Discussing The Nerve Supply of The Tongue

All the muscles of the tongue are supplied by the hypoglossal nerve except palatoglossus, which is actually a muscle of the palate. The two sides of the tongue are independent in their nerve supply, so if for example the left hypoglossal nerve is damaged, the muscles on the right can protrude the right half of the tongue but those on the left are paralyzed. Thus, when the patient is asked to protrude the tongue, the tongue will deviate to the left, i.e. to the same side as the lesion.
The sensory innervation of the tongue follows the 2/3rd: 1/3rd ratio. The anterior 2/3rd that develops from the first branchial arch is supplied by a branch of the mandibular division (lingual nerve) for general sensation. This is supplemented by a branch of the nerve of the second arch (facial) in the form of chorda tympani which joins the lingual in the infratemporal fossa and is involved in carrying taste sensation from the anterior 2/3rd. The posterior 1/3rd develops from the third branchial arch and is therefore supplied by the glossopharyngeal nerve both for general and taste sensation. The internal laryngeal branch of the vagus also supplies a small area of the mucosa of the tongue just anterior to the epiglottis. The above-mentioned division of the tongue is a classical description but is only approximate. The vallate papillae although in front of the sulcus terminalis are nevertheless supplied by the glossopharyngeal nerve.