Which cranial nerve is involved in the sensation of taste and the gag reflex?

The glossopharyngeal nerve, known as cranial nerve IX, plays a crucial role in both the sensation of taste and the gag reflex. It is responsible for carrying taste sensations from the posterior one-third of the tongue, providing the perception of taste for this area. Additionally, the glossopharyngeal nerve contributes to the gag reflex by innervating the pharynx, which is essential for triggering this protective reflex when the throat is stimulated.

In the context of cranial nerves involved in taste and reflexes, the other options do not perform these specific functions. The accessory nerve primarily functions in motor control of certain neck muscles, while the vagus nerve, although involved in many autonomic functions and some sensations, does not specifically mediate taste in the same way as the glossopharyngeal nerve. The hypoglossal nerve is primarily responsible for motor control of the tongue and does not have a role in taste sensation or the gag reflex. This makes the glossopharyngeal nerve the correct answer for this question regarding taste and the gag reflex.