What is the nerve supply of thyropharynx and cricopharynx?
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Nerve Supply of Thyropharyngeus and Cricopharyngeus
The inferior pharyngeal constrictor has two parts - the thyropharyngeus (upper part, arising from the oblique line of the thyroid cartilage) and the cricopharyngeus (lower part, arising from the cricoid cartilage). Their nerve supplies differ slightly:
Thyropharyngeus
- Pharyngeal plexus - the primary motor supply
- Motor fibres originate in the cranial root of the accessory nerve (CN XI) and are carried by the pharyngeal branch of the vagus nerve (CN X)
- The plexus also receives contributions from the glossopharyngeal nerve (CN IX) and sympathetic branches of the superior cervical ganglion
- The plexus is a meshwork on the posterolateral surface of the pharynx; nerve fibres descend over the external surface of the pharyngeal constrictors to reach the deeper muscle layers
Cricopharyngeus
The cricopharyngeus has a richer and more varied innervation than the rest of the inferior constrictor:
- Pharyngeal plexus (same as above - CN X carrying CN XI fibres, CN IX, sympathetics)
- External laryngeal nerve (branch of the superior laryngeal nerve from CN X)
- Recurrent laryngeal nerve (branch of CN X) - this is the key distinguishing feature; the cricopharyngeus is the only part of the pharyngeal constrictors to receive direct recurrent laryngeal nerve branches
This dual innervation is clinically significant: the cricopharyngeus acts as the upper oesophageal sphincter, and its unique nerve supply (especially the recurrent laryngeal nerve component) explains why recurrent laryngeal nerve palsy can affect swallowing and why cricopharyngeal dysfunction is implicated in Zenker's diverticulum formation at Killian's dehiscence (the weak area between thyropharyngeus and cricopharyngeus).
Summary Table
| Muscle | Pharyngeal Plexus (CN X + XI) | External Laryngeal N. | Recurrent Laryngeal N. |
|---|---|---|---|
| Thyropharyngeus | Yes | No | No |
| Cricopharyngeus | Yes | Yes | Yes |
Sources: Scott-Brown's Otorhinolaryngology Head & Neck Surgery (Pharyngeal Plexus of Nerves section); Cummings Otolaryngology Head and Neck Surgery (Anatomy of the Hypopharynx and Cervical Esophagus)
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