CerebellumCerebellum

Dr Taha Sadig Ahmed , MBBS , PhD ( England ) .

Consultant , Clinical Neurophysiology .

Associate Professor , Physiology Department , College of Medicine

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The cerebellum is located at the bottom of the brain , in the posterior cranial fossa , over the occipital bone .It is separated from the overlying cerebrum by a layer of leathery dura mater called Tentorium Cerebelli Anterior to it is Pons and 4th ventricle

4th Ventricle

April 20, 2023April 20, 2023 33Flocculonodular Lobe

Posterolateral Fissure

It consists of (1) two Cerebellar Hemispheres , connected by (2) a middle part called Vermis , and a (3) a posterior Flocculonodular Lobe .

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Flocculonodular Lobe

(1) Neocerebellum ( Cerebrocerebellum )

(2) Spinocerebellum ( Paleocerebellum) , &

(3) Vestibulocerebellum ( Floculonodular Lobe , Archicerebellum )

Neocerebellum

(Lateral parts

of hemispheres )Spinocerebellum

(Vermis + medial parts of

hemispheres)

Hemisphere

Posterolateral Fissure

Functionally , the Cerebellum is divided into 3 parts :

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Inputs to the cerebellumfrom the Cerebrum

Inputs to the Cerebellum from from the Pons

Inputs to the Cerebellum from the Medulla Oblongata

It is connected to the brainstem on each side by 3 peduncles : Superior , Middle & Inferior

Superior C

erebellar

Peduncle

Middle Cerebellar Peduncle

Inferior Cerebellar

Peduncle

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Although it weighs only 10 % as much as the Although it weighs only 10 % as much as the cerebral cortex , its surface area is about 75 % cerebral cortex , its surface area is about 75 % of that of the cerebral cortex .of that of the cerebral cortex .Cerebellar motor pathways are uncrossed, Cerebellar motor pathways are uncrossed, so that injuries on one side will result in so that injuries on one side will result in symptoms & signs on the same side of the symptoms & signs on the same side of the body. body.

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Neocerebellum ) )Cerebrocerebellum(

Comprises the lateral parts of cerebellar hemispheres.It closely cooperates with the cerebrum ( including motor cortex ) cerebral cortex in planning/ in planning/ programming + execution execution of voluntary movements.It is involved in motor learning of voluntary , skilful movements .It coordinates activity of It coordinates activity of muscles involved in muscles involved in execution execution of skilled movements. These skilled movements These skilled movements are mainly performed by are mainly performed by distal limb muscles distal limb muscles ( namely hand muscles ) .( namely hand muscles ) .

Thus the Neocerebellum helps us to monitor ,coordinate , and execute fine , skilled movement ( which is primarily voluntarily initiated by the motor cortex ) .And makes us able to perform complex skilful movements such as writing , drawing , playing musical instruments , singing etc

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Spinocerebellum )Paleocerebellum(

Consist of Vermis & Medial Parts of the Cerebellar Hemispheres .The vemis projects to the brainstem areas concerned with areas concerned with control of axial and proximal limb muscles control of axial and proximal limb muscles (which are (which are concerned with gross postural adjustments ) . concerned with gross postural adjustments ) . The Spinocerebellum receives (1) Proprioceptive inputs afferents from all parts of the body + (2) a copy of the “ Motor Plan ”from the motor cortexIt functions to (1) Regulates & maintains muscle tone (1) Regulates & maintains muscle tone (2) Acts as a comparator(2) Acts as a comparator

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Vestibulocerebellum ( Floculonodular Lobe) It has connections to the vestibular nuclei , consequently , it is concerned with maintenance of body balance & equilibrium It also controls the Vestibulocular Reflex ( VOR)

Efferents from Cerebellar Efferents from Cerebellar CortexCortex

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Neocerebellar Cortical Efferents Neocerebellar Cortical Efferents Neocerebellar cortex projects to to the Neocerebellar cortex projects to to the Dentate Nucleus Dentate Nucleus & from there to the & from there to the Thalamus Thalamus ( its Ventrolateral Nucleus ), ( its Ventrolateral Nucleus ), which , in turn , will project to the which , in turn , will project to the Motor Motor & & Premotor Areas Premotor Areas of the Cerebral Cortex . of the Cerebral Cortex . in order to in order to (1) aid in motor planning(1) aid in motor planning(2) coordinate activity of different muscle groups (2) coordinate activity of different muscle groups during execution of voluntary , skilled movement during execution of voluntary , skilled movement

