6.5.1. Parasympathetic Nerve Fibres: Vagus Nerve
The Course of the Vagus Nerve
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The ‘centre’ in the brain associated with the vagus nerve is found in the medulla of the brainstem. This ‘centre’ is called the 'dorsal motor nucleus of the vagus'. The preganglionic motor fibres of the vagus nerve leave the nucleus and travel inferiorly through the base of the skull, down the neck in the carotid sheath. Here, it runs beside the common carotid artery and descends into the thorax. The vagus nerve descends posterior to the 'root of the lung'* and the heart. Eventually, it leaves the thorax along with the oesophagus, through the oesophageal hiatus, as a vagal trunk. The left vagus nerve gives rise to the anterior vagal trunk, and the right vagus nerve gives rise to the posterior vagal trunk. Remember earlier we said that the vagus nerve will provide nervous innervation in the abdomen too, all the way up to the transverse colon.
*What is the root of the lung? It is the point where all of the vessels and bronchi enter/leave the lung. It's also called the hilum of the lung.
But the Vagus Nerve Has Lots of Branches
However, while in the neck and upper thorax, the preganglionic fibres of the vagus nerve will give rise to a number of important branches:
(1) Pulmonary branches
(2) Recurrent laryngeal nerves
(3) Cardiac branches
Let's look at each of these in detail.