The gag reflex is an involuntary mechanism to prevent asphyxia. During general anaesthesia this reflex is paralysed which is why it is so important to get the airway in place. And to make sure someone hasn't eaten beforehand. Without the gag reflex they could inhale vomits into the lung.it is also known as the pharyngeal reflex which has its roots in the upper medulla.it connects with the glossopharyngeal nerve which is one of the 12 craniofacial nerves leading to the tongue.
