Expansion
Nine tastes it, ten gags it
Mnemonic
“9 in, 10 out”:
- Afferent - glossopharyngeal (IX), from the posterior pharyngeal wall
- Efferent - vagus (X), to the pharyngeal muscles
The same pairing governs swallowing and palatal elevation, which is why a lesion of either nerve abolishes the reflex.
Other cranial reflexes follow the same in and out logic:
- Corneal: in V1, out VII
- Pupillary light: in II, out III
- Jaw jerk: in V3, out V3, the only monosynaptic cranial stretch reflex
- Oculocardiac: in V1, out X
The gag reflex is absent in up to a fifth of normal people and is uncomfortable, so it is a poor test of swallow safety and should not be used as one.
Expansion
- Afferent - CN IX, glossopharyngeal nerve
- Efferent - CN X, vagus nerve