Vagal System

2. • The glossopharyngeal nerve, the vagus nerve, and the
cranial portion of the accessory nerve that these
nerves are together known as a single “vagal system”
• They all are mixed nerves, and some of their
components arise from common brainstem nuclei
(the nucleus ambiguus and nucleus solitarius)
• The glossopharyngeal, vagal, and accessory nerves
exit the skull together through the jugular foramen

3. GLOSSOPHARYNGEAL NERVE
• The glossopharyngeal nerve is the 9th paired mixed cranial nerve.
• ORIGIN- in the medulla oblongata of the brain. It emerges from the
anterior aspect of the medulla, moving laterally in the posterior cranial
fossa.
• EXIT -The nerve leaves the cranium via the jugular foramen
• GANGLIA- Immediately outside the jugular foramen lie two ganglia
(collections of nerve cell bodies).They are known as
the superior and inferior (or petrous) ganglia – they contain the cell
bodies of the sensory fibres in the glossopharyngeal nerve.
• The nerve enters the pharynx by passing between the superior and middle
pharyngeal constrictors. Within the pharynx, it terminates by dividing
into several branches
1. Pharyngeal branch – combines with fibres of the vagus nerve to form the
pharyngeal plexus. It innervates the mucosa of the oropharynx
2. Lingual branch – provides the posterior 1/3 of the tongue with general
and taste sensation
3. Tonsillar branch – forms a network of nerves, known as the tonsillar
plexus, which innervates the palatine tonsils.

4. Function
• It is a mixed nerve:
1. Sensory: Innervates the oropharynx, carotid body and sinus, posterior 1/3 of the
tongue, middle ear cavity and Eustachian tube.
2. Special sensory: Provides taste sensation to the posterior 1/3 of the tongue.
3. Parasympathetic: Provides parasympathetic innervation to the parotid gland.
4. Motor: Innervates the stylopharyngeus muscle that acts to shorten and widen
the pharynx and elevate the larynx during swallowing.

5. Glossopharyngeal nerve lesions
Glossopharyngeal nerve lesions produce:
 difficulty swallowing
 impairment of taste over the posterior one-third of the tongue and palate;
 impaired sensation over the posterior one-third of the tongue, palate, and
pharynx
 an absent gag reflex
 dysfunction of the parotid gland.

6. Glossopharyngeal Neuralgia
• Characterized by a sharp, jabbing pain deep in the throat, or in the tongue, ear,
and tonsils, lasting a few seconds to a few minutes.
• CAUSE- small blood vessel that presses on the nerves as they exit the brainstem.
This condition is caused by irritation of the ninth cranial nerve by a blood vessel,
and is most commonly seen in people over age 40
• Attacks may be triggered by a particular action, such as chewing, swallowing,
talking, yawning, coughing, or sneezing.
• DIAGNOSIS-
1. For the test, a doctor touches the back of the throat with a cotton-tipped
applicator. If pain results, the doctor applies a local anesthetic to the back of the
throat. If the anesthetic eliminates the pain, glossopharyngeal neuralgia is likely.
2. Magnetic resonance imaging (MRI) is done to check for tumors.
• TREATMENT - anticonvulsant medications, such as carbamazepine, gabapentin
etc.

7. VAGUS NERVE
• The vagus is the 10th cranial nerve and the longest nerve of the
autonomic nervous system in the human body and comprises
sensory and motor fibers.
• ORIGIN- from neurons of the nodose ganglion, whereas the motor
fibers come from neurons of the dorsal motor nucleus of theVagus
and the nucleus ambiguus.
• It is also known asWandering nerve
NUCLEI
• The dorsal nucleus of vagus nerve – which sends parasympathetic
output to the viscera, especially the intestines
• The nucleus ambiguus – which gives rise to the branchial efferent
motor fibers of the vagus nerve and preganglionic parasympathetic
neurons that innervate the heart
• The solitary nucleus – which receives afferent taste information
and primary afferents from visceral organs
• The spinal trigeminal nucleus – which receives information about
deep/crude touch, pain, and temperature of the outer ear, the dura
of the posterior cranial fossa and the mucosa of the larynx

8. Function
• Sensory: Innervates the skin of the external acoustic meatus and the internal
surfaces of the laryngopharynx and larynx. Provides visceral sensation to the heart
and abdominal viscera.
• Special Sensory: Provides taste sensation to the epiglottis and root of the tongue.
• Motor: Provides motor innervation to the majority of the muscles of the pharynx,
soft palate and larynx.
• Parasympathetic: Innervates the smooth muscle of the trachea, bronchi and
gastro-intestinal tract and regulates heart rhythm.

9. Vagus Nerve Lesion
• The soft palate is left hanging down on the side of the lesion
• The gag reflex is diminished, and the patient’s speech is nasal because the nasal
cavity can no longer be closed off from the oral cavity.
• Paresis of the pharyngeal constrictor muscle causes the palatal veil to be pulled
over to the normal side when the patient speakes
• Hoarseness of the voice due to paresis of the vocal folds (lesion of the recurrent
laryngeal nerve with paresis of the internal muscles of the larynx, with the
exception of the cricothyroid muscle).
• Dysphagia and occasionally tachycardia, and cardiac arrhythmia

10. ACCESSORY NERVE
• The accessory nerve is the 11th paired cranial nerve. It has a
purely somatic motor function, innervating the
sternocleidomastoid and trapezius muscles.
• The accessory nerve is divided into spinal and cranial parts
Cranial Component
• The cranial portion arises from the lateral aspect of
the medulla oblongata.
• It leaves the cranium via the jugular foramen, where it briefly
contacts the spinal part of the accessory nerve.
• Immediately after leaving the skull, cranial part combines
with the vagus nerve (CN X) at the inferior ganglion of vagus
nerve (a ganglion is a collection of nerve cell bodies).
• The fibres from the cranial part are then distributed through
the vagus nerve. For this reason, the cranial part of the
accessory nerve is considered as part of the vagus nerve.

11. Function
The spinal accessory nerve innervates two muscles – the sternocleidomastoid and trapezius.
Sternocleidomastoid
• Attachments – Runs from the mastoid process of the temporal bone to the manubrium
(sternal head) and the medial third of the clavicle (clavicular head).
• Actions – Lateral flexion and rotation of the neck when acting unilaterally, and extension
of the neck at the atlanto-occipital joints when acting bilaterally.
Trapezius
• Attachments – Runs from the base of the skull and the spinous processes of the C7-T12
vertebrae to lateral third of the clavicle and the acromion of the scapula.
• Actions – It is made up of upper, middle, and lower fibres.The upper fibres of the trapezius
elevate the scapula and rotate it during abduction of the arm.The middle fibres retract the
scapula and the lower fibres pull the scapula inferiorly.

12. Accessory Nerve Lesion
• Sternocleidomastoid muscle is paralyzed whileTrapezius
muscle is affected only in its upper half, because it also
receives innervation from the spinal nerves of segments C2
through C4.
• Injury to the accessory nerve distal to the
sternocleidomastoid muscle causes weakness of the
trapezius muscle exclusively.
• Patient has difficulty turning the head to the opposite
side.Weakness of the trapezius muscle causes a shoulder
drop.
• Scapula is displaced downward and outward to the side of
lesion.Lateral raising of the arm beyond 90° is impaired.
• Simple visual inspection of a patient with an accessory
nerve palsy reveals atrophy of the sternocleidomastoid
muscle as well as a drooping shoulder.
• Bilateral weakness makes it difficult to hold the head
erect or to raise the head when lying supine.