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Signs
 
 

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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