1. Origin in the Brainstem
Nuclei:
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The vagus nerve fibers arise primarily from two major nuclei in the medulla oblongata:
- Dorsal motor nucleus of the vagus (parasympathetic component)
- Nucleus ambiguus (motor fibers to certain skeletal muscles, e.g., pharynx and larynx)
- Sensory information projects into the solitary nucleus (especially visceral and taste sensation).
Emergence from the Medulla:
- The vagus nerve exits the medulla on its lateral aspect, in the region between the olive and the inferior cerebellar peduncle.
- It exits the skull via the jugular foramen alongside the glossopharyngeal nerve (CN IX) and the accessory nerve (CN XI).
2. Ganglia Near the Jugular Foramen
- Superior (Jugular) Ganglion: Primarily for general somatic afferent fibers (skin of the ear, external auditory canal, etc.).
- Inferior (Nodose) Ganglion: Main visceral sensory ganglion carrying information from thoracic and abdominal viscera, as well as some taste fibers.
3. Cervical Course
Carotid Sheath:
In the neck, the vagus nerve descends within the carotid sheath posterior to and between the internal jugular vein and the common carotid artery (and further down, the internal carotid in the upper neck).
Major Branches in the Neck:
- Pharyngeal Branches: Contribute to the pharyngeal plexus (motor innervation to most pharyngeal muscles).
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Superior Laryngeal Nerve: Divides into:
- Internal laryngeal nerve: Sensory to the larynx above the vocal folds.
- External laryngeal nerve: Motor to the cricothyroid muscle.
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Recurrent Laryngeal Nerves:
- Right Recurrent Laryngeal Nerve: Loops around the right subclavian artery.
- Left Recurrent Laryngeal Nerve: Loops under the aortic arch near the ligamentum arteriosum.
- Both ascend in the neck to innervate all intrinsic muscles of the larynx except the cricothyroid.
4. Thoracic Course
Descending Through the Superior Mediastinum:
Both right and left vagus nerves enter the thorax posterior to the sternoclavicular joints or first rib.
Cardiac and Pulmonary Branches:
- Cardiac Branches: Form the cardiac plexus, providing parasympathetic innervation to the heart (slows heart rate and decreases force of contraction).
- Pulmonary Branches: Form the pulmonary plexuses around the bronchi, regulating bronchoconstriction and secretory activity in the lungs.
Esophageal Plexus:
The right and left vagus nerves approach the esophagus and form a network (the esophageal plexus) which gives rise to:
- Anterior Vagal Trunk: Primarily from the left vagus.
- Posterior Vagal Trunk: Primarily from the right vagus.
5. Abdominal Course and Termination
Passage Through the Diaphragm:
The anterior and posterior vagal trunks descend through the esophageal hiatus (an opening in the diaphragm at approximately the T10 vertebral level).
Parasympathetic Innervation in the Abdomen:
- Stomach: Regulates gastric secretions and motility.
- Small Intestine and Large Intestine (proximal colon): Provides parasympathetic supply generally as far as the splenic flexure of the colon.
- Other Branches: Some fibers supply the liver, gallbladder, pancreas, kidneys, and upper ureters via branches that accompany major abdominal arteries and autonomic plexuses (e.g., the celiac plexus).
Termination:
The vagus nerve “terminates” functionally by distributing its parasympathetic fibers extensively through the abdominal viscera up to about the splenic flexure of the large intestine. Beyond that, parasympathetic innervation is carried by the pelvic splanchnic nerves (S2–S4).
Key Points of the Vagus Nerve Pathway
- Origin: Medulla oblongata (dorsal motor nucleus, nucleus ambiguus).
- Skull Exit: Jugular foramen.
- Neck Course: Descends in the carotid sheath with the internal jugular vein and carotid artery; branches include pharyngeal, superior laryngeal, and recurrent laryngeal nerves.
- Thorax: Gives off cardiac, pulmonary, and esophageal branches, then forms the esophageal plexus.
- Abdomen: Becomes anterior and posterior vagal trunks, passes through the diaphragm, and innervates the stomach, intestines (to about the splenic flexure), liver, and other upper abdominal organs.
The wide-reaching distribution of the vagus nerve is why it is often called the “wanderer” (from Latin vagari, meaning “to wander”).