Jaw Jerk
Overview
The jaw jerk is also known as the masseter inhibitory reflex; it involves the mandibular branch of the trigeminal nerve as both its afferent and efferent arms.
How to Elicit
- Place a finger horizontally over the chin with the mouth open, and then strike this finger with a tendon hammer.
Warn the patient beforehand!
While a slight jerk may be normal, an exaggerated jerk is a sign of an upper motor neuron lesion.
Interpretation
- Slight / absent jerkNormal, mandibular nerve (V3) lesion
- Exaggerated jerk (± clonus)Upper motor neuron lesion
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