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The gag reflex is a reflex contraction of the back of the throat, evoked by touching the soft palate, that prevents something from entering the throat except as part of normal swallowing. This helps prevent choking. It is also known as a pharyngeal reflex.
The afferent limb of the reflex is supplied by the glossopharyngeal nerve (cranial nerve IX), which inputs to the nucleus solitarius, and the efferent limb is supplied by the vagus nerve (cranial nerve X) from the nucleus ambiguus. Absence of the gag reflex is a symptom of a number of severe medical conditions, such as damage to the glossopharyngeal nerve, or the vagus nerve.