Cerebellum

Yung-Yang LinInstitute of Brain Science

National Yang-Ming University

20090513

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Reference:

Outline • Anatomy• Cellular structure• Synaptic organization• Functional properties

• Balance and eye movement • Body and limb movement• Somatosensory information• Feed-forward mechanims• Planning movement• Cognitive function• Motor learning

• Pathology

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• Cerebellum – 10% of the total volume of the brain– More than half of all its neurons– Highly regular manner– Organized projection

• Receiving projection from brain and spinal cord• Projecting to different motor systems

– Motor system modulation• Evaluating disparities between intention and action• Adjusting the operation of motor centers

– Three aspects of the cerebellum’s organization1. Providing with extensive information2. Focusing on the premotor and motor system3. Modifying the synaptic transmission in the circuit modules

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Dorsal view

Ventral view

Midsagittal view

Deep nuclei

output

output

inputinput

Different views of cerebellum

• Composition of cerebellum– Outer gray matter (cerebellar cortex)– Inner white matter– 3 pairs of deep nuclei

• Fastigial nucleus• Interpose nucleus (globose nucleus, emboliform nucleus)• Dentate nucleus

• Cerebellar tracts– Inferior cerebellar peduncle (afferent projection)– Middle cerebellar peduncle (afferent projection)– Superior cerebellar peduncle (efferent projection)

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Anatomically distinct lobes

– Distinct lobes (horizontal)• Anterior lobe• Primary fissure• Posterior lobe• Posterolateral fissure• Flocculonodular lobe

– Distinct lobes (longitudinal)• Vermis• Intermediate part of hemisphere• Lateral part of hemisphere

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Projections of cerebellum

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Cellular structure of cerebellum

– 3 layers• Molecular layer• Purkinje cell layer• Granular layer

– 5 neuronal types• Inhibitory (GABA)

– Stellate neuron– Basket neuron– Purkinje neuron– Golgi neuron

• Excitatory (Glu)– Granule cell

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Synaptic glomerulus

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• Excitatory input of cerebellum

– Mossy fiber• Originate: nuclei in the spinal cord and brain stem • Carry : sensory information• Terminate on: dendrites of granule cells

– Climbing fiber• Originate: inferior olivary nucleus• Carry: somatosensory, visual, or cerebral cortical information• Terminate on: cell bodies and proximal dendrites of purkinje neurons

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• Output of granule cell– Parallel fibers

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• Excitatory inputs to Purkinje cells– Parallel fibers • 1 Purkinje cells receives million inputs

– Climbing fibers • 1 climbing fiber contacts 1-10 Purkinje cells• Arranged topographically

• Inhibitory inputs to Purkinje cells– Stellate interneurons– Basket interneurons– Golgi interneurons

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Synaptic organization of cerebellum

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The geometry of the principal connections 15

Mossy fiber

Granule cell

Parallel fiber

Purkinje cell(+)

Climbing fiber

(+)

• Complex spike– An initial large amplitude spike

followed by a high-frequency burst of smaller amplitude action potential

– Evoked by climbing fibers

• Simple spike– A brief excitatory postsynaptic

potential that generates a single action potential

– Evoked by parallel fibers

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Complex spikeSimple spike

Mossy and climbing fibers encode peripheral and descending information

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Mossy fiber Granule cell Parallel fiber Simple spike

Spontaneous activity(ex. Sensory stimuli)

Change in firing frequency

Encode the magnitude and duration of peripheral stimuli

Climbing fiber Complex spike

Change in firing frequency

Synchronization of complex spikes in the Purkinje neurons

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Climbing fibers modulate parallel fibers

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Mossy fiber Granule cell Parallel fiber Simple spike

Spontaneous activity(ex. Sensory stimuli)

Change in firing frequency

Encode the magnitude and duration of peripheral stimuli

Climbing fiber Complex spike

Change in firing frequency

Climbing fiber activity produces long-lasting effects on the synaptic efficacy of parallel fibers

• Climbing fiber action potentials reduce the strength of the parallel fiber input to the Purkinje neurons.

• Activity in climbing fibers can induce selective long-term depression (LTD) in the synaptic strength of parallel fibers.

