Which cranial nerve provides taste sensation to the posterior 1/3 of the tongue?

The glossopharyngeal nerve, which is cranial nerve IX, is responsible for providing taste sensation to the posterior one-third of the tongue. This nerve also plays a role in the gag reflex and contributes to the sensation of touch and pain in that area. The taste fibers of the glossopharyngeal nerve are specifically activated by the presence of taste stimuli, allowing the perception of flavors in the posterior region of the tongue.

In contrast, other cranial nerves serve different functions related to the tongue. For instance, the facial nerve, or cranial nerve VII, primarily innervates the anterior two-thirds of the tongue for taste sensation. The trigeminal nerve, cranial nerve V, is mainly responsible for the sensory innervation of the tongue, covering aspects like general touch and pain but not taste. The vagus nerve, cranial nerve X, has responsibilities that extend beyond the tongue, including functions in the throat and thoracic organs, but it does not provide significant taste sensation to the tongue. Understanding the specific roles of these cranial nerves clarifies why the glossopharyngeal nerve is the correct answer for taste in that particular region of the tongue.