introduction
The fifth cranial nerve, the trigeminal nerve, has three branches which are ocular, maxillary and mandibular. The third branch is called the mandibular nerve (V3). It is the largest of the three departments and carries afferent and efferent fibers. The first two branches of the trigeminal nerve carry only afferent fibers. The mandibular nerve innervates the lower face, including the mandible, lower teeth and oral mucosa, the anterior two-thirds of the tongue, lower lip, temporomandibular joint, masticatory muscles and some minor muscles, the skin of the temporal region and an area of the ear and of the external auditory canal of the abdomen.[1][2][3][4]
structure and function
In the brainstem, the mandibular ramus originates from 3 nuclei (midbrain, main sensory nucleus and spinal nucleus) from where its large sensory root arises. The motor root of the nerve originates from the motor nucleus of the trigeminal nerve, which is located in the tegmentum of the superior region of the pons.[4]. The motor root runs along the trigeminal cavity and empties into the sensory root before exiting the skull through the foramen ovale and entering the infratemporal fossa. The mandibular nerve is the only branch of the trigeminal nerve that contains a motor root.
In the infratemporal fossa, near the base of the skull, the main trunk immediately gives rise to the meningeal sensory branch and motor muscular branches to the medial pterygoid, tensor tympani, and tensor veli palatini muscles. After that, the main trunk splits into two parts: smaller front and larger rear. The lesser anterior trunk contains efferent fibers that supply the temporalis, masseter, and lateral pterygoid muscles, and afferent fibers that supply the buccal nerve. The greater posterior trunk gives off the auriculotemporal nerve, which surrounds the medial meningeal artery and provides sensory innervation to the skin tissue around the pinna and temporal regions. The greater posterior trunk then divides into two main divisions, lingual and inferior alveolar. The lingual nerve provides sensory innervation to the anterior two-thirds of the tasteless tongue. The inferior alveolar nerve supplies motor innervations to the mylohyoid and anterior belly of the digastric muscles, and sensory innervations to the teeth and mucoperiosteum of the mandibular teeth, and sensory innervations to the chin and lower lip.
Embryology
The trigeminal nerve arises from the first pharyngeal arch. The muscles of the first pharyngeal arch include the masticatory muscles, the anterior digastric abdomen, the mylohyoid, the tensor tympani, and the tensor veli palatini. The development of the mandibular nerve resembles that of the ocular and maxillary branches. Development takes place in 3 stages. A pioneer neuritis appears first and a nerve forms, while other, later, neurites fasciculate with it. Upon reaching the inner surface of the cementum gland, the neurites separate and enter holes in the basal lamina. Eventually, neurites grow between the cells they innervate, forming free nerve endings.
blood supply and lymph vessels
Three major arteries supply blood to the trigeminal nerve root: a superolateral branch from the basilar artery, a pedunculated cerebellar branch from the anterior inferior cerebellar artery, and the trigeminocerebellar artery. The blood supply to the masticatory muscles is provided by branches of the maxillary artery. The trigeminal artery is a critical potential conduit between the basilar artery and the carotid artery and follows the path of the trigeminal nerve. The trigeminal artery most commonly arises from the superolateral pons branch of the basilar artery and the pedunculated cerebellar branch of the anterior inferior cerebellar artery. The trigeminal arteries vary in number from two to six, with diameters from one hundred to five hundred and ten micrometers.