Spinocerebellar Cortical EfferentsSpinocerebellar Cortical Efferents: : TheThe Vermis projects to the projects to the Fastigial Nucleus Fastigial Nucleus & from there to & from there to Brainstem NucleiBrainstem NucleiThe The Hemispheric Portions of the Spinocerebellum Hemispheric Portions of the Spinocerebellum project to Nucleus Nucleus Interpositus Interpositus ( i.e., ( i.e., Emboliform and Globose nuclei )& from there to & from there to Brainstem Nuclei Brainstem Nuclei These These Brainstem Nuclei Brainstem Nuclei receiving inputs from the receiving inputs from the spinocerebellumspinocerebellum are are concerned with control of axial and proximal limb muscles ( in concerned with control of axial and proximal limb muscles ( in order to adjust muscle tone & body posture ).order to adjust muscle tone & body posture ).

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Vestibulocerebellar Cortical Efferents : Efferents from the Vestibulocerebellum pass directly to Brainstem Nuclei ( & not through the DCN)

These vestibulocerebellar efferents function to regulate of body balance & equilibrium + the VOR ).

Hence , it should be remembered that , though the DCN provide the only outlet for the Neocerebellum and Spinocerebellum , they are not the outlet/gateway for Vestibulocerebellum

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Functions of Functions of Cellular Elements Cellular Elements

of Cerebellar of Cerebellar CortexCortex

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Cerebellar Cellular OrganizationCerebellar Cellular Organization The cerebellum comprises The cerebellum comprises CortexCortex and and Deep Cerebellar Deep Cerebellar Nuclei (DCN) Nuclei (DCN) The The DCN DCN are 4 in number , & are 4 in number , & are named :are named :(1) Dentate , (1) Dentate , (2) Fastigial . (2) Fastigial . (3) Globose , (3) Globose , (4) Emboliform ,(4) Emboliform ,NB : Globosus & Emboliform are NB : Globosus & Emboliform are collectively called collectively called Interpositus Interpositus Nucleus Nucleus ..

Cerebellar Afferents : Cerebellar Afferents : These are These are Mossy Fibers Mossy Fibers & & Climbing Climbing Fibers Fibers . . Climbing Fibers Climbing Fibers come from come from the the Inferior Olivary Nucleues Inferior Olivary Nucleues , & they , & they provide provide indirectindirect proprioceptive proprioceptive inputsinputs to the cerebellar cortex to the cerebellar cortex

Mossy Fibers, come from (1) all parts of the body , + (2) cerebral cortex . As they ascend , they send collaterals to the DCN , and thereafter proceed ( pass on ) to synapse on cerebellar cortical cells .

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Layers of the Cerebellar CortexLayers of the Cerebellar Cortex

The cerebellar cortex The cerebellar cortex is made of layers is made of layers

))11 ( (External External Molecular layerMolecular layer , ,

) )22 ( (Middle Purkinje Middle Purkinje Cell layer that isCell layer that is

only one cell thickonly one cell thick , ,

))33 ( (Internal Granular Internal Granular layerlayer

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The cerebellar cortex contains mainly 5 types of neurons : Purkinje , The cerebellar cortex contains mainly 5 types of neurons : Purkinje ,

Granule , Basket , Stellate & Golgi cells .Granule , Basket , Stellate & Golgi cells .

(1) Purkinje Cells :(1) Purkinje Cells : Are amongst the biggest neurons in the body .Are amongst the biggest neurons in the body .

Have very extensive dendritic arbors that extend throughout the Molecular Have very extensive dendritic arbors that extend throughout the Molecular Layer .Layer .

Their axons , which are the only output from the cerebellar cortex , pass to Their axons , which are the only output from the cerebellar cortex , pass to the deep nuclei . the deep nuclei .

Cells of Cells of the the

Cerebellar Cerebellar

CortexCortex

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))22 ( (Granule CellsGranule Cells Their cell-bodies are situated in the Granular layer .Their cell-bodies are situated in the Granular layer .

They receive inputs from the Mossy fibers and they innervate the They receive inputs from the Mossy fibers and they innervate the Purkinje cells . Purkinje cells .

