A stretch reflex that manifests as the contraction of the masseter and the temporalis muscles in response to the tapping of the lower jaw, and is used in neurological testing to determine the status of the trigeminal nerve
A stretch reflex is a reflex reaction characterized by muscle contraction due to the stimulation of the muscle proprioceptors. When the muscle is stretched, the body reacts by resisting the stretch by reflex. Some of the stretch reflexes are jaw jerk reflex, biceps reflex, brachioradialis reflex, triceps reflex, patellar reflex, and ankle jerk reflex.
The jaw jerk reflex is a stretch reflex wherein the masseter and the temporalis muscles contract in response to the tapping of the lower jaw. This reflex is also used in neurological examinations to determine the status of the trigeminal nerve (cranial nerve V). The test is done by tapping at a downward angle the lower jaw through the chin just below the lips. The body responds by the masseter muscles jerking the lower jaw upwards. Under normal conditions, the individual would not demonstrate this reflex reaction. However, those with upper motor neuron lesions will have marked jaw jerk reflex reaction.
- masseter reflex