Final answer:
The gag reflex test is used in neurological examinations to evaluate the sensory and motor functions of the glossopharyngeal (CN IX) and vagus (CN X) nerves, though it's not highly specific as it does not isolate the function of a single nerve.
Step-by-step explanation:
The testing of the gag reflex is an important part of a neurological examination as it involves both sensory and motor functions. The dorsal portion of the glossopharyngeal nerve (CN IX) provides general sensation from the pharyngeal walls, which includes afferent input for the gag reflex. When these areas are stimulated by a tongue depressor, a gag reflex should be elicited. Simultaneously, the vagus nerve (CN X) provides the efferent motor control necessary for contraction of the pharyngeal muscles, which is pivotal to the motor aspect of the complex gag reflex. The test, while aiding in the assessment of these cranial nerves, can be considered somewhat unspecific because both the glossopharyngeal and vagus nerves contribute to this reflex, so it does not isolate the function of a single nerve. To further evaluate the vagus nerve's function, one can test motor functions by having patients articulate consonant sounds such as "lah-kah-pah", observing the movement of the soft palate and arches, which should contract efficiently and symmetrically if the nerve is functioning properly.