Jaw Jerk

Fifth Cranial Nerve: Masseter Muscles

As shown in Figure 13-1, put your left index linger horizontally on the patient's chin. Strike your finger when the patient has her mouth open about 2 cm. Bring the hammer from above downward in the direction of the arrow.

An abnormal response is prompt closure of the jaw. Most people have no response. Therefore, the reflex has no value in the diagnosis of segmental lesions.

A unilateral suprasegmental lesion does not produce an abnormal jaw jerk; a bilateral lesion does.

Figure 13-1. Jaw jerk is elicited by striking your own finger on the patient's chin while the patient's mouth is slightly open. The hammer motion is from above downward (arrow).

Figure 13-1. Jaw jerk is elicited by striking your own finger on the patient's chin while the patient's mouth is slightly open. The hammer motion is from above downward (arrow).

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