Introduction

Disorders of the cerebellum may have a large number of etiologies and, therefore, may be associated with a multitude of clinical signs. However, only a small number of clinical signs may be viewed as being specific for cerebellar dysfunction. These clinical hallmarks of cerebellar dysfunction include inaccurate, dysmetric limb movements, disordered gait, dysarthric speech, nystagmus, abnormal oculomotor control, as well as involuntary movements such as terminal and postural tremors. During recent years, a large number of studies have helped to clarify to a considerable extent both the role of the cerebellum in normal movement and the pathophysiological consequences of cerebellar dysfunction. This chapter reviews the major clinical signs of cerebellar disorders and attempts to interpret these signs in the framework of current concepts of normal and pathologic cerebellar motor physiology.

The neuroanatomy of the cerebellum is extensively reviewed in Chapter 2. This chapter briefly emphasizes two fundamental features of cerebellar neuroanatomy that seem to be critical for understanding its physiology. These two features are the organization of its input-output pathways and the consequent compartmentalization of cerebellar functions. The microarchitecture of the cerebellum is remarkably homogenous across different cerebellar subdivisions. In particular, the cerebellar cortical circuitry consisting of two input pathways, the mossy fiber/parallel fiber system and the climbing fiber system, and a single output pathway, the Purkinje cells that connect the cerebellar cortex with the deep nuclei, is remarkably homogeneous across different cerebellar subdivisions.