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Functional properties of cerebellum

• Balance and eye movement • Body and limb movement• Somatosensory information• Feed-forward mechanims• Planning movement• Cognitive function• Motor learning

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• Balance and eye movement – Vestibulocerebellum

(flocculonodular lobe)• Receives input from :

semicircular canals and otolith organs• Senses motion of head and

position relative to gravity

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• Lesion– Impairing • Eye movement during head rotation• Movement of limbs and body during

standing and walking

– Difficulty maintaining balance– Pattern• Separating their feed widely• Moving legs irregularly

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Precerebellar neuclei

Sensory maps in cerebellum

–Vermis• Head and trunk

–Cerebellar hemisphere• Limb

–Fractured somatotropy• The same body part in

different locations

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Somatotopy in deep cerebellar nuclei

– Arranging to receive projection• Two maps

– Dorsal and ventral surfaces – Intermediate and lateral zone

– Projecting arrangement • Magnocellular red nucleus• Primary motor cortex via thalamus

– Intermediate zone (spinocerebellum)

– Lateral zone (cerebrocerebellum)

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The Spinocerebellum Modulates the Descending Motor Systems in the Brain Stem and Cerebral Cortex

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Vermis

Fastigal nucleus

Brain stem reticular formation

Lateral Vestibular nucleus

Spinal cord

Thalamus

Control motor cortex

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Lateral hemisphere

Dentate nucleus

Thalamus

Motor cortex

Control motor cortex

Intermediate hemisphere

interposed nuclei

The Spinocerebellum Uses Feed-Forward Mechanisms to Regulate Movements

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position

velocity

biceps

triceps

Vilis and Hore, 1977

• Lesion – Cerebellar hypotonia• Reducing the excitability of motor neurons and muscle tone

– Dysmetria (abnormal measure)• Disrupting the accuracy of reaching movement

– Ataxic (loss of order)• The path of hand in reaching is curved

– Terminal tremor • Hands oscillate irregularly around the target

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Cerebrocerebellum Is Involved in Planning Movement and Evaluating Sensory Information for Action

• Cerebrocerebellum (Lateral hemisphere)– Part of a high-level internal feedback circuit– Regulating cortical motor programs– Pathway

cortical input pontine nucluei middle cerebellar peduncle contralateral dentate nucleus lateral hemisphere

– Lesions • disrupting motor planning and prolonging

reaction time• Decomposition of movement

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Cognitive functions in cerebellum33

Cerebellum participates in motor learning34

Normal Patients

Distinctive symptoms and signs in cerebellar disease

• A lesion in the right cerebellar hemisphere– Delaying the initiation of movement

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• Dysmetria – Inaccuracy in range and direction

• Decomposition of movement

• Tremor increasing

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• Dysdiadochokinesia– Irregular pattern of alternating movements

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Thanks for attention

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39Anatomy The Cerebellum Has Three Functionally Distinct RegionsCellular structureCerebellar Circuits Consist of a Main Excitatory Loop and an Inhibitory Side-LoopNeurons in the Cerebellar Cortex Are Organized into Three LayersSynaptic organization The Purkinje Cells Receive Excitatory Input From Two Afferent Fiber Systems and Are Inhibited by Three Local InterneuronsMossy and Climbing Fibers Encode Peripheral and Descending Information DifferentlyClimbing Fiber Activity Produces Long-Lasting Effects on the Synaptic Efficacy of Parallel FibersFunctional propertyThe Vestibulocerebellum Regulates Balance and Eye MovementsThe Spinocerebellum Regulates Body and Limb MovementsSomatosensory Information Reaches the Spinocerebellum Through Direct and Indirect Mossy Fiber PathwaysThe Spinocerebellum Contains Sensory MapsThe Spinocerebellum Modulates the Descending Motor Systems in the Brain Stem and Cerebral CortexThe Spinocerebellum Uses Feed-Forward Mechanisms to Regulate Movements

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The Cerebrocerebellum Is Involved in Planning Movement and Evaluating Sensory Information for ActionThe Cerebrocerebellum Is Part of a High-Level Internal Feedback Circuit That Regulates Cortical Motor ProgramsLesions of the Cerebrocerebellum Disrupt Motor Planning and Prolong Reaction TimeThe Cerebrocerebellum Also Has Purely Cognitive FunctionsThe Cerebellum Participates in Motor LearningPathology Cerebellar Diseases Have Distinctive Symptoms and Signs