Anatomy of the Mandibular Nerves

Anatomy of the Mandibular Nerves

The mandibular nerve (MN) is one of the branches of the trigeminal nerve (CNV). The trigeminal nerve gives rise to three branches; the ophthalmic nerve (CNV1), the maxillary nerve (CNV2) and the mandibular nerve (CNV3). MN processes communications betweenthe brain and the body, in which afferent and efferent fibres are carried out. The MN innervates the lower face including the mandible and teeth as well asthe anterior two-thirds of the tongue, lower lip, mastication muscles and some smaller muscles (Ghatak, Helwany & Ginglen 2022).

Figure 1. Distribution of the trigeminal nerve with its terminal branches.

The MN, which is essential for mouth movement, branches off from the CNV and connects to the lower jaw. It has both motor and sensory functions in the skull and interacts with fibres of other cranial nerves. It is the largest of the three branches of the fifth cranial nerve, the CNV. The CNV is important for facial sensation, biting and chewing movements (Dellwo 2022).

The trigeminal ganglion of Gasser is the source of theMN which exits the skull via the foramen ovale. It then proceeds to split up into two divisions, anterior and posterior followed by a subdivision of smaller branches that supply blood to the facial structures (Vaskovi 2022).This can be seen in figure 2. The anterior division bifurcate and gives rise to the masticatory muscle motor branches (masseteric nerve, deep temporal nerves and nerve to lateral pterygoid). The buccal nerve is also another sensory branch that stems from the anterior division. This nerve runs within the lateral pterygoid heads, while crossing the primary and anastomoses alongside the facial nerves in which it supplies the surrounding skin of the cheek as well as buccal mucosa (Vaskovi 2022).

A division of the masseteric nerve provides innervation for the temporomandibular joint as it travels anteriorly. The masseter, also serving to support, is punctured as it travels posteriorly to the tissue of the temporalis muscle. One anterior branch and another posterior branch make up the deep temporal nerves (Vaskovi 2022). The anterior branch typically arises from the buccal nerve, whereas the posterior branch releases from the MN's anterior section; the temporalis muscle is innervated by each of them. The lateral pterygoid muscle is derived from and innervated by the anterior trunk (Vaskovi2022).

In figure 2, the posterior division branches off three main sensory nerves which includes the auriculotemporal, lingual, and inferior alveolar nerves. The auriculotemporal nerve consists of two roots that surround the middle meningeal artery from a loop (Vaskovi2022). The auriculotemporal nerve emerges from the union of the two roots which lead to a single trunk that runs deep towards the lateral pterygoid muscle, as well as the temporomandibular joint (Vaskovi 2022).

The superficial branches that run throughout the tragus and the surrounding area of the auricle are produced by the auriculotemporal nerve as it crosses the zygomatic joint. The nerve also obtains several branches that branch off and enter the facial nerve, giving the mylohyoid and digastric muscles within the anterior belly of the stomach. The chords tympani are joined by the lingual nerve as it travels deep towards the lateral pterygoid. It flows past the medial pterygoid and proceeds the mandibular ramus The lingual nerve also supplies the surface of the oral cavity, mandibular gingiva as well as two-thirds of the tongue (Vaskovi 2022).

The inferior alveolar nerves cross the medial facet of the lateral pterygoid as well as producing the motor branches to the mylohyoid and anterior surface of the gastrocnemius muscles. The nerve proceeds to enter the mandibular foramen in which the lower teeth and alveolar ridges are supplied by it as it passes through (Vaskovi2022). Following its anterior passage, the nerve turns into the mental nerve as it leaves the mandible via the mental foramen. Moreover, this nerve sensitises the skin that covers the chin (Vaskovi2022).

Figure 2. Distribution of the mandibular nerve.

The MN is a nerve that provides sensory and motor fibres that are necessary for movement and senses. The mandibular branch of CNV gives rise to sensory fibres which provide innervation to the anterior two-thirds of the tongue, inferior set of teeth and gingiva, and the chin and lower lip (Little 2018). The main nerve which is responsible for conduction of motor axons towards muscles of the head and neck is the MN. The CNV consists of motor roots which joins distal sensors towards the trigeminal ganglion eventually leading its axons into the muscles of mastication. The muscles of mastication mainly include the temporalis, the medial and lateral pterygoids and the masseter nerves (Little 2018).

Many other processes occur for the innervation of the muscles allowing for the process of mastication including the mylohyoid (M), anterior belly of digastric (ABD), tensor palli palatini (TPP) and tensor tympani (TT). The M and ABD allows the suprahyoid muscle to carry out swallowing, TPP allows elevation of the soft palate which prevents regurgitation into the nasopharynx and TT dampens sound during chewing as its stability occurs in the middle ear via the malleus bone (Little 2018).

The MN is one of the largest divisions found along the base of the cranium (Rodella et al. 2011). Regarding anatomical variations, the posterior division of the MN and the subdivisions of the inferior alveolar nerve have many deviations. This includes the masseter, auriculotemporal and the lingual branches (Sissere et al. 2009). The masseter plays a significant role for the function of the mandible as its primary responsibility is to elevate and protract the mandible. The motor innervation of the masseter is accompanied by the anterior division of the mandibular division through the CNV (Corcoran & Goldman 2022).

The innervation of the auriculotemporal branch occurs behind the temporomandibular joint and has connections with the inferior alveolar nerve. The main function of this nerve is to supply sensation to the tragus and the helical crus through somatic afferent fibers; with the fibers originating from the trigeminal nucleus of the pons and travelling through the foramen ovale. The superior root of the auriculotemporal nerve also provides sensations throughout the temple, the posterior temporomandibular joint, and the tympanic membrane (Greenberg & Breiner 2021). The lingual nerve is located below the lateral pterygoid muscle and medially faces the front of the inferior alveolar nerve in the mandible. Sensory and somatic afferent innervations are conductedby the lingual nerve via the frontal two-thirds of the tongue,where it can supply mucous membrane production (Alali, Mangat & Caminiti 2018).

In conclusion, this review highlights the branching pathways of the MN along with its physiological functions and anatomical variations.

References:

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