Innervation of human soft palate muscles

Abstract

Our objective was to determine the branching and distribution of the motor nerves supplying the human soft palate muscles. Six adult specimens of the soft palate in continuity with the pharynx, larynx, and tongue were processed with Sihler's stain, a technique that can render large specimens transparent while counterstaining their nerves. The cranial nerves were identified and dissection followed their branches as they divided into smaller divisions toward their terminations in individual muscles. The results showed that both the glossopharyngeal (IX) and vagus (X) nerves have three distinct branches, superior, middle, and inferior. Only the middle branches of each nerve contributed to the pharyngeal plexus to which the facial nerve also contributed. The pharyngeal plexus was divided into two parts, a superior innervating the palatal and neighboring muscles and an inferior innervating pharyngeal constrictors. The superior branches of the IX and X nerves contributed innervation to the palatoglossus, whereas their middle branches innervated the palatopharyngeus. The palatoglossus and palatopharyngeus muscles appeared to be composed of at least two neuromuscular compartments. The lesser palatine nerve not only supplied the palatal mucosa and palatine glandular tissue but also innervated the musculus uvulae, palatopharyngeus, and levator veli palatine. The latter muscle also received its innervation from the superior branch of X nerve. The findings would be useful for better understanding the neural control of the soft palate and for developing novel neuromodulation therapies to treat certain upper airway disorders such as obstructive sleep apnea.

Morphometric and Immunohistochemical Characteristics of the Adult Human Soft Palate Muscles

“…30,31 Our recent study showed that human MU muscle is innervated by the LPN only. 2 This novel finding challenges the current and prevailing view that the LPN is a sensory nerve that innervates the palatal mucosa and palatine glandular tissue. 1 MU muscle is regarded as a velar elevator, stiffness modifier, and extensor.…”

“…22 Our study showed that the human LVP receives dural innervation from both the pharyngeal branch of the X nerve and LPN. 2 LVP is the primary muscle for velar elevation and velopharyngeal closure for speech production 23,24 and swallowing. 25 During swallowing and speech, velopharyngeal closure is achieved by the velum, lateral and posterior pharyngeal walls.…”

“…Our study demonstrated that PP receives triple innervation from the LPN and pharyngeal branches of the IX and X nerves. 2 The type II predominance in the PP indicates that it is a fast muscle for rapid phasic movements of the soft palate. Contraction of the PP depresses soft palate, elevates pharynx, and narrows fauces as seen during swallowing 37,38 and speech.…”

“…43 Our study demonstrated that the human PG is innervated by the pharyngeal branches of the IX and X nerves. 2 Contraction of the PG lowers soft palate, elevates posterior tongue, and constricts the anterior tonsillar pillars, as seen during swallowing 44 and speech. 45 During speech, PG contraction elevates the posterior tongue to produce oral constrictions, and lowers the velum to open the velopharyngeal port for the production of nasal phonemes.…”

“…Anatomically, soft palate is characterized by containing five pairs of palatal muscles, including the levator veli palatini (LVP), musculus uvulae (MU), palatopharyngeus (PP), palatoglossus (PG), and tensor veli palatini (TVP) 1 that intertwine in a complex fashion. Our recent studies 2 have demonstrated that the human soft palate muscles are innervated by multiple cranial nerves, including the pharyngeal branches of the glossopharyngeal (IX) and vagus (X) nerves as well as the lesser palatine nerve (LPN). Some palatal muscles receive dual or triple innervation.…”