The jaw reflex, also known as the jaw-jerk reflex, is elicited by tapping the chin or a device placed between the teeth, causing the jaw to jerk. Here's how it's done:
- Positioning: The person being tested should be relaxed and have their mouth slightly open.
- Application: A small piece of board or similar object is placed between the upper and lower teeth, or the examiner may tap the chin directly.
- Stimulus: A light tap is delivered to the board or the chin using a reflex hammer.
- Response: A normal response is a slight or absent closure of the jaw. An exaggerated closure suggests an upper motor neuron lesion.
Essentially, the transient stretching of the jaw-closing muscles produced by the tap results in the contraction of those same muscles. According to the provided reference, "a jerk of the jaw is initiated by lightly tapping a small piece of board placed between the upper and lower teeth or against the chin. The transient stretching of jaw-closing musculatures produces a contraction of the jaw-closing muscle. This is a stretch reflex similar to the knee-jerk reflex."
