The fifth cranial nerve is known as the trigeminal nerve and has 3 branches which are the ophthalmic, maxillary, and mandibular. The third branch is called the mandibular nerve (V3). It is the largest of the 3 branches and carries both afferent and efferent fibers. The first 2 branches of the trigeminal nerve carry only afferent fibers. The mandibular nerve innervates the lower face and the mandible, including the teeth, the temporomandibular joint, and the mucous membrane of the mouth and the anterior two-thirds of the tongue, the mastication muscles, and some smaller muscles.[1][2][3]

From the brain stem, the mandibular branch arises from 3 nuclei (mesencephalic, principal sensory and spinal) and gives rise to the sensory root and one motor nucleus gives rise to the motor root of the nerve. The motor root runs along the floor or the trigeminal cave and joins the larger sensory root before leaving the cranium base as the mandibular branch of the trigeminal nerve through the foramen ovale in the sphenoid bone and enters the infratemporal fossa. Near the skull base, the main trunk immediately gives off the sensory meningeal branch and motor muscular branches to the medial pterygoid, tensor tympani, and tensor veli palatini. After that, it divides into 2 trunks: smaller anterior and larger posterior. The smaller anterior trunk carries mostly efferent fibers that supply the temporalis, masseter and lateral pterygoid muscles, and it also carries afferent fibers that form the buccal nerve. The larger posterior trunk gives off the auriculotemporal nerve which wraps around the medial meningeal artery and supplies sensory innervation to the cutaneous tissue around the auricula and temporal regions. The larger posterior trunk then divides into 2 main splits, lingual and inferior alveolar. The lingual nerve supplies sensory innervation to the anterior of the tongue which does not include taste. The inferior alveolar nerve supplies motor innervations to the mylohyoid and anterior belly of digastric muscles and sensory innervation to the teeth and mucoperiosteum of mandibular teeth, as well as sensory to the chin and lower lip.

The trigeminal nerve is derived from the first pharyngeal arch. The musculature of the first pharyngeal arch includes the muscles of mastication, anterior belly of digastric, mylohyoid, tensor tympani, and tensor veli palatini muscles. The trigeminal nerve was studied by following Xenopus laevis embryos. The development of the mandibular nerve is similar to that of the ophthalmic and maxillary branches. The development follows in 3 stages.

First, a pioneer neurite emerges and a nerve forms as other, later neurites fasciculate with this. Upon reaching the inside surface of the cement gland, the neurites separate and penetrate holes in the basal lamina. Finally, the neurites grow between the cells they will innervate and form free nerve endings.

The mandibular nerve receives its blood supply from various tributaries throughout its course in the body. Three major arteries supply blood to the trigeminal nerve root: a superolateral branch of the basilar artery, a peduncular cerebellar branch of the anterior inferior cerebellar artery, and the trigeminocerebellar artery. The blood supply to the muscles of mastication is via branches of the maxillary artery. The trigeminal artery is a critical potential conduit between the basilar and carotid arteries and follows the course of the trigeminal nerve. The trigeminal artery most commonly arises from the superolateral pontine branch of the basilar artery and from the peduncular cerebellar branch of the anterior inferior cerebellar artery. The number of trigeminal arteries ranges from two to six, with diameters ranging from one hundred to five hundred and ten micrometers.

Afferently, the mandibular nerve serves the lower face and its cutaneous tissues between the lower lip and the base of the mandible. Efferently, the mandibular branch serves the muscles of mastication, the tensor veli palatini - muscle of the soft palate, and tensor veli tympani of the middle ear along with the mylohyoid and anterior digastric muscles.

The meningeal branch of the nerve provides sensory supply to the dura mater of the middle cranial fossa and a part of the anterior cranial fossa. The nerve to tensor veli palatini supplies motor innervation to the tensor veli palatini which tenses and elevates the soft palate to close and prevent food from entering the nasopharyngeal space during swallowing. The nerve to tensor tympani provides motor innervation to its respective muscle in the middle ear space which is responsible for dampening the noise produced by chewing, which helps to prevent ear ossicle damage. The auriculotemporal nerve provides sensory innervation to the temporomandibular joint (branches of temporalis and masseter nerve also provide sensory innervation to the temporomandibular joint). The buccal nerve branch provides sensory innervation to the lower buccal gingiva, lower buccal sulcus, and the mucosa of the cheeks.

The following branches of the mandibular nerve efferently serve the muscles of mastication which include the medial and lateral pterygoids, masseter, and the temporalis. The nerve to medial pterygoid provides innervation to its respective muscle which is responsible for the elevation of the mandible (closes the jaw). The nerve to temporalis provides innervation to the temporalis muscle which is responsible for elevation and retrusion of the mandible (closes and retracts the jaw). The masseteric nerve supplies the masseter muscle which elevates and protrudes the jaw. The nerve to lateral pterygoid provides innervation to the lateral pterygoid muscle which depresses the mandible.[4][5][6]

The posterior trunk of the mandibular nerve splits into two branches known as the inferior alveolar nerve and the lingual nerve. The inferior alveolar nerve carries both motor and sensory fibers and travels along the medial aspect of the lateral pterygoid muscle. Before entering the mandibular foramen, it gives rise to branches that provide motor innervation to the mylohyoid and anterior belly of digastric muscle which is responsible for elevating the hyoid and complex movements of the jaw (speaking, swallowing, chewing, and breathing).  Once the nerve enters the mandibular foramen, it provides innervation to the mandibular teeth and the lower alveolar ridge. A branch of the nerve exits via the mental foramen to become the mental nerve which provides sensory innervation to the dermis of the chin and lower lip and the remaining nerve fibers continue anteriorly to provides innervation to the canines and incisors. The lingual nerve innervated the anterior two-thirds of the tongue and mucous membrane for sense but does not innervate taste fibers.[7][8]