66. Overshoot

What is Being Tested?

Normal performance of these motor tasks depends on the integrated functioning of multiple sensory and motor subsystems. These include position sense pathways, visual pathways, lower motor neurons, upper motor neurons, the basal ganglia, and the cerebellum. Thus, in order to convincingly demonstrate that abnormalities are due to a cerebellar lesion, one must first test for normal joint position sense, vision, strength, and reflexes and confirm the absence of involuntary movements caused by basal ganglia lesions. As already mentioned, appendicular ataxia is usually caused by lesions of the cerebellar hemispheres and associated pathways, while truncal ataxia (see the following two sections, on the Romberg test and on gait) is often caused by damage to the midline cerebellar vermis and associated pathways (see Figures 15.3 and 15.9 in Neuroanatomy through Clinical Cases 3e).