Each sends an axon to the Molecular layer , where the axon Each sends an axon to the Molecular layer , where the axon bifurcates to form a T . bifurcates to form a T .

Because the branches of this “ T ” are straight and run for long Because the branches of this “ T ” are straight and run for long distances , they are called Parallel Fibers .distances , they are called Parallel Fibers .

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The other 3 types of neurons in the cerebellar cortex are inhibitory The other 3 types of neurons in the cerebellar cortex are inhibitory neurons :neurons :

(3) Basket cells :(3) Basket cells :Are located in the Molecular layer Are located in the Molecular layer

They receive inputs from Parallel fibers , and each projects to many They receive inputs from Parallel fibers , and each projects to many Purkinje cells .Purkinje cells .

Their axons form a basket around the cell-body and axon hillock of Their axons form a basket around the cell-body and axon hillock of each Purkinje cell they innervate .each Purkinje cell they innervate .

They are excited by Parallel fibers of Granule cells , & their output They are excited by Parallel fibers of Granule cells , & their output inhibits Purkinje cell discharge by a process of inhibits Purkinje cell discharge by a process of Feed-Forward Feed-Forward Inhibition . Inhibition .

(4) Stellate cells (4) Stellate cells Similar to Basket cells , these cells are excited by Parallel fibers of Similar to Basket cells , these cells are excited by Parallel fibers of Granule cells , & their output inhibits Purkinje cell discharge by a Granule cells , & their output inhibits Purkinje cell discharge by a process of process of Feed-Forward Inhibition . Feed-Forward Inhibition .

They differ from Basket cells only in being more superficially They differ from Basket cells only in being more superficially located in the cortex than Basket cells .located in the cortex than Basket cells .

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Golgi cells are located in the Granular layer . Golgi cells are located in the Granular layer . Their dendrites , which project into the Molecular layer Their dendrites , which project into the Molecular layer , receive inputs from the Parallel fibers . , receive inputs from the Parallel fibers . Their cell bodies receive input via collateralsfrom the Their cell bodies receive input via collateralsfrom the incoming Mossy fibers and the Purkinje cells incoming Mossy fibers and the Purkinje cells Their axons project to the dendrites of the Granule Their axons project to the dendrites of the Granule cells . cells . They are excited by They are excited by

(1) Mossy fibers(1) Mossy fibers(2) Purkinje cells , &(2) Purkinje cells , &(3) Parallel fibers .(3) Parallel fibers .

They inhibit the action of Mossy fibers on Granule They inhibit the action of Mossy fibers on Granule cells . cells .

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The Main Inputs The Main Inputs (Afferents ) to the Cerebellar (Afferents ) to the Cerebellar

Cortex (1)Cortex (1)

There are 2 main inputs to the There are 2 main inputs to the cerebellar cortex : the Climbing cerebellar cortex : the Climbing Fibers and Mossy Fibers , Fibers and Mossy Fibers , both of both of which are excitatory .which are excitatory .

Climbing Fibers : Climbing Fibers : The climbing fibersThe climbing fibers come come solelysolely from the from the Inferior Olivary NucleuesInferior Olivary Nucleues They provide an They provide an indirectindirect proprioceptive inputproprioceptive input to the to the cerebellar cortex cerebellar cortex bringing to it bringing to it proprioceptive information from all proprioceptive information from all parts of the body via relays in the parts of the body via relays in the Inferior Olive Inferior Olive (which receives (which receives proprioceptive inputs from all over proprioceptive inputs from all over the body parts )the body parts )

Each climbing fiber projects to Each climbing fiber projects to the dendrites of Purkinje cells , the dendrites of Purkinje cells , around which it entwines like a around which it entwines like a climbing plant .climbing plant .

