INCOORDINATION AND OTHER DISORDERS OF CEREBELLAR FUNCTION in Microsoft Office

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of the superior cerebellar peduncle, following their decussation, de- Thalamacortical fibers scend in the ventromedial tegmentum of the brainstem via the central Thalamus tegmental fasciculus and terminate Lateral Dentatorubral in the reticulotegmental and paraventral tract nucleus median reticular nuclei of the pons and inferior olivary nuclei of the Red medulla These nuclei, in turn, projDentotothalamic nucleus tract ect via the inferior cerebellar peduncle to the cerebellum, mainly the anterior lobe, thus completing a Superior cerebellar-reticular-cerebellar feedcerebellar peduncle back system (Fig 5-3) Globose Cerebellar Decussation The fastigial nucleus sends emboliform nuclei of brachium conjunctivum bers to the vestibular nuclei of both Descending sides and, to a lesser extent, to other division nuclei of the reticular formation of of peduncle the pons and medulla There are Dentate nucleus also direct ber connections with middle Cerebellar the alpha and gamma motor neupeduncles rons of the spinal cord The inferior inferior olivary nuclei project via the restiform body (inferior cerebellar peReticulotegmental nucleus duncle) to the contralateral cerebelFeedback Paramedian reticular nucleus lar cortex and corresponding parts (of medulla) of the deep cerebellar nuclei Thus thecerebellum in uences motor acFeedback tivity through its connections with the motor cortex and brainstem nuclei and their descending motor pathways The integration at the thalamic level of basal ganglionic in uences with those of the cereFigure 5-3 Dentatothalamic and dentatorubrothalamic projections via the superior cerebellar peduncle The bellum is detailed in Chap 4 Clinicopathologic observa- feedback circuit via the reticular nuclei and reticulocerebellar bers is also shown (Mollaret triangle) tions indicate that the cerebellar the dentate nucleus to the ventrolateral thalamus and motor cortex cortex, and the anterior lobe in particular, is organized somatotopThe dentatal neurons were shown to re just before the onset of ically This view has been amply con rmed experimentally by the volitional movements, and inactivation of the dentatal neurons demapping of evoked potentials from the cerebellar cortex, elicited layed the initiation of such movements The interpositus nucleus by a variety of sensory stimuli, and an analysis of the motor effects also receives cerebrocortical projections via the pontocerebellar produced by stimulation of speci c parts of the cerebellar cortex system; in addition, it receives spinocerebellar projections via the The topographic sensory representation of body parts based on intermediate zone of the cerebellar cortex The latter projections these experimental observations is assumed to be similar to the convey information from Golgi tendon organs, muscle spindles, motor map but is probably not as distinct The similarity between cutaneous afferents, and spinal cord interneurons involved in this scheme and the one derived from the study of human disease movement The interpositus nucleus res in relation to a movement becomes apparent when one considers the results of cerebellar leonce it has started Also, the prepositus nucleus appears to be resions discussed further on Diffuse degenerations of the cerebellum, sponsible for making volitional oscillations (alternating moveof course, have widespread effects, including motor, articulatory, ments) Its cells re in tandem with these actions, and their regugait and eye movements larity and amplitude are impaired when these cells are inactivated In addition, Thach has pointed out that the nucleus interpositus Role of the Deep Cerebellar Nuclei The physiologic studies of normally damps physiologic tremor; he has suggested that this may Allen and Tsukahara and those of Thach and colleagues have play a part in the genesis of so-called intention tremor described greatly increased our knowledge of the role of the deep cerebellar further on The fastigial nucleus controls antigravity and other musnuclei These investigators studied the effects of cooling the deep cle synergies in standing and walking; ablation of this nucleus nuclei during a projected movement in the awake macaque mongreatly impairs these motor activities key Their observations, coupled with established anatomic data, permit the following conclusions The dentate nucleus receives inNeuronal Organization of the Cerebellar Cortex Coordinated formation from the premotor and supplementary motor cortices via and uid movements result from a neuronal organization in the the pontocerebellar system and helps to initiate volitional movecerebellum, which permits a computational comparison between ments The latter are accomplished via efferent projections from