C H A P T E R 32 Cerebellum The cerebellum is a softball sized structure located at the base of the skull Grab the back of your head just above where it meets your neck your hand is now cupped around your cerebellum As with most brain systems much of what we know about the cerebellum stems from symptoms of damage or pathology and from its connectivity with the rest of the brain From such evidence it has long been clear that the cerebellum is an important component of the motor system Severe abnormalities of movement are produced by pathologies of the cerebellum Cerebellar outputs influence systems that are unambiguously motor such as the rubro spinal tract and inputs to the cerebellum convey information known to be essential for movement such as joint angles and loads on muscles More recently it has become equally clear that the role of the cerebellum is not limited to movement This is indicated by its interconnections with nonmotor structures by the more subtle nonmotor deficits seen with cerebellar lesions and by functional imaging studies where regions of the cerebellum show activation during nonmotor tasks In moving toward a stronger understanding of the cerebellum one obvious task will be to identify the common aspects or computational demands that these motor and nonmotor functions share Research on the anatomy physiology and function of the cerebellum has been complemented and enhanced by computational approaches that emphasize the rules for input output transformation and how the cerebellar neurons and synapses implement this transformation This interdisciplinary approach was made possible by the seminal work of Eccles Ito and Szentagothai who in 1967 published The cerebellum as a neuronal machine which described most of the essential aspects of the cellular and synaptic orga Fundamental Neuroscience Third Edition nization of the cerebellum Soon after a remarkable paper was published in 1969 by David Marr who inferred some basic computational properties of the cerebellum solely on the basis of the wiring diagram that Eccles and associates had worked out Since then the numerous conceptual and practical advantages of working on the cerebellum have enabled a more detailed understanding of what the cerebellum computes and how its neurons and synapses produce this computation ANATOMY AND PHYLOGENETIC DEVELOPMENT OF THE CEREBELLUM The cerebellum is present in all vertebrates and in the most primitive prevertebrates myxinoids up through primates Jansen and Brodal 1954 Larsell 1967 1970 1972 In agnathans lampreys and hagfish it is a rudimentary structure that assists the functions of the well developed vestibulo ocular vestibulospinal and reticulospinal systems The cerebellum is somewhat larger in fishes where on the input side it processes sensory information from the vestibular lateral line and to a lesser extent proprioceptive and somatosensory systems On the output side it is connected to the vestibular and reticular nuclei Box 32 1 In amphibians the region of the cerebellum that receives proprioceptive and other sensory information is expanded This region called the corpus cerebella increases further in reptiles birds and mammals In these vertebrate classes it constitutes the largest portion of the cerebellum receiving proprioceptive somatosensory visual and auditory information and projecting to the tectum the red nucleus and the 751 2008 2003 1999 Elsevier Inc 752 32 CEREBELLUM BOX 32 1 THE GIGANTOCEREBELLUM The weakly electric fish family Mormyridae have an enormous cerebellar structure called the gigantocerebellum On a per body weight basis the gigantocerebellum is comparable in weight to the human cerebellum The largest portion of the gigantocerebellum called the valvula has a Purkinje cell layer that would stretch to cerebral cortex via the thalamus In primates the hugely expanded lateral hemispheres of the corpus cerebella are connected with the enlarged cerebral cortex Fig 32 1 The hemispheres receive information from the frontal parietal and visual cortices by way of pontine nuclei and project to the motor and premotor cortices as well as to more anterior portions of the frontal lobe Fig 32 2 Asanuma et al 1983a 1983b 1983c 1983d Middleton and Strick 1994 Orioli and Strick 1989 Sasaki et al 1976 Schell and Strick 1984 The Cerebellum Can Be Subdivided on the Basis of Phylogeny Anatomy and the Effect of Lesions Superficially the cerebellum consists of a threelayered cortex folded in thin parallel strips called folia leaves which in most species run roughly transverse to the long axis of the body Fig 32 2 The cerebellar cortex surrounds three pairs of deep cerebellar nuclei From medial to lateral the deep cerebellar nuclei are the fastigius the interpositus which is further divided into the globose and emboliform nuclei in humans and the dentate The deep cerebellar nuclei and the vestibular nuclei constitute the output structures of the cerebellum An inner mass of white matter contains axons that run between the cerebellar cortex and the deep cerebellar nuclei The cerebellum is divided into three lobes Jansen and Brodal 1954 The flocculonodular lobe vestibulocerebellum is located on the inferior surface and is separated from the posterior lobe via the posterolateral fissure Superior to the posterior lobe is the anterior lobe these two lobes are separated by the primary fissure The lobes are divided further into lobules Larsell 1967 1970 1972 Fig 32 2 which are numbered I X beginning at the dorsal anterior vermis and ending at the inferior posterior vermis Each lobule contains a number of folia Lobulation is fairly consis approximately 1 m if unfolded That length is similar to the length of the Purkinje cell layer in the entire human cerebellum The valvula receives inputs from the electrosensory organs the lateral line and possibly the visual system The functional significance of this massive expansion of the cerebellum is a mystery A 1 culmen 2 declive 3 vermal folium 4 vermal tuber 5 vermal pyramis 6 vermal uvula 7 quadrangular lobule 8 primary fissure 9 simplex lobule 10 superior posterior fissure 11 superior semilunar lobule 12 horizontal fissure 13 inferior semilunar lobule 14 ansoparamedian fissure 15 gracile lobule 16 prebiventral fissure 17 biventral lobule 18 secondary fissure 19 cerebellar tonsil B FIGURE 32 1 Cerebellar structure and functional subdivisions A Dorsal view of the human cerebellum B Functional subdivisions Adapted from Nieuwenhuys Voogd and
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