An exaggerated jaw jerk is elicited in a patient. Which statement about this reflex is correct?

• A Both afferent and efferent limbs travel in the mandibular division of the trigeminal nerve, with the reflex centre in the midbrain
• B The afferent limb travels in the maxillary division and the efferent limb in the mandibular division, with the centre in the pons
• C The afferent limb travels in the facial nerve and the efferent limb in the trigeminal nerve, with the centre in the medulla
• D Both limbs travel in the mandibular division, with the reflex centre in the pons; exaggeration indicates an upper motor neuron lesion above the pons ✓

Explanation

Tapping the chin stretches the masseter spindle; proprioceptive fibres have cell bodies in the mesencephalic nucleus and project to the motor nucleus of the trigeminal nerve in the pons, whose axons close the jaw via the mandibular division. Both limbs therefore run in CN V and the centre is pontine. Because the reflex arc sits in the pons, an exaggerated response indicates a corticobulbar tract lesion above the pons, analogous to a brisk deep tendon reflex in corticospinal disease.

Reference: Gray's Anatomy for Students, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.