The glossopharyngeal nerve belongs to the cranial nerves and has six branches in which it carries motor, parasympathetic, sensory and sensitive fibers. With them, the glossopharyngeal nerve predominantly innervates the pharynx, tongue, and palatine tonsil.
What is the glossopharyngeal nerve?
Twelve cranial nerves exit the brain at different points in the head and increasingly branch to form a network of nerves that runs primarily through the head. The glossopharyngeal nerve corresponds to the ninth cranial nerve and is also known as the lingual pharyngeal nerve because of its functions. Unlike other nerve pathways, the cranial nerves do not pass through the spinal cord. In addition, the glossopharyngeal nerve belongs to the subgroup of gill arch nerves because it forms from the third gill arch during embryonic development. Five other gill arches give rise to the trigeminal nerve, the facial nerve, and the vagus nerve. Medicine alternatively refers to gill arch nerves as brachial nerves – the visceromotor control of the glossopharyngeal nerve is accordingly known as brachiomotor function.
Anatomy and structure
The glossopharyngeal nerve has six major branches:
- Tympanic nerve
- Rami tonsillares
- Ramus sinus carotici
- Ramus pharyngeus
- Ramus musculi stylopharyngei
- Rami linguales
The tympanic nerve or tympanic cavity nerve leads to the middle ear, where its sensory fibers contribute to the tympanic plexus. The plexus is located in the tympanic cavity and also contains fibers of the caroticotympanic nerve. Between the tympanic plexus and the otic ganglion, the petrosal minor nerve forms a connection. It is also known as Jacobson’s anastomosis. In addition, the glossopharyngeal nerve reaches the otic ganglion via the tonsillar branches or rami tonsillares. Furthermore, the carotid branch (ramus sinus carotici) branches off from the lingual pharyngeal nerve. It forms on the one hand the glomus caroticum at the carotid artery (Arteria carotis communis) and on the other hand the sinus caroticus at the internal carotid artery (Arteria carotis interna). The pharyngeal branch (ramus pharyngeus) of the glossopharyngeal nerve leads to the pharyngeal plexus, where it intermingles with fibers from the tenth cranial nerve (vagus nerve), the laryngeal nerve (superior laryngeal nerve), and the superior cervical ganglion (superior cervical ganglion). The ramus musculi stylopharyngei innervates one of the pharyngeal elevators (stylopharyngeus muscle). Finally, the rami lingualis form a group of branches of the glossopharyngeal nerve. They represent the terminal branch and supply the posterior part of the tongue.
Function and tasks
The various branches of the glossopharyngeal nerve contain motor as well as sensory, sensory, and parasympathetic fibers. The motor portions are predominantly visceromotor neurons and are not subject to conscious human control. The ramus musculi stylopharyngei is an exception, as the pharyngeal elevator is a striated muscle and belongs to the skeletal musculature. It participates in swallowing, working in conjunction with the other pharyngeal, palatine, and lingual muscles. In the tympanic nerve, which passes over the tympanic plexus, the glossopharyngeal nerve uses sensitive fibers to transmit sensations such as pressure, pain, touch, vibration, and temperature in the middle ear. The otic ganglion, to which the tympanic plexus is connected, also regulates salivary glands. With the help of parasympathetic fibers, the glossopharyngeal nerve further contributes to the autonomic nervous system. The glomus caroticum and the sinus caroticus monitor the common carotid artery and the internal carotid artery. The glomus caroticum transmits information to the brain about pH, oxygen, and carbon dioxide in the blood, while the carotid sinus measures blood pressure. In the medulla oblongata (]]medulla oblongata]]), the respiratory center and the circulatory center trigger adaptations when needed and, for example, increases the respiratory rate. In addition, the glossopharyngeal nerve plays a role in tasting, supplying the posterior region of the tongue with sensory nerve fibers. In its oral mucosa are taste buds in which chemical receptors are located. The posterior third of the tongue accounts for half of gustatory perceptions.
Diseases
Damage to the glossopharyngeal nerve can cause dysphagia, in which food or liquid enters the nose. The problem is primarily caused by failure of the pharyngeal plexus and additional paralysis of the stylopharyngeus muscle. In addition, with complete failure of the glossopharyngeal nerve, ageusia typically occurs: Affected individuals can no longer perceive any of the taste qualities in the posterior third of the tongue. However, swallowing and tasting disorders can also occur in association with other neurological diseases and syndromes and do not always indicate a lesion of the glossopharyngeal nerve. Glossopharyngeal palsy is often accompanied by paralysis of the vagus nerve; the accessorius nerve may also be affected. This is often due to skull injuries, poisoning, and neurological disorders such as strokes and various forms of dementia. Pharyngismus is a spasm of the pharynx due to continued action potentials in the glossopharyngeal nerve and occurs in severe infectious diseases such as rabies or tetanus. Therefore, medicine knows this condition as glossopharyngeal spasm. Neuralgic pain of the palate and pharynx is also due to the tongue-throat nerve in some cases and may radiate to the tongue, throat, jaw, and ear. The symptoms occur mainly during speaking, swallowing, chewing or yawning and are sometimes accompanied by taste disturbances, an increase in saliva production and numbness in the affected area. The clinical picture is also known as Collet-Sicard syndrome and arises idiopathically or secondarily due to neuritis, scars, or tumors.
