1) Explain how the VOR reflex can be used as a diagnostic tool to evaluate damage to the vestibular system. Make sure to explain how different levels (depths) of nervous system injury can be detected.

 1. When neural system injury occurs we can evaluate the depth of the damage using VOR. This reflex is based on the detection of head movement to coordinate the movement of the eyes so they can stay fixed on the object. The principle is that when heads move left eyes move right. The nerves that detect this horizontal movement of the head start in the horizontal semicircular canal in the inner ear, goes through the brainstem to the muscle that regulates eye movements.
The injured patient is placed on his back with the head position on 30degrees above horizontal. It is important to induce this reflex with the caloric because willing movement abolished this reflex. This is called caloric testing. Irrigating one ear with the cold water, it cools down the nerve and mimics head movement away from the irrigated ear. In normal subjects, there will be slow eye movement to the irrigated ear and then fast movement away called saccadic movement. If the patient saccadic movement is missing, we can conclude that the brainstem is intact but that the injury is in the cerebral hemispheres. Only the saccadic movement is regulated in within the cerebrum. If the only eye on the same side as irrigated ear shows only slow eye movement that means that injury occurred