Anatomy of motor component

The motor component of the vagus nerve has both parasympathetic and general motor functions.

The parasympathetic part of the vagus nerve arises from cell bodies in the dorsal motor nucleus in the floor of the fourth ventricle posterolateral to the hypoglossal nucleus. Nerve fibres emerge from the brainstem in 8-10 rootlets which pass through the jugular foramen and pass down the neck in the carotid sheath. The preganglionic fibres go on to innervate ganglia in the walls of target viscera, postganglionic fibres then going on to supply glands and smooth muscle in target organs:

• the bronchial tree: secretions and bronchoconstriction
• the heart: the SAN and AVN to cause bradycardia
• the gastrointestinal tract: secretions, e.g. enzymes, and peristaltic contractions

The general motor function of the vagus nerve relates to its innervation of muscles in the palate, pharynx and larynx. The origin of these fibres is the nucleus ambiguus deep in the reticular formation of the medulla. The rostral fibres of this nucleus pass to join the vagus nerve at the jugular foramen. The pharyngeal plexus is given off soon after to supply the majority of muscles in the palate and pharynx.

Some motor nerve fibres continue within the carotid sheath to form the recurrent laryngeal nerves. On the left the fibres bend around the aorta, on the right, the subclavian artery. They ascend again between the oesophagus and the trachea to innervate the intrinsic muscles of the larynx, including the vocal folds.