Motor innervation of the tongue is provided by the hypoglossal nerve (cranial nerve CN XII) with the exception of the palatoglossus muscle, which is innervated by the vagus nerve (CN X).
General sensory innervation of the tongue (including touch, pain, pressure, and temperature sensation) is provided by:
Anterior 2/3 of the tongue: mandibular branch of trigeminal nerve (CN V3)
Posterior 1/3 of the tongue: glossopharyngeal nerve (CN IX)
Posterior area of the tongue root: vagus nerve (CN X)
Gustatory innervation (taste buds) is as follows:
Anterior 2/3 of the tongue: chorda tympani branch of facial nerve (CN VII)
Posterior 1/3 of the tongue: glossopharyngeal nerve (CN IX)
Posterior area of the tongue root and taste buds of the larynx and upper esophagus: vagus nerve (CN X)
Lesion localization
Function
Brainstem Nucleus Innervation
Pathway Example
Most Cranial Nerves
Bilateral
Left Hemisphere →Right & Left Nuclei
Lower Face (CN VII)
Contralateral
Left Hemisphere →Right Lower Face Nucleus → Right Lower Face Muscles
Tongue (CN XII)
Contralateral
Left Hemisphere →Right Hypoglossal Nucleus → Right Tongue Muscles
Most cranial nerve nucleus receive bilateral upper motor neuron (supranuclear) innervation, except for:
CN VII (lower face): The motor nucleus for the lower face receives only contralateral cortical input. This is why a UMN lesion (e.g., stroke) causes contralateral paralysis of the lower face only, with sparing of the forehead (which is bilaterally innervated).
CN XI (partially): The spinal accessory nerve’s innervation of the trapezius muscle is predominantly contralateral. A UMN lesion can lead to contralateral trapezius weakness. Innervation to the sternocleidomastoid muscle is primarily ipsilateral.
CN XII (partially): The hypoglossal nerve’s innervation to the genioglossus muscle (responsible for tongue protrusion) is predominantly contralateral. A UMN lesion causes the tongue to deviate away from the side of the lesion upon protrusion.
Most cranial nerves do not decussate after their nucleus, except for:
CN IV (Trochlear Nerve): This is the major exception. The nerve fibers of CN IV decussate (cross) within the midbrain at the superior medullary velum before exiting the brainstem dorsally. This means the right trochlear nucleus controls the left superior oblique muscle, and vice versa.
