Jaw jerk reflex
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The jaw jerk reflex is a motor reflex used to test the status of a patient's trigeminal nerve (CN V). The mandible—-or lower jaw—-is tapped at a downward angle just below the lips at the chin while the mouth is held slightly open. Normally this reflex is absent or very slight. However in individuals with upper motor neuron lesions the jaw jerk reflex can be quite pronounced.
As with most other reflexes, the response to the stimulus is monosynaptic, with sensory neurons of the trigeminal mesencephalic nucleus sending axons to the trigeminal motor nucleus, which in turn innervates the masseter. This reflex is used to judge the integrity of the upper motor neurons projecting to the trigeminal motor nucleus. Both the sensory and motor aspects of this reflex are subserved by CN V.
It is not part of a standard neurological examination, being used rather if there are other signs of damage to the trigeminal nerve.
References
- Nolte, J. The Human Brain, 5th ed. Mosby: Missouri; 2002, p.307. ISBN 0-323-01320-1
- Blumenfeld, H. Neuroanatomy Through Clinical Cases. Sinauer Associates: Massachusetts; 2002, p. 484. ISBN 0-87893-060-4
Nervous system physiology: neurophysiology - reflex | |
|---|---|
| Cranial nerve | midbrain: Pupillary light reflex - Accommodation reflex pons/medulla: Jaw jerk reflex - Corneal reflex - Caloric reflex test/Vestibulo-ocular reflex - Gag reflex |
| Tendon reflexes | upper limb: Biceps reflex - Brachioradialis reflex - Extensor digitorum reflex - Triceps reflex lower limb: Patellar reflex - Ankle jerk reflex - Plantar reflex |
| Primitive reflexes | Galant - Grasp - Moro - Rooting - Stepping - Sucking - Tonic neck |
| Other | Baroreflex - Acoustic reflex - H-reflex - Oculocardiac reflex - Stretch reflex - Startle reaction - Optokinetic - Withdrawal reflex - Crossed extensor reflex |
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
