The gag reflex is a contraction of the pharyngeal muscles and elevation of the soft palate when the back of the throat is touched. The sensory side is carried by the glossopharyngeal nerve and the motor side by the vagus nerve. Its centre is in the medulla.
| Nerve root | CN IX (afferent), CN X (efferent) |
|---|---|
| Area | Posterior pharyngeal wall or back of the tongue |
| How to test | The examiner touches each side of the back of the throat with a tongue depressor or swab and watches for gagging and symmetric elevation of the soft palate. |
| Muscles | |
| Nerve Supply | Glossopharyngeal nerve (CN IX); Vagus nerve (CN X) |
Helps protect the airway by expelling objects that touch the back of the throat.
The gag reflex is absent in a sizeable minority of healthy people, so its absence alone does not prove a problem and does not reliably predict safe swallowing. One-sided loss, or the uvula pulling away from one side when the palate lifts, is more meaningful and suggests a lesion of the glossopharyngeal or vagus nerves or the medulla. Absence is part of the brainstem tests for brain death.
A stroke in the territory of the vertebral or posterior inferior cerebellar artery damages the nucleus ambiguus, causing a weak gag, swallowing difficulty and hoarseness.
Lower motor neuron weakness of the muscles supplied by CN IX, X and XII, as in motor neuron disease, causing a reduced gag and difficulty swallowing and speaking.
Absence of the gag and cough reflexes is part of the clinical criteria for brain death.
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