with regional lymphadenopathy or trauma), and the external laryngeal nerve (at risk during superior thyroid artery ligation); and the recurrent laryngeal nerve (at risk as it wraps around the aortic arch on the left-handed side; therefore, aortic arch pathology, such as an aneurysm of any kind, endangers this nerve. It can also be damaged during patent ductus arteriosus repair, as well as perioperatively during ligation of the nearby inferior thyroid artery.[rx][rx]
The vagus nerve splits into two trunks: the anterior and posterior vagal trunks. The anterior trunk, which receives significant contributions from the left vagus nerve more so than the right, branches into: a hepatic branch, which supplies the liver, gallbladder, and biliary apparatus; a celiac branch, which contributes parasympathetic fibers to the celiac plexus; and numerous anterior gastric branches, the most medial of which courses along the lesser curvature of the stomach. The pylorus and proximal duodenum receive innervation from the anterior and posterior nerves of Latarjet, which are both branches off of the anterior vagal trunk.[rx]
Muscles
Several muscles receive innervation from the vagus nerve: the middle and inferior pharyngeal constrictor muscles, which are responsible for passage of food boluses; the palatoglossus, which elevates the posterior portion of the tongue on swallowing; and the laryngeal muscles, the aryepiglottic, thyroarytenoid, arytenoid, lateral and posterior cricoarytenoid, which are innervated by the recurrent laryngeal nerve. The entire length of the esophagus is also the recipient of motor innervation.[rx]
The vagus nerve innervates the crural area of the diaphragm (where the esophagus passes or esophageal hiatus).
The tenth cranial nerve innervates the suspensory muscle of the duodenum or musculus suspensorius duodeni.
References
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