Course
- The vagus nerve emerges from the medulla to exit the skull through the jugular foramen, accompanied by the CN9 and CN11.
- The cell bodies of its sensory fibers are located in the superior and inferior ganglia, which lie within the jugular fossa of the petrous (temporal) bone.
- As it descends into the neck, the vagus passes through the carotid sheath (dorsal), alongside the internal jugular vein (ventrolateral) and the internal carotid artery (ventromedial).
Arnold’s Nerve
- Source: ACNR
- Aka:
- Auricular branch of the vagus
- Alderman’s nerve
- Is the remnant of the embryonic nerve that supplies the first branchial arch, which includes the external acoustic meatus, middle ear and auditory tube.
- Conveys sensation from the tragus and external acoustic meatus
- Course
- Arises from the superior jugular ganglion of the CN10
- Joined by a filament from the inferior (petrous) ganglion of the CN9
- A mixed general somatic afferent nerve composed of vagal, glossopharyngeal, and facial nerve fibres
- Arnold’s canal— the passage in the petrous temporal bone for Arnold’s nerve
Function
- Five functional components make up the vagus nerve (X):
Components | Ganglia | Nuclei | Exit through Skull | Target Organ | Function |
Somatic motor | ㅤ | Nucleus ambiguus | Jugular foramen | Muscles of the larynx and pharynx | Speech and swallowing |
Visceral motor | Various | Dorsal motor nucleus of the vagus | ㅤ | Thoracic and abdominal viscera | Various autonomic (parasympathetic) effects on visceral organs |
Somatic sensory | Superior | Spinal trigeminal tract | ㅤ | External ear | Somatic sensation |
Visceral sensory | Inferior | Solitary tract | ㅤ | Pharynx, larynx, aortic arch and body, thoracic and abdominal viscera | Visceral sensation |
Special sense | ㅤ | ㅤ | ㅤ | Pharynx | Taste |
- Somatic motor fibers
- have their cell bodies in the nucleus ambiguus.
- They supply the majority of the muscles of the pharynx and larynx, which are responsible for swallowing and the production of speech
- Exceptions:
- Glossopharyngeal nerve supplies the stylopharyngeus muscle, which elevates the pharynx but does not participate in swallowing;
- Trigeminal nerve supplies the tensor veli palatini, which tenses the soft palate, thus opening the auditory tube, as occurs in the act of yawning.
- Special sensory fibers
- Have their cell bodies in the inferior ganglion.
- Carry taste-related impulses from the posterior pharynx that terminate in the nucleus of the solitary tract.
Clinical
- Unilateral lesions of the nucleus ambiguus cause
- Hoarseness
- Dysphagia
- Tachycardia
- Deviation of the uvula to the side opposite the lesion.
- Unilateral lesions of the dorsal motor nucleus
- Are not manifest clinically
- But bilateral lesions are life threatening.
- The recurrent laryngeal nerve
- Supplies all the intrinsic muscles of the larynx except the cricothyroid muscle.
- Cricothyroid muscle supplied by superior laryngeal nerve
- Para-tracheal lymphadenopathy or an aortic aneurysm may compress the recurrent laryngeal nerve, causing hoarseness secondary to paralysis of the vocal cords.
- Hering-Breuer inflation reflex
- A reflex that is stimulated by stretch receptors in the bronchi and bronchioles.
- The afferent arm of the reflex is via the vagus nerve and inhibits the dorsal respiratory nucleus in the dorsal medulla to stop inspiration if the lungs are overly distended.
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