Equal, symmetrical and belonging to the category of mixed nerves, the glossopharyngeal nerve arises at the level of the brainstem; from here, after a slight lateral deviation, it wedges into the jugular foramen of the temporal bone, emerges from the skull and descends along the neck to reach the pharynx.
During this journey, the glossopharyngeal nerve gives rise to different branches, which allow it to connect to other peers of the body, in addition to the aforementioned pharynx.
The glossopharyngeal nerve innervates the middle ear, the inner surface of the eardrum and the Eustachian tube; innervates the posterior portion of the tongue and controls gustatory sensitivity; innervates the carotid sinus and the carotid body; innervates the palatine tonsils and mucous membrane of the " oropharynx; finally, it innervates the stylopharyngeal muscle and the parotid gland.
- Motor (or efferent) nerves. The nerves intended to control muscles and glands are motor;
- Sensory (or afferent) nerves. The nerves responsible for controlling the sensitivity of the organs of the body, in particular the skin, sense organs and mucous areas, are sensitive;
- Mixed nerves, i.e. they play the role of both motor and sensory nerves.
Remember that the word "nerve" identifies a grouping of several axons; also known as neuritis or nerve fiber, the axon is the characteristic extension of the nerve cell (or neuron), which allows the latter to communicate with other nerve cells or organs located even at long distances.
temporal and escape from the skull.
Once out of the skull, the glossopharyngeal nerve descends along the neck to reach the pharyngeal districts.
Along its path, the glossopharyngeal nerve gives rise to numerous branches (or ramifications), some motor and others sensitive.
Origin of the Glossopharyngeal Nerve
Going into the details of its origin, the glossopharyngeal nerve arises at the level of the anterior portion of the medulla oblongata; preceded in the order by the bridge of Varolius and the midbrain, the medulla oblongata represents the inferior (or distal) section of the brainstem.
Course of the Glossopharyngeal Nerve
Once emerged from the medulla oblongata, the glossopharyngeal nerve lies within the confines of the posterior cranial fossa; here, after having made a slight lateral movement, it passes in the vicinity of the cerebellar floccule - a small lobe of the cerebellum - and starts to pass through the jugular foramen.
The jugular foramen is an "opening in the temporal bone."
In "crossing the jugular foramen, the glossopharyngeal nerve is not alone: accompanying it are the vagus nerve (X cranial nerve) and the accessory nerve (XI cranial nerve), which will clearly follow different paths.
Immediately after the jugular foramen, the glossopharyngeal nerve widens in two points located a short distance from each other; these two enlargements of the nerve are the so-called superior ganglion and inferior ganglion, and they enclose the neurons connected to the axons with sensory function.
After the two ganglia, the glossopharyngeal nerve descends along the neck, in an anterolateral position with respect to the internal carotid artery and passing near the styloid process of the temporal bone; when it reaches the level of the pharynx, approximately where the stylopharyngeal muscle resides, it forms a slight curve, transits inferiorly to the ioglossus muscle (extrinsic muscle of the tongue) and concludes its course by dividing itself between the palatine tonsils, the mucosa of the oropharynx and the posterior portion of the language.
Branches of the Glossopharyngeal Nerve
The branches of the glossopharyngeal nerve expand the number of areas reached by the latter.
The branches of the glossopharyngeal nerve include:
- The tympanic nerve. It emerges shortly after the glossopharyngeal nerve has passed through the jugular foramen; this branch goes up to the ear, where, after having formed the so-called tympanic nerve plexus (or tympanic plexus), it innervates the middle ear, the inner surface of the eardrum and the Eustachian tube.
The tympanic nerve is a sensory branch (of the glossopharyngeal nerve). - The small petrosal nerve. For a while, this branch is in common with the tympanic nerve and with the tympanic nerve plexus; after that, it becomes independent, passes through the so-called optic ganglion and reaches the parotid gland, obviously in order to control its functioning.
The small petrosal nerve is a motor branch (of the glossopharyngeal nerve) having parasympathetic activity. - The carotid sinus nerve. It arises when the glossopharyngeal nerve is located in the vicinity of the stylopharyngeal muscle; this branch descends along the neck, until it reaches, for innervation, the carotid sinus (vascular structure involved in the regulation of blood pressure) and the carotid body (chemoceptor organ sensitive to the concentration of oxygen in the blood).
The carotid sinus nerve is a sensory branch (of the glossopharyngeal nerve). - The pharyngeal branch of the glossopharynx. Terminal branch of the glossopharyngeal nerve, connects to some branches of the vagus nerve (X cranial nerve), to form the so-called pharyngeal nerve plexus (or pharyngeal plexus) and innervate the mucosa of the oropharynx.
The pharyngeal nerve is a sensitive branch (of the glossopharyngeal nerve). - The lingual branch of the glossopharyngeal. Another terminal branch of the glossopharyngeal nerve, innervates the posterior 1/3 of the tongue, guaranteeing the gustatory sensitivity of this area.
The lingual nerve is a sensory branch (of the glossopharyngeal nerve). - The tonsillar branch of the glossopharyngeal. Another terminal branch of the glossopharyngeal nerve is destined to reach and innervate the palatine tonsils.
The tonsillar nerve is a sensory branch (of the glossopharyngeal nerve). - The stylopharyngeal nerve (or stylopharyngeal branch). This branch of the glossopharyngeal nerve is intended to reach and innervate the stylopharyngeal muscle, a key muscle for swallowing.
The glossopharyngeal nerve is a motor branch (of the glossopharyngeal nerve).
Glossopharyngeal Nerve and Nervous Plexus
To understand…
A nerve plexus is a collection of nerve fibers belonging to different nerves; the same plexus can comprise nerve fibers of motor nerves and nerve fibers of sensory nerves.
As anticipated in the description of the branches, the glossopharyngeal contributes to the formation of two nerve plexuses: the tympanic plexus and the pharyngeal plexus.
In addition to the branches of the glossopharyngeal nerve known as the tympanic nerve and the lesser petrosal nerve, the tympanic plexus includes the greater petrosal nerve, a branch of the facial nerve (or 7th cranial nerve).
In addition to the pharyngeal branch of the glossopharyngeal nerve, the pharyngeal plexus comprises the pharyngeal branch of the vagus nerve (or X cranial nerve).
and pharynx.The parotid gland, on the other hand, is under the control of the lesser petrosal nerve; this gland is the most voluminous of the salivary glands, ie the glands responsible for the production of saliva.
Sensitive Functions of the Glossopharyngeal Nerve
The sensory functions of the glossopharyngeal nerve include:
- Sensitivity control at the level of the palatine tonsils. This function is presided over by the tonsillar branch of the glossopharyngeal;
- The control of sensitivity in the oropharyngeal mucosa. Fundamental for this function is the pharyngeal branch of the glossopharyngeal;
- The control of the sensitivity and gustatory capacity of the posterior 1/3 of the tongue. This function is provided by the lingual branch of the glossopharyngeal;
- The control of sensitivity at the level of the middle ear, the inner surface of the eardrum and the Eustachian tube. The branch known as the tympanic nerve is responsible for this function;
- The control of sensitivity at the level of the carotid sinus and the carotid body. This function is provided by the branch known as the carotid sinus nerve.
It should be noted that the sensitivity control at the level of the oropharyngeal mucosa is connected to the vomiting reflex: the contact of this area by a foreign object (eg: a finger), in fact, triggers the so-called retching.
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