Cerebellum anatomy and clinical correlations

cerebellum anatomy and clinical correlations with the anatomy has been described

1. CEREBELLUM -ANATOMY AND CLINICAL ANATOMY

2. INTRODUCTION The cerebellum, containing half of the brain’s neurons, is primarily responsible for the coordination of movements , especially skilled voluntary ones, the control of posture and gait , and participation in the regulation of muscular tone . It may play a role in the modulation of the emotional state and in special aspects of cognition.

3. anatomy The cerebellum is located in the posterior fossa, beneath the tentorium cerebelli. Below and anteriorly, it is separated from the dorsal pons by the fourth ventricle and from the medulla and the dura mater covering the atlanto-occipital membrane by the cisterna magna.

4. Gross anatomy 2 laterally large hemisphere which are united by VERMIS. Cerebellar surface is divided by numerous curve transverse fissures giving it a laminated appearance. Primary fissure - deepest fissure in the vermis Anterior and posterior lobe

5. Grossly, there are three parts: (a) cerebellar hemispheres , two larger, lateral masses (b) vermis , a small, unpaired median portion that connects the hemispheres (c) flocculonodular (FN) lobe , a small, midline structure that lies on the anterior part of the inferior surface. The vermis is separated from the hemispheres by the paramedian sulci. The cerebellar tonsils are small, rounded lobules on the inferior aspect of the cerebellar hemispheres,

6. Cerebellar peduncles Superior Middle Inferior

7. Anatomical classification Anterior lobe Posterior lobe Flocculonodular lobe

8. Functional classification

9. Phylogenetical classification ARCHICEREBELLUM (FN LOBE) PALEOCEREBELLUM (anterior lobe) NEOCEREBELLUM( hemisphere)

10. Head - posterior vermis Neck and trunk - dorsal and ventral vermis Arms and legs - intermediate cortex

11. Cerebellar organisation Histology 3 layers and 5 cells The outermost molecular layer contains two types of inhibitory neurons, the stellate cells and the basket cells. They are interspersed among the dendrites of the Purkinje cells, the cell bodies of which lie in the underlying layer Purkinje layer The Purkinje cell axons constitute the main output of the cerebellar cortex, which is directed at the deep cerebellar and vestibular nuclei. Purkinje cells , entirely inhibitory and utilize the neurotransmitter GABA Granular cell layer Granular cell ( major input) - only excitatory Golgi cells

12. Axons of the granule cells travel long distances as parallel fibers, which are oriented along the long axis of the folia and form excitatory synapses with Purkinje cells. Four of the five cell types of the cerebellar cortex (Purkinje, stellate, basket, Golgi) are inhibitory; the granule cells are an exception and are excitatory. Afferent fibers to the cerebellum are of three types, (1) Mossy fibers , which are the main afferent input to the cerebellum, utilize aspartate; (2) Climbing fibers , which are the axons of cells in the inferior olivary nucleus and project to the Purkinje cells of the opposite cerebellar hemisphere. The neurotransmitter of the climbing fibers is probably glutamate, (3) Aminergic fibers , which project through the superior cerebellar peduncle and terminate on the Purkinje and granule cells in all parts of the cerebellar cortex.

13. The predominant afferent inputs to the cerebellum are via mossy fibers, which comprise the axons of the spinocerebellar tracts, and via the projections from pontine, vestibular, and reticular nuclei. They enter through all three cerebellar peduncles, but mainly the middle (pontine input) and inferior (vestibulocerebellar) ones.

14. Deep cerebellar nuclei The dentate nucleus receives information indirectly from the premotor and supplementary motor cortices via the pontocerebellar system and helps to initiate volitional movements. The dentatal neurons have been shown to fire just before the onset of volitional movements and inactivating these neurons delays the initiation of such movements The interpositus nucleus also receives projections from the cortex via the crossed pontocerebellar fibers; in addition, it receives spinocerebellar projections via the intermediate zone of the cerebellar cortex

15. The interpositus nucleus fires in relation to a movement once it has started. Also, the interpositus nucleus appears to be responsible for making volitional oscillations (alternating movements). the nucleus interpositus normally damps physiologic tremor and plays a part in the genesis of intention tremor. The fastigial nucleus r eceives projections from the spinocerebellar fibers and, like the interpositus, projects to the vestibular nuclei. It controls antigravity and other muscle synergies in standing and walking; ablation of this nucleus greatly impairs these motor activities.

