THE GLOSSOPHARYNGEAL NERVE

It is the 9th Cranial Nerve.

It is a motor and sensory nerve.
Motor fibers supplies Stylopharyngeus
Parasympathetic secretromotor supply to parotid salivary gland.
Sensory fibers including the taste fibers pass to the posterior third of the tongue and the pharynx.

FUNCTIONAL COMPONENTS

Special Visceral Efferent
Fibers arise in nucleus ambiguus and supply Stylopharyngeus. Nucleus ambiguus lies in the medulla.

General Visceral Efferent
Fibers arise in the inferior salivatory nucleus and travel to the Otic ganglion. Postganglionic fibers arising in the ganglion supply the parotid gland.

General Visceral Afferent
Fibers are peripheral processes of cells in the inferior ganglion of the nerve. They carry general sensations (touch, temperature, pain) from the pharynx and the posterior part of the tongue to the ganglion. The central processes convey these sensations to the nucleus of solitary tract.

Special Visceral Afferent
These fibers are also peripheral processes of cells in the inferior ganglion. They carry sensations of taste from the posterior one third of the tongue to the ganglion. The central processes convey these sensations to the nucleus of the solitary tract.

ORIGIN:
It emerges from the anterior surface of upper part of medulla oblongata by three or four rootlets between olive and inferior cerebellar peduncle.
It passes forward and laterally beneath the cerebellum in the posterior cranial fossa and leaves the skull by passing downward through the central part of Jugular foramen.
Superior and inferior sensory ganglia are located on the nerve as it passes through the jugular foramen. It descends in the neck within the carotid sheath. It then winds forward around the stylopharyngeus muscle and passes between superior and middle constrictor muscles.
The lingual branch of nerve enters the submandibular region.

BRANCHES

TYMPANIC BRANCH

It arises from the Glossopharyngeal nerve just below the jugular foramen, passes through the floor of the middle ear and gives off lesser petorsal nerve, lesser petorsal nerve contains secretromotor fibers for parotid gland.
Having entered the skull it leaves through the foramen ovale. The nerve then joins the otic ganglion.

CAROTID BRANCH
It supplies the carotid sinus and carotid body. Carotid body is a chemoreceptor being sensitive to excess carbon dioxide and decreased oxygen.

MUSCULAR BRANCH:
It supplies the stylophyrngeus muscle.

PHARYNGEAL BRANCH:

It unites on the outer surface of middle constrictor muscle with pharyngeal branch of vagus and pharyngeal branch of sympathetic trunk to form the pharyngeal plexus.
By means of these branches the glossophyrngeal nerve gives sensory fibers to the mucous membrane of pharynx, tonsil, and soft palate.

LINGUAL BRANCH

It supplies General sensory and special taste fibers to mucous membrane of posterior third of the tongue and circumvallate papillae region of the anterior of the tongue.
The lingual branch enters the tongue below styloglossus muscle.


EXAMINATION

Most of the functions of the 9th nerve are intermingled with 10th nerve. Taste on the posterior one third of tongue is difficult to test on the bedside.

Sensory Function:

Gag Reflex
Ask the patient to open the mouth and depress the tongue with a spatula. Touch the posterior pharyngeal wall with a stick having cotton wrapped on that end, first on one side of the midline and then the other. There will be contraction and elevation of the pharyngeal wall on that side. The sensory component of this reflex arc is 9th nerve and motor component is 10th nerve.

Palatal Reflex
When soft palate is touched it moves upwards. Each side is tested separately. Pathway is the same as that of gag reflex.

Motor Function:
It cannot be tested independent of 10th nerve.

INTERPRETATION:
Isolated 9th nerve lesion is rare.