The facial nerve is also known as the seventh cranial nerve (CN7). This nerve performs two major functions. It conveys some sensory information from the tongue and the interior of the mouth. Specifically, CN7 serves about two-thirds of the tongue's tip. The nerve extends from the brain stem, at the pons and the medulla. Also, this nerve innervates facial muscles, controlling how to contract and produce facial expressions.
During its course, CN7 splits into several branches. The greater petrosal nerve serves the lacrimal gland (the gland that produces tears) and the nasal cavity, as well sphenoid, frontal, maxillary, and ethmoid sinuses (cavities in the skull). One of the branches provides motor signals to the stapedius muscle, which is situated in the inner ear. The branch called the chorda tympani serves the sublingual glands (a major salivary gland) and the submandibular glands (glands that lie under the floor of the mouth). The chorda tympani also conveys taste sensations from the tip of the tongue.
Most problems involving the facial nerve include paralysis, commonly with Bell's palsy. This condition, as well as other forms of paralysis, is sometimes triggered by a viral infection or complications of Lyme disease.