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The Main Inputs The Main Inputs (Afferents ) to the Cerebellar Cortex (2)(Afferents ) to the Cerebellar Cortex (2)

Mossy Fibers : Mossy Fibers : (1) These , unlike Climbing Fibers (1) These , unlike Climbing Fibers

( which provide an indirect ( which provide an indirect proprioceptive input ) do provide a proprioceptive input ) do provide a directdirect proprioceptive pathway proprioceptive pathway ( input )( input ) to the cerebellar cortex , to the cerebellar cortex , from all parts of the body , and , in from all parts of the body , and , in addition addition (2) Provide inputs from the(2) Provide inputs from the Motor Motor Area ( M1) & related areas Area ( M1) & related areas of theof the Cerebral CortexCerebral Cortex ( indirectly , via ( indirectly , via relays in the pontine nuclei ).relays in the pontine nuclei ).They end on the dendrites of They end on the dendrites of Granule cells in complex synaptic Granule cells in complex synaptic groupings called groupings called GlomeruliGlomeruli . .The Glomeruli also contain the The Glomeruli also contain the inhibitory endings of the Golgi inhibitory endings of the Golgi cells.cells.

Climbing Fibers Mossy Fibers

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Corollary ) summary ( of effects of different cells & Corollary ) summary ( of effects of different cells & afferents on Purkinje cellsafferents on Purkinje cells

(A) Excitatory (A) Excitatory The fundamental circuits of cerebellar cortex are thus relatively simple : The fundamental circuits of cerebellar cortex are thus relatively simple :

(1) (1) climbing fiberclimbing fiber inputs exert a inputs exert a strong excitatorystrong excitatory effect on effect on singlesingle Purkinje Purkinje cells , whereas cells , whereas

(2) (2) Mossy fiberMossy fiber inputs exert ainputs exert a weak excitatoryweak excitatory effect oneffect on manymany Purkinje cellsPurkinje cells via the Granule cells .via the Granule cells .

(B) Inhibitory (B) Inhibitory (1) Basket cells (1) Basket cells (2) Stellate cells (2) Stellate cells (3) Golgi cells(3) Golgi cells

Golgi cells are excited by Golgi cells are excited by (1) Mossy fibers(1) Mossy fibers(2) Purkinje cells , &(2) Purkinje cells , &(3) Parallel fibers .(3) Parallel fibers .

They inhibit the action of Mossy fibers on Granule cellsThey inhibit the action of Mossy fibers on Granule cells

Both are excited by Parallel fibers of Granule Both are excited by Parallel fibers of Granule cells , & their output inhibits Purkinje cellscells , & their output inhibits Purkinje cells

) ) Feed-Forward Inhibition ( .Feed-Forward Inhibition ( .

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Q : What are the Neurotransmitters Secreted by in Q : What are the Neurotransmitters Secreted by in the Cerebellar Cortex Neuronsthe Cerebellar Cortex Neurons ? ?

Purkinje cellsPurkinje cells

Basket cellsBasket cells

Stellate cellsStellate cells

Golgi cellsGolgi cells

Granule cells Granule cells Glutamate Glutamate

Secrete GABA

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Summary of Connections & FunctionsSummary of Connections & Functions DeepDeep

NucleiNucleiCortexCortexInputsInputsOutputsOutputsFunctionFunction

Neo-Neo-

cerebellucerebellumm

DentateDentateLateral Lateral portions of portions of Cerebellar Cerebellar HemisphereHemisphere

CorticopontinCorticopontine/e/

pontocerebellpontocerebellarar

SCP to SCP to VA/VLVA/VL

In cooperation In cooperation with cerebral with cerebral cortex cortex Planning , Planning , orogramming and orogramming and execution of execution of voluntary & skilled voluntary & skilled movementsmovements

Spino-Spino-

cerebellucerebellumm

InterposeInterposed; d; FastigialFastigial

Vermis & Vermis & Medial Medial portions of portions of Cerebellar Cerebellar hemisphereshemispheres

Spinal and Spinal and brainstem brainstem pathspaths

SCP to Red SCP to Red Nucleus; Nucleus; Fastigial to Fastigial to RFRF

(1) Muscle tone(1) Muscle tone

(2) Postural (2) Postural adjustmen&adjustmen&

(3) Coordination(3) Coordination

of differentof different

muscle groupsmuscle groups

activity foractivity for

smoothsmooth

performance of performance of

movementmovement

Vestibulo-Vestibulo-

cerebellucerebellumm

FastigialFastigialFlocculoFlocculo

Nodular LobeNodular LobeVestibular Vestibular nucleinuclei

Vestibular Vestibular nuclei; RFnuclei; RF

Balance , Balance , equilibrium & VORequilibrium & VOR

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Summary of Cerebellar Cortex EfferenrtsSummary of Cerebellar Cortex Efferenrts

