Anatomy, Head and Neck, Mylohyoid Nerve

The trigeminal nerve (CN V) is responsible for sensory innervation of the face. The trigeminal nerve splits off into three main branches. The three branches that originate from the trigeminal nerve are the ophthalmic nerve (CN V1), the maxillary nerve (CN V2), and the mandibular nerve (CN V3). These nerves will provide sensory innervation to their respective territories. The trigeminal nerve also provides motor innervation to the muscles used in mastication. The maxillary nerve and the mandibular nerve will provide motor innervation to the muscles used for mastication. Each muscle that is involved in mastication receives a nerve that branches from the maxillary nerve or the mandibular nerve. For example, the mylohyoid muscle contributes to chewing, speaking, and swallowing. This muscle receives innervation from a nerve called the mylohyoid nerve. The mylohyoid nerve is one of the branches of the inferior alveolar nerve (branch of the mandibular nerve).

The mylohyoid nerve is a branch from the inferior alveolar nerve. The inferior alveolar nerve originates from the mandibular branch of the trigeminal nerve. The branching of the inferior alveolar nerve into the mylohyoid nerve occurs before the inferior alveolar nerve enters the mandibular foramen. Once the mylohyoid nerve branches, it will descend on the medial side of the mandibular ramus. The mylohyoid nerve will perforate through the sphenomandibular ligament to enter the mylohyoid groove and continues to descend towards the mylohyoid muscle. The mylohyoid nerve travels closely with the medial division of the submandibular glands, ultimately settling between the mylohyoid muscle and the anterior muscle belly of the digastric muscle. The anatomical position of the mylohyoid nerve is inferolateral to the mylohyoid muscle but superior to the anterior muscle belly of the digastric muscle.[1][2][3]

The mylohyoid nerve's function is to provide motor innervation to the mylohyoid muscle and the anterior muscle belly of the digastric muscle.[1] It also gives off a cutaneous nerve. This cutaneous nerve branch will provide sensory innervation to the inferior aspect of the chin. The mylohyoid nerve also provides sensory nerves to the first molar's mesial root.

During fetal development, the structures in the face and neck form from the brachial apparatus. The brachial apparatus is made up of the brachial clefts, the brachial arches, and the brachial pouches. The brachial arches are responsible for developing the muscles, nerves, and bones. The brachial arches are made up of neural crest cells and mesoderm. The mesoderm will develop into the muscles and some of the bones while the neural crest cells will develop into the peripheral nerves and some of the facial bones. The maxillary nerve and the mandibular nerve branches of the trigeminal nerve are derivatives of the first brachial arch. As the mandibular nerve continues to develop and elongate, it will branch and form the inferior alveolar nerve as one of its branches. The inferior alveolar nerve will branch into the mylohyoid nerve, making the mylohyoid nerve a derivative of neural crest cells in the first brachial arch.

The blood supply to the mylohyoid nerve is predominately from the branches of the external carotid artery. The mylohyoid nerve receives perfusion from different arteries as it descends toward the mylohyoid muscle. The inferior alveolar arteries will perfuse the mylohyoid nerve around the mandible region. Once the mylohyoid nerve reaches the mylohyoid muscle, it will receive that same perfusion as the mylohyoid muscle. The arteries that perfuse the mylohyoid muscle are the mylohyoid branch of the inferior alveolar artery and the submental branches of the facial artery.[1]

The lymphatic drainage of the territory innervated by the mylohyoid nerve gets directed towards the submental lymph nodes and the submandibular lymph nodes. The lymph fluid will eventually drain toward the right lymphatic duct or the thoracic duct. The right lymphatic duct will drain the right side of the face and neck. The left side of the face and neck will drain toward the thoracic duct. The right lymphatic duct and the thoracic duct will drain back into the central circulation.[4]

The mylohyoid nerve is a branch of the inferior alveolar nerve. The inferior alveolar nerve originates from the mandibular branch of the trigeminal nerve. The mylohyoid nerve provides both motor and sensory innervation.[3]