The nerve innervation in the face divides between the facial nerve (cranial nerve VII) and the trigeminal nerve (cranial nerve V). The facial nerve provides the motor innervation to the muscles that participate in facial expression. The trigeminal nerve is the source of sensory innervation to the face. Along with sensory innervation, the trigeminal nerve also provides motor innervation to the muscles used for mastication.
The sensory map of the face can further divide between the three main branches of the trigeminal nerve. The first branch that arises from the trigeminal nerve is the ophthalmic nerve (CN V1). The ophthalmic nerve provides sensory innervation to the eye region and parasympathetic innervation. The second branch of the trigeminal nerve is the maxillary nerve (CN V2). The sensory territory of the maxillary nerve is mainly below the eye extending to the upper lip. The last branch from the trigeminal nerve is the mandibular nerve (CN V3). The mandibular provides motor innervation to the muscles of mastication. The sensory innervation territory of the mandibular nerve correlates with the mandibular bone. These regions include the jawline, lower lip, and chin mainly.
The branches of the trigeminal nerves will further branch into different nerves to provide sensory innervation to their sensory territories; for example, the mandibular nerve branches into the alveolar nerve. The alveolar nerve will travel within the mandible bone and then branches into the mental nerve. The mental nerve will be responsible for providing sensory innervation to the lower lip and the chin region.