16. Lateral cerebellum output Right lateral hemisphere Right dentate nucleus Superior cerebellar peduncle Cross at level of inferior colliculus Left red nucleus Left thalamus Premotor and motor cortex Left Corticospinal tract Pyramidal Decussation Right lateral CST DOUBLE DECCUSATION PRESENT

17. INTERMEDIATE CEREBELLUM OUTPUT VIA INTERPOSED NUCLEI SAME AS LATERAL ONE THROUGH LOWER PART OF RED NUCLEUS ( magno) - intermediate lobe also connects to the rubrospinal tract

18. Vermis output Vermis- fastigial nucleus Via superior cerebellar peduncle crosses to reach red nucleus - thalamus(vl)- cortex- uncrossed anterior corticospinal tract Via superior cerebellar peduncle gives connection to tectum - TECTOSPINAL TRACTS via inferior cerebellar peduncle - juxtarestiform body -vestibular nucleus( vestibulospinal tract) and reticular nucleus ( reticulospinal tract) Via superior cerebellar peduncle pass through opposite fastigial nucleus relays through opposite juxtarestiform bodies

19. Flocculonodular lobe output Vestibular nucleus - vestibulospinal tract MLF - vestibulo ocular eye movements

20. Cerebellar input CORTICOPONTOCEREBELLAR PATHWAY SPINOCEREBELLAR OLIVOCEREBELLAR

21. CORTICOPONTOCEREBELLAR PATHWAY Originates in the cerebral motor and promotor cortex and also in the somatosensory cortex. It passes by the way of pontine nuclei and Pontocerebellar tracts mainly to the lateral divisions of cerebellar hemisphere on opposite side of brain from the cerebral areas

22. Olivocerebellar tract originates from inferior olivary nucleus and crosses to reach the opposite cerebellum via the climbing fibres Vestibulocerebellar fibres, some of which originate in the vestibular apparatus and others from the brainstem vestibular nuclei almost all of them terminate in the fastigial nucleus of cerebellum Reticulocerebellar fibres, which originate in different portions of brainstem reticular formation and terminate in the mid line cerebellar areas( vermis)

23. Afferent pathways from periphery Dorsal spinocerebellar tract and the ventral spinocerebellar tract Dorsal tract enters the cerebellum via inferior cerebellar peduncle carrying position sense terminates in the Vermis and intermediate zones of cerebellum on the same sides of its origin. Ventral tract enter the cerebellum through the superior cerebellar Peduncle but it terminate on both sides of cerebellum

24. Blood supply of cerebellum cerebellum is supplied by the posterior inferior, anterior inferior and superior cerebellar arteries. The cerebellar arteries form superficial anastomoses on the cortical surface. The choroid plexus of the fourth ventricle is supplied by the posterior inferior cerebellar artery Sca upper part Aica fn and lateral part Pica inf part

25. Blood supply of cerebellum

26. Clinical manifestations

27. CEREBELLAR SIGNS Hypotonia with pendular jerk Tremors intention or kinetic both can be seen Ataxia and incoordination Dysmetria, dyssynergia and dysdiadokinesis as agonist antagonist agonist movement regulated by cerebellum is lost. Dysarthria scanning or staccato speech Loss of check, reflex rebound phenomena

28. Eye signs Pursuit - irregular or broken with saccadic intrusions Saccades - latency increased , velocity decreased Nystagmus- gaze evoked Rebound nystagmus Brun’s nystagmus- large amplitude and low frequency nystagmus on the side of lesion and low amplitude and high frequency on the opposite side in cases of cerebellopontine angle tumours. Ocular flutter or opsoclonus present - saccadic inclusion without a fixed intersaccadic interval

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