Irritate
Afferently, the mandibular nerve supplies the lower half of the face and its cutaneous tissue between the lower lip and the base of the mandible. Efferently, the mandibular ramus serves the muscles of mastication, the tensor veli palatini - muscle of the soft palate, and the 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 part of the anterior cranial fossa. The nerve to the tensor veli palatini provides motor innervation to the tensor veli palatini, which tenses and lifts the soft palate to close it and prevent food from entering the nasopharynx during swallowing. The nerve to the tensor tympani provides motor innervation to its respective muscle in the middle ear cavity, which is responsible for muffling the sounds produced by chewing, preventing damage to the auditory ossicles. The auriculotemporal nerve provides sensory innervation to the temporomandibular joint (branches of the temporal and masseter nerves also provide sensory innervation to the temporomandibular joint). The branch of the buccal nerve supplies sensory supplies to the lower gums of the mouth, the 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, the masseter and temporalis. The medial pterygoid nerve innervates its respective muscle responsible for mandible elevation (jaw closure). The temporal nerve innervates the temporalis muscle, which is responsible for elevating and repressing the mandible (closing and retracting the mandible). The masseter nerve innervates the masseter muscle, which elevates and projects the mandible. The nerve to the lateral pterygoid supplies the lateral pterygoid muscle, which depresses the mandible.[5][6][7]
The posterior trunk of the mandibular nerve divides into two branches known as the inferior alveolar nerve and the lingual nerve. The inferior alveolar nerve carries motor and sensory fibers and runs along the medial side of the lateral pterygoid muscle. Before entering the mandibular foramen, branches arise that provide motor innervation to the mylohyoid and the anterior belly of the digastric muscle, which is responsible for hyoid elevation and complex movements of the mandible (speech, swallowing, chewing, and breathing). Once the nerve enters the mandibular foramen, it innervates the mandibular teeth and the inferior alveolar ridge. A branch of the nerve exits through the mental foramen to become the mental nerve which sensory innervates the dermis of the chin and lower lip, and the remaining nerve fibers continue anteriorly to innervate the canines and incisors. The lingual nerve innervates the anterior two-thirds of the tongue and the sensory mucosa, but does not innervate the taste fibers.[8][9]
physiological variants
One study showed that about 20% of the population has anatomical variations of the trigeminal nerve. All of this is related to the mandibular nerve and its branches, not the ophthalmic or maxillary nerve. Some anatomical variations that have been reported include:
Anatomical Variations of the Inferior Alveolar Nerve
Anatomical variations of the lingual nerve
Anatomical variations of the buccal nerve
Anatomical variations of the auriculotemporal and
Cervical plexus: Additional innervation of the lower jaw region
The inferior alveolar nerve can give rise to several extraosseous branches before entering the mandibular canal and, within the bony canal, it can give rise to several intraosseous branches. The inferior alveolar nerve may also present anatomical differences in its relationship with the maxillary artery.
Quantitative studies were performed to estimate the position of the lingual nerve in relation to the third molar region. Studies report that the mean horizontal distance from the nerve to the lingual plate ranges from 0.58 to 3.45 mm; while the mean vertical distance of the lingual nerve below the alveolar crest ranges from 2.28 to 8.32 mm. This is important for oral surgery, e.g. B. third molar extraction, treatment of mandible lesions, periodontal interventions and excision of neoplastic lesions.
The long buccal nerve may innervate the lower molars by entering the alveolar bone through the retromolar foramina. This could explain the failure of the traditional alveolar nerve block.
The auriculotemporal nerve has been described as having a connection with the inferior alveolar nerve. In regional anesthesia, this impairs the effectiveness of the inferior alveolar nerve.
Additional nerve fibers may arise from the cervical plexus, which also innervate the lower jaw area. The great auricular nerve arises from the cervical plexus, which afferently innervates the mastoid process, parotid gland, and external ear. In cases of third molar extractions in which conventional anesthesia was unsuccessful, anesthesia of the greater auricular nerve has been reported. This suggests that the greater auricular nerve is involved in innervating the mandibular angle and separate nerve infiltration may be required to achieve complete anesthesia of the mandibular region.
Surgical Considerations
The mandibular nerve plays an important role in oral and maxillofacial surgery and anesthesia. A major surgical concern is the location of the infratemporal fossa, where mandibular nerve compression is common. The infratemporal fossa is one of the regions with the most difficult surgical access. In anesthesia, variations of the inferior alveolar nerve are important for surgical and dental practice. Case reports describe anatomical variations of the inferior alveolar nerve that mimic the recurrence of keratocystic odontogenic tumors.
Sympathetic and parasympathetic autonomic nerve fibers travel with different branches of the trigeminal nerve to reach their target organs and tissues.
clinical significance
Due to many physiological variations, it is a common problem that physicians and dentists cannot achieve complete anesthesia of the mandibular nerve. Temporomandibular joint dysfunction (TMD) is caused by a group of disorders that cause pain and joint dysfunction in the temporomandibular joint and the muscles that control jaw movement. Many branches of the mandibular nerve are responsible for controlling jaw movement and dysfunction can lead to TMD. The auriculotemporal nerve can be damaged during temporomandibular joint surgery, which can cause pinna and ear region paresthesia.[10]
Trigeminal neuralgia often occurs with damage to the mandibular ramus and can be treated by cutting the sensory root. Classic trigeminal neuralgia occurs due to vascular compromise of the trigeminal nerve root. Secondary trigeminal neuralgia is based on severe neurological diseases such as multiple sclerosis or tumors with possible involvement of the branches of the mandibular nerve.
Ear pain due to radiation along the auriculotemporal nerve in a patient with tongue cancer was documented. Tensor tonic tympani syndrome causes ear pain, a fluttering sensation, or a feeling of fullness in the ear. Increased tensor tympani activity develops in many people with hyperacusis as part of the startle response to certain sounds.
Figure
The trigeminal nerve, distribution of the maxillary and mandibular nerves; the mandibular ganglion. Contributed by Gray's Anatomy Plates
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