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Cerebellum
- 1. CEREBELLUM By- Prakhar Jain RIMS Raipur
- 2. Previous year questions Discuss the afferent connections of cerebellum. Discuss the functions of cerebellum in short. (2006, 2007) Describe regulation of posture in short. (2007) Write the functions of cerebellum. (2015) Difference between sensory ataxia and cerebellar ataxia. (2015, 2016) Draw a labelled diagram to show functional divisions of cerebellum and give the physiological significance of neuronal circuit within the cerebellar cortex.
- 3. Anatomical Divisions (1) The anterior lobe, (2) The posterior lobe, and (3) The flocculonodular lobe
- 5. Phylogenetical Divisions 1. Archicerebellum- First to develop during evolution. Consists of floccules and nodule. 2. Paleocerebellum- Evolved after archicerebellum. Consists of the entire anterior lobe and pyramis, uvula and parafloccules. 3. Neocerebellum- Last to evolve. Greatest development in humans. Consists of declive, tuber, ansiform and paramedian lobules.
- 6. Functional Divisions 1. Flocculonodular lobe 2. Vermis 3. Intermediate zone 4. Lateral zone
- 7. Flocculonodular lobe It is connected with the vestibular apparatus, therefore also called vestibulocerebellum. Concerned with control of body postures, maitaining equilibrium and vestibulo-ocular reflex.
- 8. Spinocerebellum So called because they receive information from spinal cord. Consists of the vermis and intermediate zones. Constitutes the entire anatomical anterior lobe and simplex lobe, pyramis, uvula and parafloccules. It is concerned with control of axial and limb muscles and postural reflexes.
- 10. Lateral zone It constitutes of more lateral regions of cerebellum such as lateral ansiform and paramedian lobules. It receives signals mainly from cerebral cortex. It is believed that this connectivity with the cerebral cortex allows the lateral zone to play important roles in planning and coordinating the body’s rapid sequential muscular activities.
- 11. Structure of Cerebellum In cross section, cerebellum have an outer grey matter and an inner white matter. The human cerebellar cortex is a large folded sheet, about 17 centimeters wide by 120 centimeters long, with the folds lying crosswise, and each fold is called a folium. Lying deep beneath the folded mass of cerebellar cortex are deep cerebellar nuclei.
- 12. Cortex The cerebellar cortex is composed of three layers- (1) Outer molecular layer (2) Middle purkinje layer (3) Inner granule layer
- 13. Molecular Layer Two types of nerve cells are present in molecular layer- 1. Stellate cells- star shaped 2. Basket cells- their axons forms a basket around the cell body of each purkinje cell they innervate.
- 15. Purkinje Cell Layer One cell thick layer. Flask shaped cells Biggest neuron in body Their axons are the only output of the cerebellar cortex which synapses with deep cerebellar nuclei.
- 17. Granule Cell Layer This layer have two types of cells- 1. Granule cells 2. Golgi cells
- 19. Neural Circuits of the Cerebellum
- 20. Afferent Pathways From Other Parts of the Brain
- 21. Corticopontocerebellar Tract- • Corticopontine fibres originates in the cerebral motor and premotor cortices (areas 3 and 4)and ends in pontine nuclei. • From the pontine nucleus, the pontocerebellar fibres cross to enter the cerebellum on the opposite side, through the middle cerebellar peduncle. • After entering, these fibres are distributed to all parts of cerebellum except flocculonodular lobe.
- 22. Olivocerebellar tract • It arises from the inferior olive and enters the cerebellum through contralateral inferior cerebellar peduncle • It is excited in the olive by fibers from the contralateral cerebral motor cortex, basal ganglia, brainstem nuclei, and spinal cord. • These supply all parts of cerebellar cortex through climbing fibres
- 23. Vestibulocerebellar Tract • It arises in the vestibular nuclei and the vestibular apparatus itself and enters the cerebellum through ipsilateral inferior cerebellar peduncle . • Almost all the fibres then gets terminated in the flocculonodular lobe.
