Trigeminal Nuclei: Central and Peripheral Connections

The mandibular nerve (V3) is the largest branch of the trigeminal nerve and consists of a large sensory root and a small trigeminal motor root. The sensory portion innervates the cheeks, chin and lower lip, gums, inferior teeth, mucous membranes of the mouth, anterior two thirds of the tongue, side of the head, lower jaw, anterior wall of the external auditory meatus, external wall of the tympanic membrane, and the temporomandibular joint. The sensory and motor parts leave the skull through the foramen ovale and unite to form a short nerve that lies between the lateral pterygoid and tensor veli palatine muscles, anterior to the middle meningeal artery. The small otic ganglion closely adheres to the medial side of the nerve. Just below the foramen, the mandibular nerve gives off a meningeal branch (nervus spinosus). It supplies the meninges of the middle and anterior cranial fossae and calvaria, and the mucous membrane of the mastoid air cells. The nerve to the medial pterygoid muscle sends fibers through the otic ganglia without relay to supply the tensor veli palatine and tensor tympani muscles. The main mandibular nerve divides into a small anterior and a larger posterior part. The anterior part contains primarily motor fibers through the nerve to the lateral pterygoid and two or three deep temporal nerves that innervate the temporalis muscle. The anterior portion has one sensory branch, the buccal nerve, which innervates the areas of skin overlying the buccinators muscle and the mucous membranes beneath. The posterior part of the mandibular nerve is primarily sensory and divides into the auriculotemporal, lingual, and inferior alveolar nerves. The mylohyoid muscle and the anterior belly of the digastrics are supplied by a few motor fibers that are distributed in the mylohyoid branch of the inferior alveolar nerve. At its origin, the auriculotemporal nerve divides in two around the middle meningeal artery. It ends in the superficial temporal branches that supply the skin and fascia of the temple and adjacent areas of the scalp. The auriculotemporal nerve also gives branches to the temporomandibular joint, the external acoustic meatus, and the tympanic membrane, and an anterior auricular branch to the skin of the tragus and part of the helix. It supplies filaments containing secretomotor and vasomotor fibers to the parotid gland, which reach the nerve through the otic ganglion. Sensation to the anterior two thirds of the tongue and floor of the mouth is carried by the lingual nerve. It is joined near its origin by the chorda tympani, a branch of the facial nerve, which conveys taste from the part of the tongue anterior to the V-shaped sulcus terminalis. The lingual nerve supplies the mucous membrane of the anterior two thirds of the tongue, lower part of the isthmus of the fauces, and the floor of the mouth, including the lingual surfaces of the lower gums. The branches communicate with the terminal branches of the glossopharyngeal and hypoglossal nerves. The inferior alveolar nerve descends behind the lingual nerve. It gives off its only motor branch, the mylohyoid nerve, before entering the canal. The mylohyoid nerve supplies the mylohyoid muscle and the anterior belly of the digastric. The other branches of the inferior alveolar nerve are the mental nerve and inferior dental and gingival rami, which arise from the nerve as it passes through the mandibular canal. The latter are delicate nerves that unite to form the inferior dental plexuses supplying the lower teeth and gums. They may be joined by branches of the buccal and lingual nerves or by filaments from nerves supplying the muscles attached to the mandible. These branches may carry sensory fibers, which explains why blocking the inferior alveolar nerve alone does not always anesthetize the lower teeth.

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