Final answer:
The gag reflex and area postrema in the brain are activated when inducing vomiting by putting a finger down the throat, leading to a signal being sent to the medulla oblongata to start the emesis process.
Step-by-step explanation:
Using a finger down the throat to induce vomiting activates the gag reflex and involves the area postrema. The area postrema is part of the brain located adjacent to the fourth ventricle that can detect toxins in the bloodstream and stimulate emesis. This is possible because the area postrema is not fully protected by the blood-brain barrier. When the gag reflex is stimulated, it sends a message to the medulla oblongata, which activates the vomiting mechanism. Vagus nerve stimulation also plays a role, as it helps mediate the motor response needed for emesis.