- 24. Reticulocerebellar Tract • It originates in the lateral reticular nucleus. • It is distributed to whole cerebellar cortex through ipsilateral inferior cerebellar peduncle.
- 26. Dorsal Spinocerebellar Tract • The dorsal tract enters the cerebellum through the inferior cerebellar peduncle and terminates in the vermis and intermediate zones of the cerebellum on the same side as its origin. • It carries mainly kinaesthetic and cutaneous afferents from the trunk and leg.
- 27. Ventral Spinocerebellar Tract • The ventral tract enters the cerebellum through the superior cerebellar peduncle, and terminates in mainly vermis and anterior lobe on ipsilateral side. • These are excited mainly by motor signals arriving in the anterior horns of the spinal cord and carries large proportion of cutaneous and proprioceptive fibres from all parts of the body.
- 28. Deep Cerebellar Nuclei and the Efferent Pathways
- 29. Each time an input signal arrives in the cerebellum, it divides and goes in two directions: (1) directly to one of the cerebellar deep nuclei and (2) to a corresponding area of the cerebellar cortex overlying the deep nucleus. Then, a fraction of a second later, the cerebellar cortex relays an inhibitory output signal to the deep nucleus.
- 30. Reference- GUYTON AND HALL AK JAIN THANK YOU
Notes de l'éditeur
- So we will try to discuss all these questions today
- Upar wala- primary fissure Niche wala- postero lateral fissure
- Ant. Lobe – lingual, central lobule, culmen
- Axial portions of the body lie in the vermis part, whereas the limbs and facial regions lie in the intermediate zones. Postural reflexes keep the body upright and aligned. These reflexes are triggered by the effects of gravity on the body.
- This is a topographical representation of body in the sensory areas of vermis and intermediate zone. This representation is ipsilateral and inverted in the anterior lobe………. and bilateral and erect in the posterior lobe.
- It is concerned with skilled voulantry movements.
- Cross section- opposite to what is seen in spinal cord. Follia are marked from one another by fissures. These folia overlies the white matter which consists of afferent and efferent fibres.
- Molecular layer- various nerve endings also present in the m layer such as- dendrites of purkinje cells, axons of granule cells, and climbing fibres (inf. Olivary nucleus)
- Purkinje cells have extensive dendritic network that extends vertically into the outer molecular layer.
- Granule cell- These make exitatory synaptic contact with dendrites of many purkinje cells, golgi cells, basket cell and stellate cell. Golgi cell- . Their axons branch extensively and form inhibitory synaptic connections with the dendrites of granule cells.
- Granule cells- Each cell axon ascends to the outer molecular layer and then bifurcates to form a ‘T’. The two branches of the T run along the long axis of folium and are called parallel fibres. Golgi cells- Their dendrites projects outwards into the molecular layer and receives input from the parallel fibres. Their cell bodies receives input via climbing fibres and purkinje cells
- Classified into
- To be precise, they mainly goes to lateral divisions of cerebellar hemisphere.
- These climbing fibres establishes one to one connection with the purkinje cell dendrites and exite it to discharge. Its collaterals also excite the golgi cells as I have mentioned earlier.
- *also in uvula.
- Distributed mainly in vermis.
- The spinocerebellar pathways can transmit impulses at velocities up to 120 m/sec, which is the most rapid conduction in any pathway in the central nervous system. This speed is important for instantaneous apprisal of the cerebellum of changes in peripheral muscle actions.
- Located deep in the cerebellar mass on each side are three deep cerebellar nuclei—the dentate, interposed (globose and emboliform), and fastigial.
- Thus, all input signals that enter the cerebellum, eventually end in the deep nuclei in the form of initial excitatory signals followed a fraction of a second later by inhibitory signals. From the deep nuclei, output signals leave the cerebellum and are distributed to other parts of the brain.