Jaw jerk reflex

Jaw Jerk Reflex
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The jaw jerk reflex is a type of stretch reflex used to test the status of a patient's trigeminal nerve (cranial nerve V) and the upper motor neuron pathways. It is a quick, involuntary response of the masseter muscle when the jaw is tapped.

Physiology

The jaw jerk reflex is a monosynaptic reflex that involves the afferent and efferent fibers of the trigeminal nerve. When the jaw is tapped, the muscle spindles in the masseter muscle are stretched, sending a signal through the mandibular branch of the trigeminal nerve to the trigeminal motor nucleus in the pons. The response is then sent back to the masseter muscle, causing it to contract.

Clinical Significance

The jaw jerk reflex is used in neurological examinations to assess the integrity of the trigeminal nerve and the central nervous system. A normal response is a slight closure of the jaw. An exaggerated jaw jerk reflex may indicate an upper motor neuron lesion above the level of the trigeminal nerve, such as in amyotrophic lateral sclerosis or multiple sclerosis.

Testing Procedure

To test the jaw jerk reflex, the patient is asked to relax their jaw, allowing it to hang slightly open. The examiner places their finger on the patient's chin and taps it with a reflex hammer. The normal response is a slight closure of the jaw.

Related Reflexes

• Knee jerk reflex
• Biceps reflex
• Triceps reflex

See Also

• Reflex arc
• Neurological examination
• Cranial nerves

External Links

• Trigeminal nerve on WikiMD
• Reflexes on WikiMD