One of the first features of the human body to be noticed by another person is the face. The face is made up of many different muscles, nerves, bones, and organs, and has an intriguing network of motor and sensory innervation. The motor innervation to the muscles located in the face is derived mainly from the facial nerve (CN VII) and trigeminal nerve (CN V). The facial nerve provides innervation to the muscles that are involved in creating facial expressions, whereas the trigeminal nerve innervates the muscles used in mastication.

The sensory innervation of the face comes from the trigeminal nerve. The trigeminal nerve subdivides into three main branches that split the face into three territories. The first branch from the trigeminal nerve is the ophthalmic nerve (CN V1). The ophthalmic nerve provides innervation to the forehead, eyes, and nose. The second branch of the trigeminal nerve is the maxillary nerve (CN V2). The maxillary nerve's sensory innervation follows the maxilla bone. The sensory territory of the maxillary nerve will be the cheeks and the upper lip mainly. The last branch from the trigeminal nerve is the mandibular nerve (CN V3). The mandibular nerve is responsible for providing sensory innervation to the regions that correspond to the mandible. These regions are the jawline, chin, and lower lip.

The branches of the trigeminal nerve will further divide into smaller nerve branches to optimally provide sensory innervation to their respective territories. For example, the maxillary nerve will branch into the superior alveolar nerves. Another example is the mandibular nerve branching into the inferior alveolar nerve. The inferior alveolar nerve will be responsible for sensory innervation to the cheek, lips, chin, teeth, and gingivae. 

The sensory territories for the alveolar nerves divide between the superior alveolar nerves and the inferior alveolar nerves. The superior alveolar nerves will come from the branching of the maxillary nerve. The maxillary nerve will branch into the three superior alveolar nerves before it exits the infraorbital foramen. The superior alveolar nerves are named based on their anatomical location. The first branch is the anterior superior alveolar nerve. The anterior superior alveolar nerve travels toward the maxillary sinus. The sensory innervation of the anterior superior alveolar nerve includes the premolars (canine teeth and incisor teeth), maxillary sinus, and inferior meatus. The second branch of the maxillary nerve is the middle superior alveolar nerve. The middle superior alveolar nerve is responsible for providing addition sensory innervation to the sinuses and the maxillary premolar teeth. The third branch of the maxillary nerve is the posterior superior alveolar nerve. The posterior alveolar nerve provides sensory innervation to the cheeks, maxillary sinus and the gingivae. All of the alveolar nerve branches from the maxillary nerve provide sensory innervation to the gingivae and sinuses. These superior alveolar nerves have overlaps in their sensory territory innervation with one another. This provides collateral sensory innervation via a dental nerve plexus.[1]

The inferior alveolar nerve comes from a different branch of the trigeminal nerve. The inferior alveolar nerve is a mandibular nerve branch. The inferior alveolar nerve is responsible for sensory innervation to the gingivae on the lower jaw. The inferior alveolar nerve also branches into the mylohyoid nerve and the mental nerve. As the inferior alveolar nerve descends the mandible, it will branch into the mylohyoid nerve to provide motor innervation to the mylohyoid muscle and the anterior belly of the digastric muscle.[2] The inferior alveolar nerve will then travel in the mandibular foramen until it reaches the mental foramen. Once at the mental foramen, the inferior alveolar nerve exits and becomes the mental nerve. The mental nerve is responsible for innervating the chin, lower lip, and the gingivae.[3]

During embryology, the development of peripheral nerves derives from neural crest cells. The development of the structures in the face originates from the brachial apparatus. The brachial arch is made up of mesoderm and neural crest cells. The brachial arch will form the muscles, nerves, and bones in the face and neck. The first brachial arch will develop the first two branches of the trigeminal nerve. The maxillary nerve and the mandibular nerve and their innervation territories will form from the first brachial arch. As the face develops the maxillary nerve and mandibular nerve will branch into their respective alveolar nerves, which means the alveolar nerves are derivatives of neural crest cells.

The proximal blood supply to the maxillary nerve and the mandibular nerve at the region of the pons is the anterior inferior cerebellar arteries.[3] The distal blood supply to the maxillary, the mandibular nerve, and their nerve branches are from the external carotid artery. The external carotid artery is responsible for the perfusion of the external head and face. The distal blood supply also provides perfusion to the alveolar nerves. The blood supply to the trigeminal nerve will be from the basilar artery, cerebellar arteries, and the vertebral arteries.[4] 

The lymphatic drainage of the alveolar nerves and their sensory territories is toward the submental lymph nodes, the submandibular lymph nodes, and the preauricular lymph nodes. The lymph fluid will eventually be drained back into the right lymphatic duct and the thoracic duct. The right side of the face will drain into the right lymphatic duct, and the left side of the face will empty into the thoracic duct. Finally, the lymph in the right lymphatic duct and the thoracic duct will drain back to the central circulation.

The alveolar nerves separate into the superior alveolar nerves and the inferior alveolar nerves. The superior alveolar nerves originate from the maxillary branch of the trigeminal nerve. The superior alveolar nerves divide into the anterior, middle, and posterior superior alveolar nerves. While the inferior alveolar nerve originates from the maxillary branch of the trigeminal nerve, the alveolar nerve will branch into the mental nerve. All of these alveolar nerves and their subdivisions will contribute to sensory innervation to the face and mouth.