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The cerebellum, principally a motor organ, is responsible for the coordination of movements, especially skilled voluntary ones, the control of posture and gait, and the regulation of muscular tone. In the last decade it has come to be appreciated that the cerebellum may play a role in the modulation of the emotional state and some aspects of cognition. The mechanisms by which these functions are accomplished have been the subject of intense investigation by anatomists and physiologists. Their studies have yielded a mass of data, testimony to the complexity of the organization of the cerebellum and its afferent and efferent connections. A coherent picture of cerebellar function is now emerging, although it is not yet possible, with a few notable exceptions, to relate each of the symptoms of cerebellar disease to a derangement of a discrete anatomic or functional unit of the cerebellum.

Knowledge of cerebellar function has been derived mainly from the study of natural and experimental ablative lesions and to a lesser extent from stimulation of the cerebellum, which actually produces little in the way of movement or alterations of induced movement. Furthermore, none of the motor activities of the cerebellum reaches conscious kinesthetic perception; its main role, a critical one, is to assist in the initiation and modulation of willed movements that are generated in the cerebral hemispheres. The following discussion of cerebellar structure and function has, of necessity, been simplified; a fuller account can be found in the writings of Jansen and Brodal, of Gilman, and of Thach and colleagues.

The classic studies of the comparative anatomy and fiber connections of the cerebellum led to its subdivision into three parts (Fig. 5-1): (1) The flocculonodular lobe, located inferiorly, which is phylogenetically the oldest portion of the cerebellum and is much the same in all animals (hence archicerebellum). It is separated from the main mass of the cerebellum, or corpus cerebelli, by the posterolateral fissure. (2) The anterior lobe, or paleocerebellum, which is the portion of the corpus cerebelli rostral to the primary fissure. In lower animals, the anterior lobe constitutes most of the cerebellum, but in humans it is relatively small, consisting of the anterosuperior vermis and the contiguous paravermian cortex. (3) The posterior lobe, or neocerebellum, consisting of the middle divisions of the vermis and their large lateral extensions. The major portions of the human cerebellar hemispheres fall into this, the largest, subdivision.

Figure 5-1.

Diagram of the cerebellum, illustrating the major fissures, lobes, and lobules and the major phylogenetic divisions (left labels).

This anatomic subdivision corresponds roughly with the distribution of cerebellar function based on the arrangement of its afferent fiber connections. The flocculonodular lobe receives special proprioceptive impulses from the vestibular nuclei and is therefore also referred to as the vestibulocerebellum; it is concerned essentially ...

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