LYKA BERNAL AND NAND PRAKASH

Cranial Nerves

Cranial IX : Glossopharyngeal Nerve Embryologically, the glossopharyngeal

nerve is associated with the derivatives of the third pharyngeal arch.

Both Sensory and Motor Nerve Have 3 nuclei:

1. Main motor nucleus2. Parasympathetic Nucleus3. Sensory Nucleus

MAIN MOTOR NUCLEUS The motor fibers' origin is the medulla oblongata The motor division sends information to the: The parotid gland The muscles in the throat The nerve bundles (plexus) in the throat The stylopharyngeus muscle of the pharynx is

innervated by the glossopharyngeal nerve. This muscle acts to shorten and widen the pharynx, and elevate the larynx during swallowing.

PARASYMPATHETIC NUCLEUS also called Inferior Salivatory NucleusAFFERENT PARASYMPATHETIC

FIBERS EFFERENT PREGANLIONIC PARASYMPATHETIC FIBER

Receives from hypothalamus through descending autonomic pathway

RECEIVES INFORMATION FROM:Olfactory system through Reticular FormationConcerning taste received from Nucleus of Solitary tract from mouth cavity

Visceral sensory (general visceral afferent) carries visceral sensory information from the carotid sinus and body

Reach Otic Ganglion through tympanic branch of the Glossopharyngeal nerve, the tympanic plexus, and the lesser petrosal nerve.

Visceral motor (general visceral efferent) provides parasympathetic innervation of the parotid gland

SENSORY NUCLEUS Part of nucleus of the tractus solitarus

The sensory division of the glossopharyngeal nerve receives information from:

The pharynx (part of the throat) The posterior third of the tongue The parotid salivary gland The middle ear

The glossopharyngeal nerve provides sensory innervation a variety of structures in the head and neck.

Overview of the branches of the glossopharyngeal nerve. The tympanic nerve arises as the nerve traverses the

jugular foramen. It penetrates the temporal bone and enters the cavity of the middle ear. Here, it forms the tympanic plexus – a network of nerves that provide sensory innervation to themiddle ear, internal surface of the tympanic membrane and Eustachian tube.

At the level of the stylopharyngeus, thecarotid sinus nerve arises. It descends down the neck to innervates both the carotid sinus and carotid body, providing information regarding blood pressure and oxygenation respectively.

The glossopharyngeal nerve terminates by splitting into several sensory branches:

Pharyngeal branch – combines with fibres of the vagus nerve to form the pharyngeal plexus. It innervates the mucosa of the oropharynx.

Lingual branch – provides the posterior 1/3 of the tongue with general and taste sensation

Tonsillar branch – forms a network of nerves, known as the tonsillar plexus, which innervates the palatine tonsils.

. It also projects into many different structures in the brainstem:

Solitary nucleus: Taste from the posterior one-third of the tongue and information from carotid baroreceptors and carotid body chemoreceptors

Spinal nucleus of the trigeminal nerve: Somatic sensory fibers from the middle ear

Lateral Nucleus of Ala Cinerea: Visceral pain Nucleus ambiguus: The lower motor neurons for the 

stylopharyngeus muscle Inferior salivatory nucleus: Parasympathetic input to the 

parotid and mucous glands.

ual, tonsil and pharyngeal.

PATHWAY From the anterior portion of the medulla oblongata, the glossopharyngeal

nerve passes laterally across or below the flocculus, and leaves the skull through the central part of the jugular foramen. From the superior and inferior ganglia in jugular foramen it has its own sheath of dura mater. The inferior ganglion on the inferior surface of petrous part of temporal is related with a triangular depression into which the aqueduct of cochlea opens. On the inferior side, the glossopharyngeal nerve is lateral and anterior to the vagus nerve and accessory nerve.

In its passage through the jugular foramen (with X and XI), it passes between the internal jugular vein and internal carotid artery. It descends in front of the latter vessel, and beneath the styloid process and the muscles connected with it, to the lower border of the stylopharyngeus. It then curves forward, forming an arch on the side of the neck and lying upon the stylopharyngeus andmiddle pharyngeal constrictor muscle. From there, it passes under cover of the hyoglossus muscle, and is finally distributed to the palatine tonsil, the mucous membrane of the fauces and base of the tongue, and the mucous glands of the mouth

CLINICAL RELEVANCE – GAG REFLEX The glossopharyngeal nerve supplies

sensory innervation to the oropharynx, and thus carries the afferent information for the gag reflex. When a foreign object touches the back of the mouth, this stimulates CNIX, beginning the reflex. The efferent nerve in this process is the vagus nerve, CNX.

An absent gag reflex signifies damage to the glossopharyngeal nerve.

EFFECTS OF DAMAGE AND CLINICAL TEST

The Glossopharyngeal nerve if damaged can have several effects on the human body. These effects include loss of bitter and sour taste, and impaired swallowing. The clinical tests to see if the Glossopharyngeal nerve has been damaged includes testing the gag reflex of the mouth. Ask the patient to swallow or cough, and Other signs include speech impediments. Finally, test the posterior one-third of the tongue with bitter and sour substances.