OverviewThe parasympathetic (secretomotor) component of the vagus nerve consists of efferent fibers which innervate the smooth muscle and glands of the pharynx, larynx, and thoracic and abdominal viscera down to the splenic flexure.
In general, parasympathetic stimulation leads to increased secretion from glands and smooth muscle contraction. Specifically, CN X parasympathetic stimulation has the following effects (think "rest and digest"):
- Cardiac - Slows heart rate
- Lungs - Stimulates increased bronchiolar secretions and bronchoconstriction
- GI tract- Stimulates increased secretions and motility
Origin and Central Course
The visceral motor component fibers originate from the dorsal motor nucleus of the vagus located in the floor of the fourth ventricle (vagal trigone) in the rostral medulla and in the central grey matter of the closed (caudal) medulla.
Preganglionic fibers course through the spinal trigeminal tract and nucleus to exit the lateral medulla.
Upon emerging from the lateral aspect of the medulla, the visceral motor fibers join the other components of CN X to exit the skull via the jugular foramen.
Extra-Cranial Course and Final Innervations
Upon exiting the skull the vagus nerve travels between the internal jugular vein and internal carotid artery within the carotid sheath.
Preganglionic fibers to the secretomotor glands of the pharyngeal and laryngeal mucosa travel with the pharyngeal and internal laryngeal nerves discussed above.
Within the thorax the left and right vagus nerves break up into many branches to form plexuses around the esophagus and major blood vessels to the heart and lungs.
From the esophageal plexus, the left and right gastric nerves emerge and provide preganglionic parasympathetic innervation to the stomach.
Innervation to the intestines and visceral organs generally follow the arterial blood supply to that organ.