The mandibular nerve is a terminal branch of the trigeminal nerve, along with the maxillary and ophthalmic nerves. As a nerve, it is of vital importance in the head, providing both sensory and motor functions, along with parasympathetic fibres associated with other cranial nerves. In this article, we shall look at the anatomy of the mandibular nerve, exploring its anatomical course, branches, sensory, motor and autonomic functions.
The mandibular nerve is made up of both sensory and motor axons. These axons arise from three sensory nuclei - the mesencephalic, principal sensory and spinal nuclei of the trigeminal nerve - and one motor nucleus - the motor nucleus of the trigeminal nerve. The motor root of the mandibular nerve runs along the floor of the trigeminal cave beneath the ganglion, joining with the sensory root before exiting the cranium via the foramen ovale.
Once the mandibular branch has emerged from the cranium, it courses through the infratemporal fossa, branching into four tributaries which are described below. These branches are responsible for the sensory and motor functions of the nerve, distributing these functions to the lower third of the face, the lower row of teeth and gingiva, and the anterior two thirds of the tongue.
The auriculotemporal branch of the mandibular nerve emerges from the trigeminal nerve as two separate roots: a superior root containing sensory fibres, and an inferior root carrying parasympathetic secretory-motor fibres originating from CNIX to the parotid gland. The two roots converge near the middle meningeal artery, with the secretory-motor fibres travelling to synapse in the otic ganglion, and the sensory fibres passing through the ganglion without synapsing and eventually innervating the anterior part of the auricle, the lateral part of the temple, the anterior external meatus, and the anterior tympanic membrane.
The buccal branch of the mandibular nerve contains only sensory fibres. As with the other branches of the mandibular nerve, it emerges from the mandibular nerve and passes between the two heads of the lateral pterygoid muscle before heading to its target sites. The buccal nerve provides general sensory innervation to the buccal membranes of the mouth (i.e. the cheek) as well as branches to supply the second and third molar teeth, which is vital when performing dental work on those structures.
The inferior alveolar nerve contains both sensory and motor axons, which it carries to and from the respective trigeminal nuclei. It then branches off from the mandibular nerve to give rise to the mylohyoid nerve, a motor nerve to the mylohyoid and anterior digastric muscles. The remaining sensory axons enter the mandibular canal, a narrow tunnel running through the mandible bone. Within this canal, the nerve provides branches to the mandibular teeth. The nerve then emerges from the mental foramen as the mental nerve; this nerve provides sensory innervation to the lower lip and chin.
The lingual nerve branch of the trigeminal nerve carries both general sensory and autonomic fibres, as well as special sensory fibres belonging to the chorda tympani, a branch of the facial nerve (CN VII). The general sensory fibres innervate the anterior two thirds of the tongue, as well as the mucus membrane lining its undersides. The special sensory fibres travel along with the lingual nerve to provide taste to the anterior two thirds of the tongue. The autonomic fibres branch to synapse in the submandibular ganglion, eventually innervating the submandibular and sublingual glands.
In conclusion, the mandibular nerve is an essential branch of the trigeminal nerve. As a complex nerve, it provides both sensory and motor functions, as well as parasympathetic fibres associated with other cranial nerves. It is composed of four branches - the auriculotemporal nerve, the buccal nerve, the inferior alveolar nerve, and the lingual nerve - which are responsible for supplying the lower third of the face, the lower row of teeth and gingiva, and the anterior two thirds of the tongue with their associated sensory and motor functions.
The motor root of the trigeminal nerve (CN V) joins the sensory component distal to the trigeminal ganglion to distribute its axons to the muscles of mastication. These include the masseter, medial and lateral pterygoids, and temporalis. In addition to enabling mastication, the mandibular nerve also innervates muscles involved in several other processes, such as the tensor tympani, which dampens sounds by stabilizing the malleus bone in the middle ear, and the tensor veli palatini, a muscle which helps elevate the soft palate to prevent regurgitation of food and liquids into the nasopharynx. In the suprahyoid region, the mandibular nerve provides motor innervation to the anterior belly of the digastric and mylohyoid muscles, both of which are involved in elevating the hyoid bone during swallowing.
The trigeminal nerve does not have an autonomic nucleus and, as such, does not give rise to any autonomic axons directly. However, all three of its branches take on autonomic fibres of other cranial nerves to provide a passage to their respective targets. The mandibular nerve is particularly associated with parasympathetic secretory-motor fibres from both the facial nerve (CN VII) and the glossopharyngeal nerve (CN IX), respectively.
