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
Jaw Jerk Pathway
Receptors
Muscle spindle within mandible
Muscle spindle within mandible
Foramen
Foramen ovale
Foramen ovale
V3
Mandibular branch
Mandibular branch
Trigeminal Ganglion
Mesencephalic nucleus
Midbrain, pons
Midbrain, pons
Trigeminal Motor Nucleus
Upper pons
Upper pons
V3
Mandibular branch
Mandibular branch
Foramen
Foramen ovale
Foramen ovale
Muscle
Masseter
Masseter
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