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lecture 5 د. احمد فاضل القيسي THE MANDIBULAR NERVE

This is the largest division of the trigeminal nerve and is the only one to contain motor as well as sensory fibers. Developmentally, it is the nerve of the first branchial arch and is thus responsible for supplying structures derived from it.

Its Sensory fibers supply1. the mandibular teeth and their supporting structures, 2. the mucosa of the anterior two-thirds of the tongue and the

floor of the mouth.3. the skin of the lower part of the face (including the lower lip)

and parts of the temporal region and auricle.

Its motor fibers supply 1. the four muscles of mastication 2. the mylohyoid, anterior belly of digastric,3. tensor veli palatini and tensor tympani muscles.

The mandibular nerve is formed in the infratemporal fossa by the union of the sensory and motor roots immediately after they leave the skull at the foramen ovale. Within the foramen ovale, the motor

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root (or roots) lie posteromedially to the sensory root and these roots are accompanied by emissary veins, the lesser petrosal nerve and the accessory meningeal artery. As the mandibular nerve leaves the foramen ovale, it lies on the tensor veli palatini muscle and is covered laterally by the upper head of the lateral pterygoid muscle (slightly anterior to the neck of the mandible).

BRANCHESMain trunk• Meningeal branch (nervus spinosus)• Nerve to medial pterygoid

Anterior trunk:Masseteric nerveDeep temporal nervesNerve to lateral pterygoidBuccal nerve

Posterior trunk:Auriculotemporal nerveLingual nerveInferior alveolar nerve

1. The meningeal branch (nervus spinosus):It is a ‘recurrent nerve’ as it runs back into the middle cranial fossa through the foramen spinosum. It supplies the dura mater lining the middle and anterior cranial fossae and the mucosa of the mastoid antrum and mastoid air cells.

2. The nerve to the medial pterygoid muscle: This enters the deep surface of the muscle and also gives branches that pass uninterrupted through the otic ganglion to supply the tensor tympani and tensor veli palatini muscles.

3. The masseteric nerveThis is usually the first branch of the anterior trunk of the mandibular nerve. It passes above the upper border of the lateral pterygoid muscle and then crosses the mandibular notch to be distributed into the masseter muscle. It also gives an articular branch to the temporomandibular joint

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4. The deep temporal nervesThese nerves also pass above the lateral pterygoid muscle. Anterior middle and posterior deep temporal nerves may be recognized.

5. The nerve to the lateral pterygoid muscleThis may arise separately or may run with the buccal nerve before entering the deep surface of the lateral pterygoid muscle.

6. The buccal branch of the mandibular nerveThis is the only sensory branch of the anterior trunk. It lies on the lateral surface of the buccinator muscle and gives branches to the skin of the cheek before piercing the buccinator to supply its lining mucosa, the buccal sulcus and the buccal gingiva related to the mandibular molar and premolar teeth. It may also carry secretomotor fibres to minor salivary glands in the buccal mucosa. The buccal branch of the mandibular nerve may anastomose with the buccal branches of the facial nerve.

7. The auriculotemporal nerveThis is the first branch of the posterior trunk of the mandibular nerve. It is essentially sensory but it also distributes autonomic fibers to the parotid gland derived from the otic ganglion. It usually arises as two roots (approx. 75% of cases) that encircle the middle meningeal artery and unite behind the artery. The nerve then runs backwards under the lateral pterygoid muscle to lie beneath the mandibular condyle (between the condyle and the sphenomandibular ligament).On entering the parotid region, it turns to emerge superficially between the temporomandibular joint and the external acoustic meatus. From the upper surface of the parotid gland, the auriculotemporal nerve ascends on the side of the head with the superficial temporal vessels, passing over the posterior part of the zygomatic arch. It gives several branches along its course:

Ganglionic branches which communicate with the otic ganglion.

Articular branches which enter the posterior part of the temporomandibular joint

Parotid branches which convey parasympathetic secretomotor fibers and sympathetic fibers to the parotid gland; these fibres are related to the otic ganglion. Sensory fibers

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from the auriculotemporal nerve supply the gland (with the exception of the capsule, which is innervated by the great auricular nerve).

Auricular branches (usually two) which supply the tragus and crus of the helix of the auricle, part of the external acoustic meatus, and the outer (lateral) surface of the tympanic membrane.

Superficial temporal branches which are cutaneous nerves supplying part of the skin of the temple.

