Functional Anatomy Of The Intermediate Cerebellum In The Rat

textabstractThe cerebellum is situated in the posterior part of the scull, dorsal to the brainstem and pontine nuclei (Fig.1). Despite the fact that it is called “little brain” it harbors about half of the total number of neurons within the central nervous system (Kandel, 2003). The cerebellum is divided into an anterior lobe and a posterior lobe by the deep primary fissure. In addition, the posterior lobe is separated from the flocculonodular lobe by the posterolateral fissure. Transverse (interlobular) fissures divide the cerebellum further into 10 lobules (numbered I to X; Larsell, 1952; Larsell and Jansen, 1970). These lobules can be further sub divided by a various amount of foliation according to species (Figure 1). From medial to lateral, the cerebellum is divided into a vermis and a laterally positioned hemisphere. Amongst the two the paravermis or intermediate cerebellum is located, the organization and function of which will be the focus of this thesis. The cerebellum consists of a superficially located cortex, which, due to the impressive foliations reaches an enormous surface in the human. Deep in the white matter of the cerebellum the cerebellar nuclei are located which provide the output of the cerebellum. The cerebellum is connected to the brainstem by three cerebellar peduncles (superior, middle and inferior). Afferent connections (see 1.3) are found in all three peduncles and contact neurons located in the cerebellar cortex and/or the cerebellar nuclei (see 1.2 and 1.4). Efferent fibers leave the cerebellum via the superior cerebellar peduncle or via the uncinate tracts. The Purkinje cell layer of the flocculonodular lobe projects directly to the vestibular nuclei. Functionally, the cerebellum is divided into three regions; the phylogenetically oldest one presumably is the vestibulocerebellum, which more or less equals the flocculonodular lobe, and is involved in controlling balance and eye movements. The second part anatomically consists of the vermis and paravermis and is referred to as the spinocerebellum due to the fact that it receives abundant somatosensory input from the spinal cord. It is thought to be mostly involved in reflexive and/or unconsciously executed motor control of the striated muscles. Finally, the cerebrocerebellum, consisting of most of the hemispheres, is phylogenetically the youngest addition to the cerebellum and receives its input almost exclusively related to and from the cerebral cortex. It is concerned with the planning, coordination and learning of complex movements but has also been implicated in cognitive functions (Schmahmann, 1991; Gao et al., 1996). The cells that make up the cerebellum, their in- and output relations and their possible functions will be addressed.