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Cranial nerve X is the vagus nerve. The literal translation is “wandering” as it takes a wandering course from the skull to the abdominal cavity. The vagus nerve supplies sensory, special sensory, motor and parasympathetic innervation to structures of the head, neck and thoracoabdominal cavity.
First, we will discuss the embryology of the vagus nerve, followed by the structure, function and clinical relevance of this fascinating nerve.
The vagus nerve then moves inferolaterally with CNs IX and XI to enter the jugular foramen.
Extracranial vagus nerve: head
Upon exiting the jugular foramen, an auricular branch is given off, supplying somatic sensation to the posterior external auditory canal and external ear. This is the only branch of the vagus nerve given to the head.
Extracranial vagus nerve: neck
As the vagus nerve continues to course down the neck, it travels in the carotid sheath, posterior to the common carotid artery and internal jugular vein.
The following branches leave the vagus nerve as it descends the neck (superior to inferior).
Supplies motor innervation to most of the soft palate and pharynx.
Superior laryngeal nerve
Internal branch: sensory innervation to thelaryngopharynx and superior larynx (including taste to the epiglottis)
External branch: motor innervation to the cricothyroideus muscle
Right recurrent laryngeal nerve (branches from the vagus in the neck)
Loops under the right subclavian artery and ascends to the larynx. Provides motor innervation to most laryngeal muscles.
Clinical relevance: vagus nerve examination
The vagus nerve has many functions, but we really only test one of these: the efferent (motor) limb of the cough or gag reflexes.
By stimulating the oropharynx with a long cotton tip, the efferent limb of the gag reflex causes the muscles of the pharynx to gag in an attempt to rid this region of the foreign object. During coughing, the vagus nerve provides motor input to roughly the same muscles to constrict the pharynx and allow high velocity, forceful coughing.
Extracranial vagus nerve: thorax
Towards the base of the neck, both the left and right vagus nerves take different paths.
Left vagus nerve
The left vagus nerve passes between the left common carotid artery and the left subclavian artery. It then enters the thorax posterior to the sternoclavicular joint and forms the anterior vagal trunk.
Right vagus nerve
The right vagus nerve passes anterior to the right subclavian artery. It enters the thorax posterior to the sternoclavicular joint and forms the posterior vagal trunk.
Anterior and posterior vagal trunks
Branches from the vagal trunk contribute to the oesophageal plexus, supplying motor innervation to this muscular structure.
In the thorax, two branches arise from the anterior and posterior vagal trunks.
Left recurrent laryngeal nerve (branches from the anterior vagal trunk in the thorax)
The left recurrent laryngeal nerve loops under the arch of the aorta and ascends into the larynx. It provides motor innervation to intrinsic laryngeal muscles.
The cardiac branches provide parasympathetic and visceral innervation to the heart.
Clinical relevance: refractory tachycardia
We also know that the vagus nerve supplies the sinoatrial and atrioventricular nodes of the heart with parasympathetic innervation. Patients who lose vagal tone may lose the parasympathetic tone in these regions, allowing uncontrolled sympathetic activity presenting as a refractory tachycardia. While quite rare, keep this in the back of your mind!
Extracranial vagus nerve: abdomen
Both the left and right vagal trunk enter the abdomen through the oesophageal hiatus at the vertebral level of T10.
In the abdomen, the vagus nerve terminates as many parasympathetic and sensory branches supplying the oesophagus, stomach, small intestine, and the distal 2/3 of the colon.
CN X is the vagus nerve
It originates in the medulla oblongata
Its major role is parasympathetic innervation of the viscera
The recurrent laryngeal nerve loops under the right subclavian artery and (left) aortic arch
It passes through the jugular foramen with CN IX and XI
It provides many fibre types, each of which are shown in the table below
General somatic afferent
Special visceral afferent
General visceral afferent
General visceral efferent
Special visceral efferent
Skin around ear
Taste and sensation to the epiglottis
Sensory information to body viscera
Parasympathetic to glands of GI tract
Motor innervation to soft palate, pharynx and larynx
Sinnatamby, C. S. (2011). Last’s Anatomy, International Edition: Regional and Applied. Elsevier Health Sciences.
Moore, K. L., Dalley, A. F., & Agur, A. M. (2013). Clinically oriented anatomy. Lippincott Williams & Wilkins.
Nolte, J. (2002). The human brain: an introduction to its functional anatomy.
Snell, R. S. (2010). Clinical neuroanatomy. Lippincott Williams & Wilkins.
Patrick J. Lynch. License: [CC BY]. Modified by Dr Lewis Potter.