Neural circuit of cerebellum,

cerebellum signal transmission process, cerebellum, brain anatomy, neural function, neural physiology, neural circuit

1. NEURAL CIRCUIT OF CEREBELLUM By MEENALI MISHRA A13156216001 M.Sc. Medical Physiology (3 rd Semester)

2. CEREBELLUM Largest part of the hindbrain & lies behind the Pons & medulla oblongata. Situated in the dorsal aspect of the brainstem & is connected to it by three cerebral peduncle on either side: Superior peduncle( brachium conjunctivum ). Middle peduncle( brachium pontis ). Inferior peduncle( restiform body ).

3. SUBDIVISIONS OF THE CEREBELLUM Composed of central vermis & two cerebral hemispheres on either side. PHYLOGENIC DIVISIONS: Archicerebellum Flocculonodular lobe & lingula. Palleocerebellum Anterior lobe except- lingula. Posterior lobe- pyramis, uvula. Neocerebellum Whole posterior lobe except- pyramis & uvula.

4. FUNCTIONAL SUBDIVISIONS: Vestibulocerebellum: Consists of flocculonodular lobe & lingula. Vestibular connections. Control body posture & equilibrium. Spinocerebellum: Includes vermis except nodule & lingula. Helps in controlling the activities of distal limb muscles Cerebrocerebellum: Consists of lateral portions of cerebral hemispheres. Helps in planning & programming movements.

5. STRUCTURE OF CEREBELLUM Outer Cerebellar Cortex Molecular layer. Purkinje cell layer. Granule cell layer. Inner core of White Matter Projection fibres. Association fibres. Commissural fibres. Deep Cerebellar Nuclei Dentate nucleus. Emboliform nucleus. Globose nucleus. Fastigeal nucleus.

6. LAYERS OF THE CEREBELLAR CORTEX Outer Molecular Layer: Consists of Stellate cells & Basket cells Innumerable synapses present executing a large amount of integrative work. Intermediate layer of Purkinje Cells: Have large flask shaped bodies with freely branching dendrites extending into the molecular layer & one axon passing to the cerebellar nuclei. Contains cell bodies of Purkinje cells. Inner Granular Layer: Contains small Granule cells & Golgi cells. Have multiple short dendrites & one long axon. Axon ascends to the molecular layer & bifurcates into the transverse branches parallel to the surface.

7. NEURONES IN THE CEREBELLAR CORTEX: Purkinje cells Granule cells Stellate cells Basket cells Golgi cells

8. PURKINJE CELLS: Biggest neurons in the body. Have extensive dendritic arbors that extend throughout the molecular layer. Cells receive the climbing fibres at the stem of dendritic tree. Also receives axons of Stellate cell & basket cells. Axons of these cells project to the deep cerebellar nuclei & few to the vestibular nuclei. GRANULE CELLS: Small, numerous, spherical neurons occupying greater part of the granular layer. Axons go up the molecular layer & bifurcate like letter ‘T’ called the parallel fibre. These fibres connect the Stellate cells, basket cells & Golgi cells. Mossy fibres makes glomerular synapse with the dendrites of the granule cells

9. STELLATE CELLS: Confined to the molecular layer. Dendrites synapse with the parallel fibres while the axons synapse with the dendrites of Purkinje cell(near their origin). BASKET CELLS: Lie in the deeper part of the molecular layer. Axons form networks around the cell bodies of Purkinje cells. GOLGI CELLS: Large stellate cells lying in the granular layer. Dendrites which project into molecular layer receive inputs from the parallel fibres. Golgi cells are responsible for feedback inhibition of granule cells. The stellate cells, basket cells & Golgi cells act as interneurones & are inhibitory

10. CONNECTION OF CEREBELLUM Incoming Fibres CLIMBING FIBRES: Bring excitatory inputs. Bring proprioceptive inputs along with other information. Give collaterals to deep cerebellar nuclei & end like creepers on primary dendrites of Purkinje cells. MOSSY FIBRES: Carry proprioceptive inputs from all parts of body plus cerebral cortex via the pontine nuclei to the cerebellar cortex. Give collaterals to the deep cerebellar nuclei & end on the dendrites of the granule cells. One mossy fibre communicates with many granule cells

11. Climbing Fibres: inferior olivary nucleus Cerebellum(Purkinje cells) Mossy Fibres: pontine nuclei Cerebellum( Glomerulus ) Climbing Fibres Mossy Fibres Olivocerebellar Tract Spinocerebellar Tract Vestibulocerebellar Tract Reticulocerebellar Tract Cuneocerebellar Tract Corticocerebellar tract

12. Outgoing Fibres Outgoing fibres from cerebellum are axons of the deep cerebellar nuclei together with some P cell axons. Cells of nuclei get excitatory collaterals from climbing & mossy fibres but inhibitory influence from axons of the purkinje cells. Excitatory output of cerebellum goes to the thalamus, red nucleus, reticular formation, olivary complex, vestibular nuclei etc. Cerebellar projection is sent to motor cortex, brain stem & spinal cord to achieve control of movements.

13. The Circuit Within The Cerebellum Climbing fibres, mossy fibres & granule cells are stimulatory whereas Purkinje cells, basket cells, Stellate cells & Golgi cells are inhibitory. One climbing synapse with one P cell & stimulates it whereas one Mossy fibre makes contact with many granule cell which in turn make contact with many P cell through the parallel fibres & stimulates these cells. One mossy fibres stimulates many Purkinje cells through the granule cells. Parallel fibres makes contact with the basket cell, stellate cells & Golgi cells. Mossy fibres contact with the Golgi cells along with the granule cells.

14. Stellate & basket cells end on the purkinje cells & Golgi cells end on the granule cells. Climbing & mossy fibres send collaterals to the deep cerebellar nuclei. Output of the cerebellar nuclei form output of the cerebellum. Golgi cells are stimulated by mossy & parallel fibres & they inhibit granule cells. Basket cells & stellate cells are excited by parallel fibres & they inhibit the granule cells.

15. Processing of information in cerebellum occurs as follows: Impulses entering the cerebellum take courses, one through deep cerebellar nuclei & other through the circuitry in the cortex. Result of cortical integration is ultimately presented in deep cerebellar nuclei. Final output of the nuclei is the output of the cerebellum & is distributed to different parts of CNS

16. CONNECTION OF CEREBELLUM The afferent (entering) & efferent(leaving) connecting the cerebellum with the extra cerebellar regions run through the three large bundles known as superior, middle & inferior cerebellar peduncles. INFERIOR CEREBELLAR PEDUNCLE (Restiform Body) AFFRENTS: Dorsal Spinocerebellar tract. External Arcuate fibres. Vestibulocerebellar tract. Olivocerebellar tract. Tectocerebellar tract. EFFERENTS: Fastigiovestibular tract & Fastigiobulbar tract. Cerebello-olivary tract.

17. MIDDLE CEREBELLAR PEDUNCLE (Brachium Pontis) AFFERENTS: Pontocerebellar tract. Fibres from cerebellum to cerebellum. SUPERIOR CEREBELLAR PEDUNCLE (Brachium Conjunctivum) AFFERENTS: Ventral spinocerebellar tract. Tectocerebellar tract EFFERENTS: Dentatothalamocortical tract. Dentatorubrothalamic tract.

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