Motor system and common nucleus
Both nerves share a common motor nucleus — the nucleus ambiguus (nucleus ambiguus). The cranial part of the accessory nerve (XI pair) also joins it.
- Area of responsibility: striated muscles of the pharynx, larynx, soft palate, and upper third of the esophagus.
- Cortical regulation: the nucleus ambiguus receives descending commands from the lower parts of the precentral gyrus. A crucial feature is that innervation here is bilateral.
Due to this bilateral connection with the cortex, a unilateral lesion of the central pathways (e.g., in stroke) does not lead to critical impairment of swallowing or voice — the healthy half of the brain compensates for the deficit.
Sensory innervation and taste
The sensory fibers of both nerves originate from pseudounipolar cells located in the superior and inferior ganglia (in the area of the jugular foramen). Central processes travel to the nucleus of the solitary tract (nucleus tractus solitarii), and from there via the thalamus to the cortex.
Areas of general sensation:
- IX pair: mucosa of the pharynx, tonsils, middle ear, and posterior third of the tongue.
- X pair: dura mater of the posterior cranial fossa, larynx, epiglottis. The vagus nerve also gives off the auricular branch — its only cutaneous branch, which innervates part of the external acoustic meatus and the posterior surface of the auricle.
Taste sensation: The glossopharyngeal nerve collects information from the taste buds of the posterior third of the tongue, and the vagus nerve from the epiglottis.
Parasympathetic (autonomic) system
Autonomic fibers make up a significant part of both nerves and are responsible for the function of glands and smooth muscle.
- Glossopharyngeal nerve: originates from the inferior salivatory nucleus. The fibers run as part of the tympanic nerve, synapse in the otic ganglion, and stimulate the secretion of the parotid salivary gland.
- Vagus nerve: originates from the dorsal nucleus of the vagus nerve (nucleus dorsalis nervi vagi). This is the main parasympathetic nerve of the trunk. It innervates the organs of the neck, thorax (bronchi, heart), and abdominal cavity (stomach, liver, kidneys, intestines down to the left colic flexure).
Its effects include slowing the heart rate, constricting the bronchi, and stimulating peristalsis and gastrointestinal gland secretion.
Clinical manifestations of lesions
Isolated lesions of the IX pair are rare; more often, both nerves are affected together (e.g., in tumors of the posterior cranial fossa, skull base fractures, or aneurysms).
Symptoms of IX nerve lesion:
- Loss of taste (ageusia) on the posterior third of the tongue.
- Decreased pharyngeal and palatal reflexes.
- Moderate dysphagia (swallowing disorder) and dry mouth.
Symptoms of X nerve lesion (unilateral):
- Sagging of the soft palate on the affected side.
- Nasal tone of voice (due to the nasal cavity not being isolated from the oral cavity).
- Deviation of the uvula toward the healthy side when saying "Ah".
- Hoarseness of voice (vocal cord paresis due to recurrent laryngeal nerve dysfunction).
- Autonomic disturbances: tachycardia, arrhythmia.
Briefly: answers to topical questions
What branches does the vagus nerve give off in the cervical region?
On its way to the abdominal cavity, the vagus nerve gives off a number of branches arising at the level of the head and neck.
- Meningeal branch — arises from the superior cervical ganglion to the dura mater.
- Auricular branch — arises from the superior ganglion to the skin of the external acoustic meatus and auricle.
- Pharyngeal branches — form the pharyngeal plexus, innervating the muscles of the pharynx and soft palate.
- Superior laryngeal nerve — arises from the inferior ganglion to the muscles and mucosa of the larynx.
- Recurrent laryngeal nerve — loops around large vessels and returns to the neck to the larynx.
- Superior cervical and thoracic cardiac branches — head toward the cardiac plexus.
What pathway do the parasympathetic fibers of the glossopharyngeal nerve take to the parotid salivary gland?
The parasympathetic fibers to the parotid salivary gland originate in the brainstem and pass through the system of branches of the glossopharyngeal nerve.
- Inferior salivatory nucleus (nucleus salivatorius inferior) — gives rise to preganglionic parasympathetic fibers.
- Tympanic nerve (n. tympanicus) — branches off from the inferior ganglion of the nerve and forms the tympanic plexus.
- Lesser petrosal nerve (n. petrosus minor) — carries fibers from the tympanic plexus.
- Otic ganglion (ganglion oticum) — the site of synapse onto postganglionic fibers that innervate the parotid gland (glandula parotidea).
What branches does the glossopharyngeal nerve give off along its course?
Along its course, the glossopharyngeal nerve gives off a number of branches to innervate structures of the head and neck.
- Tympanic nerve (n. tympanicus) — branches off from the inferior ganglion to the tympanic cavity.
- Sinus branch (branches to the carotid sinus) — innervates the carotid sinus and carotid body.
- Pharyngeal branches — innervate the pharyngeal muscles and mucous membranes.
- Palatine branches — innervate the palatine tonsil (tonsilla palatina).
- Lingual branches — provide taste and general sensation to the posterior third of the tongue.
To remember uvular deviation in X nerve paresis: "The healthy side pulls the blanket over itself." The muscles on the healthy side maintain tone and pull the uvula away from the affected, weak side.
Class and exam questions
Why does the swallowing reflex not disappear in unilateral cerebral cortex lesions?
The motor nucleus ambiguus, which innervates the pharyngeal muscles, receives bilateral cortical innervation. Impulses from the healthy hemisphere fully compensate for the function.
What is the anatomical peculiarity of the recurrent laryngeal nerve?
It has an asymmetrical course. The right nerve loops around the subclavian artery, while the left descends lower into the thoracic cavity and loops around the aortic arch, after which both return upward to the larynx.
Which branch of the vagus nerve is responsible for skin sensation?
Auricular branch. This is the only cutaneous branch of the X pair; it innervates the posterior surface of the auricle and part of the external acoustic meatus.
What else to study on this topic
- Topography of the branches of the vagus nerve in the thoracic and abdominal cavities
- Glossopharyngeal neuralgia: clinical presentation and microvascular decompression
- Involvement of cranial nerves IX and X in blood pressure regulation (carotid sinus and aortic arch)
- Connection of the accessory nerve (CN XI) with the nucleus ambiguus and vagus nerve
- Reflex arcs of coughing, choking, and vomiting
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Other topics in "Chapter 10. Disorders of Swallowing and Phonation. Lesions of the Glossopharyngeal and Vagus Nerves"
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