Question

Which nerve is required for GAG reflex

• A. 9th cranial nerve
• B. 10th cranial nerve
• C. 11th cranial nerve
• D. 12th cranial nerve

Answer 1

The Correct Option is A

The Gag Reflex (pharyngeal reflex) requires the $9^{th}$ cranial nerve (Glossopharyngeal nerve) as its afferent limb.

Reflex arc of the Gag Reflex:
- Stimulus: touching the posterior pharynx, soft palate, or tonsillar pillars
- Afferent: $CN\;IX$ (Glossopharyngeal) -- sensory from posterior pharynx to nucleus tractus solitarius and nucleus ambiguus
- Efferent: $CN\;X$ (Vagus) -- motor to pharyngeal constrictors, causing contraction

Clinical significance:
- An absent gag reflex may indicate a lesion of CN IX or CN X
- The gag reflex is used to assess brainstem integrity (especially in comatose patients)

Other cranial nerves -- roles:
- $CN\;X$ (Vagus): efferent limb of gag reflex
- $CN\;XI$ (Accessory): trapezius, sternocleidomastoid
- $CN\;XII$ (Hypoglossal): tongue movements

\[\boxed{\text{9th cranial nerve (Glossopharyngeal)}}\]