Final answer:
The vagus nerve is primarily responsible for the motor end of the gag reflex, as it activates the muscles required for gagging.
Step-by-step explanation:
The motor end of the gag reflex is primarily carried by the vagus nerve. This cranial nerve is responsible for initiating the contraction of muscles in the pharynx during the gag reflex. Testing of the glossopharyngeal nerve also plays a role in this reflex by relaying sensations from the pharyngeal walls which can trigger the reflex. However, when it comes to the motor response, the vagus nerve is the one that activates the necessary muscles to produce the gagging action.