The sensation to our pharynx is important for our gag reflex. The glossopharyngeal nerve is the 9^th cranial nerve, and leaves the cranial cavity through the jugular foramen, along with cranial nerves 10 and 11. It has a number of crucial roles, including supplying supplies taste and sensation to the posterior one third of the tongue, and sensation to the pharynx. It also innervates the baroreceptors in the carotid sinus, which is important for blood pressure regulation.

The glossopharyngeal nerve is also known as cranial nerve 9. It arises from the brainstem, the medulla to be precise. It emerges lateral to the olive (an ovaloid structure responsible for pathways of motor learning and hearing). The nerve leaves the skull through the jugular foramen, along with cranial nerves 10 and 11. It passes between the internal jugular vein and the internal carotid artery. It will pass inferiorly, anterior to the internal carotid artery. The branchial motor component of the nerve curves anteriorly and lies upon the stylopharyngeus muscle (which it innervates) that elevates the pharynx during swallowing and speech. It also innervates the middle pharyngeal constrictor.

 

The general sensory component of the nerve arises from the pharyngeal branches of the nerve, which ascends through the jugular foramen, enters the medulla, and synapses in the anterolateral thalamus, then to the posterior limb of the internal capsule, and then to the primary somatosensory cortex (postcentral gyrus). It provides sensation to the posterior one third of the tongue (including circumvallate papillae), inner surface of the tympanic membrane, pharynx, as well as taste to the posterior one third of the tongue. The special sensory component of the nerve (taste), follows the same course into the skull, but synapses in the tractus solitarius and the gustatory component of the nucleus solitarius. Next the fibers connect with the ventral posteromedial nuclei of the thalamus, and then to the inferior third of the primary somatosensory cortex (taste/gustatory cortex).

 

The visceral component of the nerve enters the petrous portion of the temporal bone and runs upwards to reach the tympanic cavity. It forms a plexus in the tympanic cavity, which gives rise to the lesser petrosal nerve. This nerve will re-enter the middle cranial fossa and will pass through the temporal bone to emerge into the middle cranial fossa lateral to the greater petrosal nerve. The nerve will the leave the skull via the foramen ovale along with the mandibular division of the trigeminal nerve. The lesser petrosal nerve provides parasympathetic innervation to the parotid gland via the otic ganglion (which is attached to the mandibular division just as it leaves the foramen ovale), which releases saliva into the oral cavity via its duct that opens in the cheek opposite the second upper molar.

 

The visceral sensory component collects information from carotid sinus and body. The information ascends via the sinus nerve, and joins the glossopharyngeal nerve to run up into the skull via the jugular foramen. Once the nerve enters the skull it enters the lateral medulla, and descends in the tractus solitarius and synapses in the nucleus solitarius. Here the fibers connect to the hypothalamus and reticular formation to modulate cardiovascular and respiratory parameters, blood pressure and serum oxygen and carbon dioxide concentrations.

Developmental precursor for motor division- Basal plate of the medulla oblongata (Myelencephalon- secondary brain vesicle).

Developmental precursor for sensory division- Cranial neural crest

Muscles- Stylopharyngeus

Sensation- Posterior one third of the tongue, Pharynx. Special sense (taste) posterior third of the tongue.

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The glossopharyngeal nerve is the 9^th cranial nerve, and leaves the cranial cavity through the jugular foramen. The nerve supplies taste and sensation to the posterior one third of the tongue, and sensation to the pharynx.

1.     Frank H.Netter MD: Atlas of Human Anatomy, 5^th Edition, Elsevier Saunders, Chapter 1 Head and Neck

 

2.     Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12^th Edition, Churchill Livingstone Elsevier

 

3.     Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2^nd Edition, Churchill Livingstone Elsevier

 

4.     Elliiot L.Manchell: Gray's Clinical Neuroanatomy: The Anatomic Basis for Clinical Neuroscience

 

5.     The Definitive Neurological Surgery Board Review

By Shawn P. Moore, 2005

 

6.     Human Neuroanatomy

By James R. Augustine, 2008