Cerebellum

CEREBELLUM Site: Dorsal to brain Connected to brain through brain stem by three peduncles I. Superior cerebral peduncle to midbrain II. Medial cerebral peduncle to pons III. Inferior cerebral peduncle to medulla Division z 2 large lateral cerebellar hemispheres z 1 central vermis Phylogenetic division I. Archicerbellum II. Paleocerebellum III. Neocerebellum Functional division Flocculonodular lobe Related to vestibular apparatus Control of body posture and equilibrium Anterior lobe and part of posterior lobe (spinocerebellum) Controls axial and limb movements and postural reflexes Remnant part of posterior lobe, cerebral cortex (neocerebellum) Skilled voluntary movements

CEREBELLAR CORTEX z z

Anterior grey matter of cerebellum is called cerebellar cortex Within white matter -4 pairs of nuclei – deep cerebellar nuclei

Cerebellar cortex is composed of 3 layers I. Outer molecular layer- endings of unmyelinated nerve fibres and nerve cells (stellate and basket cells) II. Middle purkinje cell layer – contains purkinje cell (biggest neuron) III. Inner granular layer- contains granule and golgi cells Input Afferent fibres z

Climbing fibres- arise from cells in inferior olivary nuclei Has one to one cell connection with purkinje cell and leads to their excitation.

z

Mossy fibres – axons of spinocerebellar , vestibulocerebellar, reticulo cerebellar, corticoponto cerebellar tract One mossy fibre connects with many granule cells

Output z Granule cells are always excitatory z Output of purkinje , golgi and basket cells are always inhibitory

Purkinje cell output is inhibitory to deep cerebellar nuclei, that receives excitatory stimuli from afferent fibres. Entire cerebellar circuit is concerned with modulatory. The excitatory output of deep cerebellar nuclei to brainstem and thalamus. Helps in coordinating the muscular movement (stellate ,basket, golgi cells) NOTE- transmitter secreted by stellate, basket, golgi and purkinje cells – GABA whereas granules cells secrete –Glutamic acid

FUNCTIONS z Controls the body posture and equilibrium z Control muscle tone and stretch reflexes. z Coordination of body movements both voluntary and involuntary , by appropriate regulation of time, rate, range, force and direction of muscle activity. LESIONS 1. Lesion of the cerebellar hemisphere-- produces dysfunction of same side of the body z

Atonia / hypotonia - -muscle tone reduced/lost

z

Nystagmus

z

Pendulous / weak deep reflexes

Asthenia, feebleness of movements, coarse intention tremors drunken gait. z

z z

Slow lalling speech Dysmetria.

Multiple Choice Questions: 1. Cerebellum is concerned with a) Control of body posture and equilibrium b) Control of muscle tone c) Control of stretch reflexes d) All

2. Lesion of cerebellum hemisphere results in a) Atonia b) Nystagmus c) Asthenia d) Dysmetria e) All of the above

3. Flocculonodular node of cerebellum is concerned with a) Body posture b) Hearing' c) Vision d) Fine movements

4. Tremor associated with lesion of cerebellum are a) Fine tremors b) Coarse intention tremors c) Present at rest d) All of the above

5. Dysmetria is seen in lesions of

a) b) c) d)

Cerebellum Cerebrum Thalamus Pyramidal tract