The Mandibular - Vc or VIII by Prof. Dr. Imran Qureshi The is the third and largest division of the . It is a mixed nerve. Its sensory root emerges from the posterior region of the semilunar ganglion and is joined by the motor root of the trigeminal nerve. These two nerve bundles leave the through the and unite immediately to form the trunk of the mixed mandibular nerve that passes into the . Here, it runs anterior to the middle meningeal and is sandwiched between the superior head of the lateral pterygoid and tensor veli palatini muscles. After a short course during which a meningeal branch to the dura mater, and the nerve to part of the (and the tensor tympani and tensor veli palatini muscles) are given off, the mandibular trunk divides into a smaller anterior and a larger posterior division. The anterior division receives most of the fibres from the motor root and distributes them to the other i.e. the lateral pterygoid, medial pterygoid, temporalis and masseter muscles. The nerve to masseter and two deep temporal (anterior and posterior) pass laterally above the medial pterygoid. The nerve to the masseter continues outward through the , while the turn upward deep to temporalis for its supply. The sensory fibres that it receives are distributed as the . The

1 | P a g e buccal nerve passes between the medial and lateral pterygoids and passes downward and forward to emerge from under cover of the masseter with the . it continues forward to supply the skin in the region of the angle of the month and to a corresponding area of the lining the . The posterior division is mostly sensory and gives origin to the inferior alveolar, lingual and auriculotemporal nerves. It receives only a few motor fibres that are distributed, by the mylohyoid branch of the inferior to the mylohyoid and the anterior belly of digastric muscles. : This nerve arises from the posterior trunk of the mandibular nerve either by two roots, which surround the or as a single nerve, which later on splits to surround the artery. It is directed posteriorly, deep to the running on the medial aspect of the of the . From here it passes upwards and outwards, between the and the cartilage of the external auditory meatus, and in the substance of the . It finally emerges from the gland and ascends over the with the superficial temporal artery to terminate by supplying the skin of the temporal region and the lateral part of the

In its course the auriculotemporal nerve gives cutaneous branches to the external auditory meatus, the anterior part of the tympanic membrane, the tragus of the pinna and a variable, but usually small area of the anterior and upper part of the pinna itself. It joins the superficial temporal vessels and travels with them across the root of the zygomatic arch into the superficial fascia of the scalp. It also supplies twigs to the temporomandibular joint, and carries secretomotor fibres from the to the parotid gland. The detail of these fibers is as under:

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Immediately below foramen ovale, deep to VIII, is a tiny clump of parasympathetic ganglion cells called the “Otic ganglion”.

The Otic ganglion receives its preganglionic input from a branch of the glossopharyngeal nerve. A small twig connects the Otic ganglion to the auriculotemporal branch of VIII. This twig carries the postganglionic axons into the auriculotemporal nerve, which then carries them behind the neck of the mandible into proximity with the parotid gland.

Here the postganglionic parasympathetic axons leave to innervate the parotid gland.

The two largest branches of the mandibular nerve (Inferior Alveolar and Lingual. They continue the downward course of their parent nerve and, thus, are carried deep to the lateral pterygoid muscle.

THE : This is the largest branch of the mandibular nerve. From its origin it passes downwards and follows an almost vertical course behind the , on the outer surface of the medial pterygoid muscle and deep to the lateral pterygoid muscle, and then between the mandibular ramus and the Sphenomandibular ligament to enter the mandibular canal.

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The inferior alveolar nerve passes forwards in the mandibular canal, in company with the , and distributes branches to the lower molar and premolar teeth and the adjacent parts of the gingiva. At the level of mental foramen, it divides into an incisive branch, which continues forwards in the mandible to supply the canine and incisor teeth, and the larger mental branch, which passes out of the bony canal by the mental foramen and is distributed to the skin and subcutaneous tissues of the region and the lower . Just before entering the , the Inferior Alveolar nerve gives off a slender twig from its posterior surface, the Nerve to the Mylohyoid. The nerve to mylohyoid pierces the Sphenomandibular ligament and then turns forward in the space between the medial pterygoid muscle and the mandibular ramus. At the anterior border of medial pterygoid, the Nerve to the Mylohyoid encounters the back edge of the , and then passes onto its superficial surface. Besides supplying the mylohyoid, the nerve also innervates the anterior belly of digastric. THE LINGUAL NERVE: This nerve passes downwards and forwards anterior to the inferior alveolar nerve and between the lateral and medial pterygoid muscles. Near its origin, the nerve, which is a branch of the , joins it from behind. The lingual nerve inclines obliquely to the side of the , passing over the mandibular attachment of the superior constrictor muscle of the . Here the nerve lies against the deep surface of the mandible on the medial side of the roots of the third lower molar tooth and above the deep part of the submandibular gland. The nerve then passes forwards on the upper aspect of the mylohyoid muscle and lateral to the muscle. The lingual nerve then passes laterally and hooks below the . Here it gives branches to the mucous membrane of the floor of the mouth and the gingivae. At the anterior border of the hyoglossus muscle,

4 | P a g e the lingual nerve enters the substance of the tongue where it distributes branches of the common sensation to the mucous membrane of its anterior two thirds. The fibres of the chorda tympani are of two types. The majority of the fibers are sensory, with cell bodies in the ; they are distributed with the lingual nerve and sub serve taste sensibility in the anterior two thirds of a tongue, excluding circumvallate papillae. The others are preganglionic parasympathetic fibres, which relay in the . The postganglionic fibres are secretomotor to the submandibular and sublingual glands.

Clinical Considerations: Damage of the sensory fibers that run in VIII leads to disturbances in sensation in its region of supply. This is very broad, but during a routine examination the test is usually confined to the skin over the chin () and side of the cheek (buccal nerve). General sensation to the front of the tongue (lingual nerve) may also be tested. Obviously, a thorough neurological examination can involve tests over other regions (e.g., , ). Damage to the motor fibers within VIII leads to severe disturbances in chewing. Wasting of the temporalis and masseter can be seen. There is also an obvious symptom due to paralysis of the lateral pterygoid. As we know, this muscle is the main depressor of the mandible. When both lateral pterygoids work properly, the moves straight down during voluntary opening of the mouth. If only the right lateral pterygoid is working the right side of the jaw will be pulled forward during opening and the chin will deviate to the left. If only the left lateral pterygoid is working, the chin deviates to the right upon opening of the mouth.

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Tests for strength of the temporalis, masseter, and pterygoids are made in all routine examinations. The examiner places one hand over the left temporalis and the other hand over the right temporalis and then asks the patient to clench his or her teeth. An assessment is made about the degree to which one side may be contracting less strongly than the other. The test is repeated with the examiner's fingers placed over each masseter. If the patient has a complete molar dentition, a tongue depressor may be placed sideways in the mouth between the upper and lower teeth. The patient is asked to bite down and relax. The examiner removes the tongue depressor and assesses if the impressions made by the teeth are equally deep on both right and left sides. The lateral pterygoid, medial pterygoid, and superficial masseter, when acting together on one side, protract that side and cause the jaw to deviate toward the opposite side. The left protractors push the chin toward the right; the right protractors push the chin to the left. If the examiner places a hand on the right side of the chin and attempts to push the jaw to the left, the patient must use the left protractors to resist this. If the examiner places a hand on the left side of the chin and attempts to push the jaw to the right, the right muscles must be used to resist this. By asking the patient to resist such pushes on the jaw, an assessment of strength of the jaw protractors on one side compared with those on the other may be made.

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