Glossopharyngeal nerve

Number: IX

Name: Glossopharyngeal

Sensory, motor, or both: Both sensory and motor

Origin/Target: Medulla

Nuclei: Nucleus ambiguus, Inferior salivary nucleus, Solitary nucleus

Function: Receives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus. Some sensation is also relayed to the brain from the palatine tonsils. Located in the jugular foramen.

Description:

The glossopharyngeal nerve contains both motor and sensory fibers, and is distributed, as its name implies, to the tongue and pharynx. It is the nerve of ordinary sensation to the mucous membrane of the pharynx, fauces, and palatine tonsil, and the nerve of taste to the posterior part of the tongue. It is attached by three or four filaments to the upper part of the medulla oblongata, in the groove between the olive and the inferior peduncle.

The sensory fibers arise from the cells of the superior and petrous ganglia, which are situated on the trunk of the nerve, and will be presently described. When traced into the medulla, some of the sensory fibers, probably sympathetic afferent, end by arborizing around the cells of the upper part of a nucleus which lies beneath the ala cinerea in the lower part of the rhomboid fossa. Many of the fibers, probably the taste fibers, contribute to form a strand, named the fasciculus solitarius, which descends in the medulla oblongata. Associated with this strand are numerous nerve cells, and around these the fibers of the fasciculus end. The somatic sensory fibers, few in number, are said to join the spinal tract of the trigeminal nerve.

The somatic motor fibers spring from the cells of the nucleus ambiguus, which lies some distance from the surface of the rhomboid fossa in the lateral part of the medulla and is continuous below with the anterior gray column of the medulla spinalis. From this nucleus the fibers are first directed backward, and then they bend forward and lateralward to join the fibers of the sensory root. The nucleus ambiguus gives origin to the motor branches of the glossopharyngeal and vagus nerves, and to the cranial part of the accessory nerve.

The sympathetic efferent fibers from the nucleus beneath the ala cinerea, the dorsal nucleus, are probably both preganglionic motor fibers and preganglionic secretory fibers of the sympathetic system. The secretory fibers pass to the otic ganglion and from it secondary neurons are distributed to the parotid gland. Some authors describe these fibers as arising from a distinct nucleus the inferior salivatory nucleus, which lies near the dorsal nucleus.

From the medulla oblongata, the glossopharyngeal nerve passes lateralward across the flocculus, and leaves the skull through the central part of the jugular foramen, in a separate sheath of the dura mater, lateral to and in front of the vagus and accessory nerves. In its passage through the jugular foramen, it grooves the lower border of the petrous part of the temporal bone; and, at its exit from the skull, passes forward 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 and Constrictor pharyngis medius. Thence it passes under cover of the Hyoglossus, 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.

In passing through the jugular foramen, the nerve presents two ganglia, the superior and the petrous:

• The Superior Ganglion (ganglion superius; jugular ganglion) is situated in the upper part of the groove in which the nerve is lodged during its passage through the jugular foramen. It is very small, and is usually regarded as a detached portion of the petrous ganglion.
• The Petrous Ganglion (ganglion petrosum; inferior ganglion) is larger than the superior and is situated in a depression in the lower border of the petrous portion of the temporal bone.

Branches of Communication.—The glossopharyngeal nerve communicates with the vagus, sympathetic, and facial.