8. The lingual nerve.It is essentially a sensory nerve but, following union with the chorda tympani branch of the facial nerve, it also contains parasympathetic fibres. Initially, the nerve lies on the tensor veli palatini muscle deep to the lateral pterygoid muscle. Here, the chorda tympani nerve joins the posterior surface of the lingual nerve.The lingual nerve curves downwards and forwards in the space between the ramus of the mandible and the medial pterygoid muscle .At this level, it lies anterior to, and slightly deeper than, the inferior alveolar nerve. The lingual nerve then leaves the infratemporal fossa, passing downwards and forwards to lie close to the lingual alveolar plate of the mandibular third molar. Before curving forwards into the tongue, the nerve is found above the origin of the mylohyoid muscle and lateral to the hyoglossus muscle.The close relationship of the lingual nerve to the third molar tooth makes the nerve susceptible to damage during removal of the tooth. In addition, in about one in seven cases, the lingual nerve is actually located above the lingual bony plate in the third molar region and is liable to damage during surgery.The lingual nerve supplies the mucosa covering the anterior two-thirds of the dorsum of the tongue, the ventral surface of the tongue, the floor of the mouth and the lingual gingivae of the mandibular teeth.

The chorda tympani fibers of the facial nerve travelling with the lingual nerve are of two types: sensory and parasympathetic. The sensory fibers are associated with taste for the anterior two-thirds of the dorsum of the tongue. The parasympathetic fibers are preganglionic fibers that pass to the submandibular ganglion. Postganglionic fibers are distributed to the submandibular and sublingual salivary glands.

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9. The inferior alveolar nerve This is the largest branch of the mandibular division of the trigeminal nerve. It is the third branch of the posterior trunk of the mandibular nerve. Although it is essentially a sensory nerve, it also carries motor fibers which are given off as the mylohyoid nerve. Indeed, the mylohyoid nerve contains all the motor fibers of the posterior trunk of the mandibular nerve. The inferior alveolar nerve descends deep to the lateral pterygoid muscle, posterior to the lingual nerve in the pterygoid hiatus. Here, it is crossed by the maxillary artery. On emerging at the inferior border of the muscle, it passes between the sphenomandibular ligament and the ramus of the mandible to enter the mandibular foramen. It is accompanied in its course by inferior alveolar blood vessels.The mylohyoid nerve is given off just before the mandibular foramen. It pierces the sphenomandibular ligament and runs in a groove (the mylohyoid groove) which lies immediately below the mandibular foramen. The mylohyoid nerve supplies the mylohyoid muscle and the anterior belly of the digastric. The mylohyoid nerve may also contain sensory fibers that supply the skin of the chin and medial parts of the submandibular triangle in the suprahyoid region.

The main distribution of the inferior alveolar nerve is to the mandibular teeth and their supporting structures, there being molar and incisive branches. The mental nerve is a cutaneous branch that supplies the skin of the chin and the lower lip. Itarises within the mandible in the premolar region, but soon exits onto the face via the mental foramen.

THE OTIC GANGLION:This parasympathetic ganglion lies immediately below the foramen ovale on the medial surface of the main trunk of the mandibular nerve. It is concerned primarily with supplying the parotid gland. Like other parasympathetic ganglia in the head, three types of fibers are associated with it: parasympathetic, sympathetic and sensory fibers. However, only the parasympathetic fibers synapse in the ganglion. The preganglionic parasympathetic fibers originate from the inferior salivatory nucleus in the brainstem. The fibers pass out in the glossopharyngeal nerve, appearing as the lesser (superficial) petrosal nerve from the tympanic plexus in the middle ear cavity. The lesser petrosal nerve reaches the otic ganglion by a complex

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course. Passing through the petrous part of the temporal bone, the lesser petrosal nerve comes to lie in the floor of the middle cranial fossa. Here, it is lateral to thegreater (superficial) petrosal branch of the facial nerve. The lesser petrosal nerve usually enters the infratemporal fossa through the foramen ovale to join the otic ganglion. On occasion, the lesser petrosal nerve passes through the sphenopetrosalfissure. The sympathetic root of the otic ganglion is derived from postganglionic fibers from the superior cervical ganglion.They are said to reach the otic ganglion from the plexus on the middle meningeal artery. Other descriptions have it that the sympathetic root arises from the deep petrosal nerve or directly from the internal carotid plexus. The sensory root is derived from the auriculotemporal nerve. The postganglionic parasympathetic fibers (with sympathetic and sensory components) reach the parotid gland by way of the auriculotemporal nerve. Parasympathetic fibers may also innervate the minor salivary glands in the cheek, passing with the buccal branch of the mandibular nerve.The innervation of tensor veli palatini and tensor tympani is derived from the nerve to the medial pterygoid by a branch that passes through the otic ganglion.

Clinical significance:Lesions of mandibular division of trigeminal nerve will cause unilateralparalysis of muscles of mastication followed by atrophy; results in a sunken-inappearance along ramus of mandible and above the zygomatic arch.

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