Of the 12 cranial nerves that exit from the brain through openings in the skull, five serve functions having to do with the mouth. Some of these are sensory nerves, which allow the brain to detect sensation in and around the mouth. Some are motor nerves, which send impulses from the brain that tell muscles to move. Other nerves have special functions such as detecting taste or regulating the salivary glands.
Trigeminal Nerve
The University of Michigan Medical School states that the trigeminal nerve---cranial nerve V---has three branches: the ophthalmic, mandibular and maxillary. Two of these branches, the mandibular and maxillary, are related to the mouth. The maxillary branch is a sensory nerve that detects sensations in the sinuses, the palate and the upper lip.
The mandibular branch has both sensory and motor functions. It supplies motor nerve impulses to the muscles of mastication, which aid in chewing. The sensory component of the mandibular branch detects feelings in areas of the jaw, mouth and tongue.
Facial Nerve
The facial nerve is also known as cranial nerve VII. Yale University states that the facial nerve serves both motor and sensory functions and is responsible for supplying impulses to the glands in the mouth as well as the mucus membranes of the palate.
The facial nerve supplies the muscles of facial expression. Its sensory component serves the ear area, but not the mouth.
Additionally, the facial nerve has chemoreceptors, special nerve endings that enable the detection of taste from the tip of the tongue and along the front two-thirds of its length.
Glossopharyngeal Nerve
The glossopharyngeal nerve, cranial nerve IX, supplies taste sensory functions to the rear one-third of the tongue , which is not served by the facial nerve. It supplies motor function to a single muscle, the stylopharyngeus, which opens up the pharynx to allow food to pass through when swallowing. It supplies the largest salivary gland, which is called the parotid gland, and is located in the cheeks. Its sensory functions include detecting sensation in the tonsils and pharynx.
Vagus Nerve
The vagus nerve is cranial nerve X. It detects taste from the root of the tongue and the epiglottis. The vagus nerve supplies motor impulses to the soft palate, pharynx and larynx as well as one of the tongue muscles, the palatoglossus, which elevates the rear of the tongue and aids in swallowing.
Hypoglossus
The last cranial nerve, the hypoglossal nerve, is also known as cranial nerve XII. This nerve functions solely to provide motor impulses. The hypoglossal nerve serves all of the tongue muscles except the palatoglossus.
