Jaw jerk reflex

Jaw Jerk Reflex

File:Jaw jerk reflex.jpg

Illustration of the Jaw Jerk Reflex

The Jaw Jerk Reflex or Mandibular Reflex is a neurological reflex that is used to test the integrity of the brainstem and trigeminal nerve. It is a monosynaptic reflex that provides information on the integrity of the motor pathways within the brainstem.

Mechanism

The Jaw Jerk Reflex is elicited by a brisk tap on the mandible (lower jaw) at the chin while the mouth is slightly open. This tap stretches the masseter muscle, which is innervated by the trigeminal nerve. The sensory limb of the reflex is the afferent limb of the trigeminal nerve, and the motor response is the efferent limb of the trigeminal nerve to the masseter muscle. The reflex is monosynaptic, meaning there is a direct connection between the sensory and motor neurons, without any interneurons.

Clinical Significance

The Jaw Jerk Reflex is typically absent or very slight in healthy individuals. However, a pronounced or exaggerated Jaw Jerk Reflex can be a sign of an upper motor neuron lesion, such as in stroke, multiple sclerosis, or amyotrophic lateral sclerosis (ALS). It can also be used to assess the level of consciousness in a patient, as the reflex is usually more pronounced in individuals who are relaxed or drowsy.

See Also

• Monosynaptic reflex
• Trigeminal nerve
• Upper motor neuron