6.5.2. Parasympathetic Nerve Fibres: Pulmonary Branches and RLNs

Pulmonary Branches

These branches leave the main vagus nerve as it passes posterior to the root of the lung in the thorax. These branches form the pulmonary plexus, which is simply a network of nerves that sits on the anterior aspect of the primary bronchus and wrapped around the pulmonary veins. Again, the preganglionic fibres synapse in the plexus and continue as postganglionic fibres, which will innervate the bronchi; in fact, they will constrict the bronchi when stimulated. This applies to the left and right vagus nerves.

Recurrent Laryngeal Nerves

This branch innervates the larynx in the neck but it is worth considering it briefly here. It's a strange nerve. It branches off the main vagus nerve and turns 180o and ascends up to the larynx. The left and right vagus nerves give off this branch at slightly different locations. The right recurrent laryngeal nerve branches off the right vagus nerve at the level of the subclavian artery. It then curves under the subclavian artery and travels all the way up to the larynx. The left recurrent laryngeal nerve branches off the left vagus nerve further down, at the level of the aortic arch. It then sweeps under the aortic arch and ascends to the larynx. Both recurrent laryngeal nerves carry sensory information from the larynx and motor fibres to almost all of the intrinsic muscles of the larynx. However, here we are only considering the function of the parasympathetic fibres of the vagus nerve - the parasympathetic fibres are not responsible for the somatic sensory and motor actions in the larynx. Actually, these somatic actions are due to the fact that the vagus nerve carries some somatic fibres as well as parasympathetic fibres. The parasympathetic fibres are only responsible for the innervation of some of the glands of the larynx and trachea (via the recurrent laryngeal nerve).