Pharyngeal plexus

The pharyngeal plexus lies on the posterolateral wall of the pharynx, mainly over the middle pharyngeal constrictor and is the main motor and sensory nerve supply to the muscles of the pharynx and soft palate and acts to coordinate swallowing and speech .

Summary

• location: within the external fascia of the pharynx , mainly over the middle pharyngeal constrictor on the posterolateral wall of the pharynx.
• origin and course: it is formed from the union of branches from the vagus nerve, glossopharyngeal nerve and cervical sympathetic nerves .
• branches and supply: filaments from the plexus ascend or descend external to the superior and inferior constrictors before branching within the muscular layer and mucosa of the pharynx . It supplies the superior, middle and inferior pharyngeal constrictor muscles, palatopharyngeus, salpingopharyngeus, levator veli palatini, palatoglossus and the muscle of the uvula .
• relations: the pharyngeal plexus lies in the retropharyngeal space between the superior and middle constrictor muscles anteriorly and the longus capitus and colli muscles, prevertebral fascia, and bodies of the second and third cervical vertebrae posteriorly and medial to the buccopharyngeal fascia.

Gross anatomy

The pharyngeal plexus lies within the external fascia of the pharynx on the posterolateral wall of the pharynx in the retropharyngeal space . It lies mainly over the middle pharyngeal constrictor muscle although it spreads its branches over the dorsolateral surface of the both the superior and middle constrictors, and lower branches descend onto the inferior constrictor . The pharyngeal plexus sends some branches between the middle and inferior constrictors and other branches between the superior and middle constrictors . It is formed by the pharyngeal branches from the vagus and glossopharyngeal nerves and the cervical sympathetic .

The pharyngeal branch of the glossopharyngeal nerve arises prior to the glossopharyngeal nerve curving around the posterior border and lateral side of the stylopharyngeus . It joins the pharyngeal branch of the vagus nerve which proceeds to join the pharyngeal plexus and pierce the middle constrictor muscle . This component is afferent and supplies the mucous membrane of the oropharynx with common sensation and some taste fibers . Parasympathetic fibers from the inferior salivary nucleus are also supplied to the mucous and serous glands of the oropharynx via the pharyngeal branches of the glossopharyngeal nerve .

The pharyngeal branch of the vagus emerges from the upper part of the inferior vagal ganglion and passes forward between the internal and external carotid arteries parallel with and below the glossopharyngeal nerve to join the pharyngeal plexus at the upper border of the middle pharyngeal constrictor muscle . It contains motor fibers originating from the nucleus ambiguus in the medulla as well as afferents originating in the sensory nucleus of the trigeminal nerve . Motor fibers of the pharyngeal branch of the vagus originating from the cranial part of the accessory nerve are described as acting as the major motor drive to the pharyngeal plexus . Although, recently, discussion regarding the accessory nerve’s contribution has arisen on the basis of connections between the accessory nerve and vagus nerve in the posterior fossa being variable . The vagal contribution to the pharyngeal plexus supplies the muscles of the pharynx except (stylopharyngeus) and the muscles of the soft palate (except tensor veli palatini) .

Sympathetic fibers are supplied from the superior cervical ganglion via branches from the plexus on the external carotid artery; this element is vasoconstrictor .

The superior, middle and lower pharyngeal constrictor muscles, palatopharyngeus, salpingopharyngeus, levator veli palatini, palatoglossus and the muscle of the uvula are all innervated by branches of the pharyngeal plexus  . The innervations of levator veli palatini and uvular muscle remain controversial . The levator veli palatini muscle has been reported by varying sources to receive its nerve supply solely through the pharyngeal plexus or doubly through the pharyngeal plexus and branches of the facial nerve . The muscle of the uvula has been reported to receive both dual innervation from the pharyngeal plexus and lesser palatine nerve, and also sole innervation from either nerve . No consensus currently exists.

Related pathology

Lesions may cause dysfunction of the pharyngeal plexus at various levels of the nervous system, including supranuclear, brain stem, peripheral nerve and neuromuscular junction . Unilateral right sided pharyngeal plexus injury has been reported following use of an orophryngeal pack during third molar surgery in which the patient exhibited sensory loss over the right side of the pharynx, soft palate, and posterior third of the tongue and weakness of the right side of the pharynx and soft palate without vocal cord injury . A case of isolated transient pharyngeal plexus injury has been reported following posterior plating of a C2 fracture in which the patient presented with dense pharyngeal paralysis and inability to initiate swallowing but with true vocal cord movement preserved.