The glossopharyngeal nerve is primarily responsible for which of the following?

The glossopharyngeal nerve, or cranial nerve IX, plays a crucial role in various functions, but it is primarily recognized for its contributions to taste and salivation. This nerve is responsible for providing taste sensations from the posterior one-third of the tongue, which is essential for the perception of flavor and influences the process of eating.

Additionally, it contributes to the stimulation of salivary glands, specifically the parotid gland, helping to facilitate digestion and the oral phase of swallowing. The nerve also has a sensory function involved in the detection of blood pressure and oxygen levels in the carotid body, which is important for cardiovascular regulation, but the core functions highlighted in the question relate directly to its role in taste and salivation.

In this context, the other options pertain to functions governed by different cranial nerves: hearing and balance are primarily associated with the vestibulocochlear nerve, facial expression is primarily controlled by the facial nerve, and speech and swallowing involve the vagus and hypoglossal nerves. Therefore, the selection of taste and salivation as the primary responsibility of the glossopharyngeal nerve is well-founded and aligns with its established functions.