Which cranial nerve is responsible for taste in the posterior one-third of the tongue?

The glossopharyngeal nerve, which is cranial nerve IX, is responsible for taste sensation in the posterior one-third of the tongue. This nerve innervates the taste buds located in this region and also contributes to sensation and autonomic functions in the area.

In addition to taste, the glossopharyngeal nerve has important roles in the movement of the stylopharyngeus muscle, which assists in swallowing, and it provides sensory information from the pharynx and the oropharynx. This blend of sensory activities alongside its taste function is crucial for the integration of taste perception and swallowing.

Understanding that the other cranial nerves listed serve different functions clarifies why the glossopharyngeal nerve is the correct choice. For instance, the hypoglossal nerve primarily controls motor functions of the tongue and does not have a role in taste sensation. The facial nerve is involved in taste, but specifically for the anterior two-thirds of the tongue. The trigeminal nerve has a primary sensory role, providing general sensation but not taste. Hence, the glossopharyngeal nerve is distinct in its specific function of taste in the posterior part of the tongue.