Cerebellum

Three anatomical portions of the cerebellum are:

Flocculonodular lobe and fastigial nuclei: archicerebellum.

Anterior lobe: palaeocerebellum: vermis and paravermis; globose and emboli-form nuclei.

Posterior lobe: neocerebellum: cerebellar hemispheres, dentate nuclei. Three functional subdivisions of the cerebellum are:

Flocculonodular lobe (vestibulocerebellum): involved in the maintenance of equilibrium and balance, and in smooth pursuit and saccadic eye movements.

Anterior lobe: involved in the maintenance of posture and muscle tone. Movement is monitored through input from proprioceptors via the posterior spinocerebellar and cuneocerebellar tracts.

Posterior lobe: involved in the learning, co-ordination and execution of skilled movement that is initiated at a cerebral cortical level (trajectory, velocity, acceleration). Co-ordination of movement is achieved by the integration of afferent somatic sensory information with motor output from the cerebrum and brain stem.

This sensory information can be tactile, auditory, vestibular, visual and visceral.

Broadly speaking the cerebellum comprises deep nuclei, which receive excitatory inputs from mossy fibres and climbing fibre collaterals and provide excitatory projections to nuclei in the brain stem and thalamus, and the cerebellar cortex, which receives excitatory inputs from mossy fibres and climbing fibre collaterals and provides inhibitory projections to the deep nuclei via the Purkinje cells.

There are five cell types: the Purkinje, stellate, basket, Golgi and granule cells. Three types of afferent fibres are identifiable:

Mossy

Climbing

Aminergic: y p

Dopaminergic t

Serotoninergic a

The sources of inputs to the cerebellum are from the spinal cord, the vestibular |

s nuclei, the motor cortex and the brain stem (red nucleus, reticular nuclei, inferior olivary nuclear complex).

The cerebellar inputs via the inferior cerebellar peduncle come from the ipsi-lateral spinal cord, inferior olive and the vestibular nuclei. The inputs via the middle cerebellar peduncle arise from contralateral pontine nuclei. The projection fibres in the superior cerebellar peduncle go to the ventro-lateral nucleus of the contralateral thalamus.

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