The chorda tympani nerve, which branches from the facial nerve at the region of the middle ear, carries pre-synaptic parasympathetic fibres that joins the mandibular nerve’s lingual branch before branching to synapse in the submandibular ganglion. These fibres go on to innervate the submandibular and sublingual salivary glands. Autonomic innervation of the parotid gland originates from the glossopharyngeal nerve, however the auriculotemporal nerve transmits the post-synaptic axons from the otic ganglion to the gland, passing through the inferior of the two founding roots of the branch.
The use of local anesthetics in the region of the mandibular nerve, and its tributaries, is a common procedure for dental surgery. The purpose is to remove general sensation from the ipsilateral mandibular row of teeth, in addition to the buccal membranes, chin and jaw. The technique involves injecting the blocking agent into the region of the mandibular nerve from inside the mouth, guided by the second molar tooth. A more specific option is an inferior alveolar nerve block, which allows anesthesia of the inferior row of teeth while sparing the sensory distribution of the rest of the nerve.
Once the mandibular branch has emerged from the cranium, it courses through the infratemporal fossa before branching into four tributaries: the auriculotemporal nerve, buccal nerve, inferior alveolar nerve, and mental nerve.
The auriculotemporal nerve arises from the trigeminal nerve as two roots – the superior root, which comprises sensory fibres, and the inferior root, carrying secretory-motor parasympathetic fibres originating from CN IX to the parotid gland. The two roots converge near the middle meningeal artery, with the secretory-motor fibres running to the otic ganglion to synapse, while the sensory fibres pass through the ganglion without synapsing to eventually innervate the anterior part of the auricle, the lateral part of the temple, the anterior external meatus, and the anterior tympanic membrane.
The buccal branch of the mandibular nerve contains sensory fibres, which are distributed to the buccal membranes of the mouth and the second and third molar teeth. As it emerges from the mandibular nerve, it passes between the two heads of the lateral pterygoid muscle before heading to its target sites.
The inferior alveolar nerve carries both sensory and motor axons to and from the respective trigeminal nuclei. After branching from its parent nerve it gives rise to the mylohyoid nerve, a motor nerve to the mylohyoid and anterior digastric muscles. The remaining sensory axons enter the mandibular canal, a narrow tunnel running through the mandible bone, to provide branches to the mandibular teeth.
The mandibular nerve is one of the four branches of the fifth cranial nerve (CN V). It emerges through the mental foramen as the mental nerve to innervate the lower lip and chin with sensory fibres. In addition to this, it also transmits special sensory and autonomic fibres from the chorda tympani branch of the facial nerve (CN VII) for taste sensation, and autonomic fibres for innervation of the submandibular and sublingual glands. Furthermore, it is the only branch of the trigeminal nerve that is responsible for motor axons to the muscles of the head and neck.
The sensory fibres of the mandibular nerve provide innervation to:
Special sensation to the anterior two thirds of the tongue is provided by the facial nerve. The trigeminal nerve does not have an autonomic nucleus and thus does not provide any autonomic axons directly. However, all three branches of CN V take autonomic fibres of other cranial nerves to provide a passage to their respective targets.
The mandibular nerve is the only branch of CN V that is responsible for motor axons to the muscles of the head and neck. These include the masseter, medial and lateral pterygoids, and the temporalis muscles. The motor root of the trigeminal nerve joins the sensory component distal to the trigeminal ganglion and distributes its axons to the muscles of mastication for various processes, such as dampening of sounds by stabilizing the malleus bone in the middle ear, and elevation of the soft palate to prevent regurgitation of food and liquid into the nasopharynx.
The mandibular nerve is associated with parasympathetic secretory-motor fibres from two other cranial nerves. Pre-synaptic parasympathetic fibres from the chorda tympani nerve of the facial nerve join the lingual branch of the mandibular nerve, before branching to synapse in the submandibular ganglion. These fibres then innervate the submandibular and sublingual salivary glands. Autonomic innervation of the parotid gland originates from CN IX, however the auriculotemporal nerve transmits the post-synaptic axons from the otic ganglion to the gland. They pass through the inferior of the two founding roots of the branch.
The use of local anesthetic in the region of the mandibular nerve and its tributaries is a common procedure used in dental surgery. This technique involves injecting the blocking agent into the region of the mandibular nerve from inside the mouth, guided by the second molar tooth. It is used to remove general sensation from the ipsilateral mandibular row of teeth by blocking the sensory distribution of the nerve, and providing anesthesia of the buccal membranes, chin and jaw. However, a more specific option is available in the form of an inferior alveolar nerve block. This method is used to provide anesthesia of the inferior row of teeth while sparing the other facial nerves. This is achieved by injecting the blocking agent further along the mandibular nerve. Where this option does not provide adequate anesthesia, such as due to the presence of an accessory nerve, a mandibular nerve block is used instead.
