Jaw Jerk

 
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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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