Projections of Neocerebellar Cortex :Projections of Neocerebellar Cortex :The Neocerebellar Cortex projects ( sends its efferents ) to the The Neocerebellar Cortex projects ( sends its efferents ) to the Dentate NucleusDentate Nucleus & from there to the Ventrolateral Nucleus of & from there to the Ventrolateral Nucleus of the Thalamus .the Thalamus .Projections of Spinocerebellar Cortex :Projections of Spinocerebellar Cortex : The The medial part of the Spinocerebellum medial part of the Spinocerebellum ( Vermis )( Vermis ) projects to projects to the Fastigial Nuclei the Fastigial Nuclei & from there to the brainstem . & from there to the brainstem .The The hemispheric portions of the Spinocerebellum hemispheric portions of the Spinocerebellum ( i.e., ( i.e., medial parts of the cerebellar hemispheres ) project to the Emboliform and Globose nuclei & from there to the brainstem nuclei . & from there to the brainstem nuclei .Projections of the Vestibulocerebellar Cortex :Projections of the Vestibulocerebellar Cortex : Most of the Most of the VestibulocerebellumVestibulocerebellum cortex outputs ( efferents ) cortex outputs ( efferents ) pass directly to the brainstem ( to regulate balance , equilibrium pass directly to the brainstem ( to regulate balance , equilibrium & the VOR ).& the VOR ).However , unlike it , the rest of the cerebellar cortex ( i.e., that However , unlike it , the rest of the cerebellar cortex ( i.e., that of the of the Neocerebellum Neocerebellum and and SpinocerebellumSpinocerebellum ) sends fibers first ) sends fibers first to the deep cerebellar nuclei , and then , these in turn will to the deep cerebellar nuclei , and then , these in turn will project ( send their efferents ) to the brainstem .project ( send their efferents ) to the brainstem .Consequently , the Consequently , the Deep Cerebellar NucleiDeep Cerebellar Nuclei provide the only provide the only output of the Neocerebellum and Spinocerebellum .output of the Neocerebellum and Spinocerebellum .

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SummarySummary The cerebellum influences movement on the The cerebellum influences movement on the ipsilateralipsilateral side side of the body.of the body.

NeocerebellumNeocerebellum is involved , in conjunction & close is involved , in conjunction & close cooperation with cooperation with the cerebral cortex the cerebral cortex , in programming , , in programming , planning & execution of voluntary movement ; planning & execution of voluntary movement ; especially especially skilled movements ( which is mostly performed by the distal skilled movements ( which is mostly performed by the distal limb muscles ( e.g., hand )limb muscles ( e.g., hand )

SpinocerebellumSpinocerebellum is primarily involved with (1) regulation & is primarily involved with (1) regulation & maintenance of muscle tone , (2) gross postural adjustments , & (3) coordination between different muscle groups for smoothening of movement ( it acts as a comparator )

(The vermis helps coordinate movements of the (The vermis helps coordinate movements of the axial and proximal limb muscles ) ..Floculonodular lobeFloculonodular lobe is mainly concerned with balance is mainly concerned with balance equilibrium as well as VOR .equilibrium as well as VOR .

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Contd SummaryContd Summary..…… ..…… Climbing fibers originate in the inferior olivary Climbing fibers originate in the inferior olivary nuclei and synapse directly onto Purkinje cells.nuclei and synapse directly onto Purkinje cells.

All other sources of input to the cerebellum enter All other sources of input to the cerebellum enter as mossy fibers.as mossy fibers.

Purkinje cells are the main output neurons of the Purkinje cells are the main output neurons of the cerebellar cortex & project to the deep nuclei of cerebellar cortex & project to the deep nuclei of the cerebellum.the cerebellum.

They are inhibitory to the DCN .They are inhibitory to the DCN .

The deep cerebellar nuclei ( DCN ) project out The deep cerebellar nuclei ( DCN ) project out to brainstem and thalamic targets via the to brainstem and thalamic targets via the superior cerebellar peduncles. They are superior cerebellar peduncles. They are excitatory , but in turn , are themselves inhibited excitatory , but in turn , are themselves inhibited ( switched off ) by Purkinje cells .( switched off ) by Purkinje cells .

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Cerebellar Cerebellar SyndromeSyndrome

ss

Signs of Cerebellar Disorders

Deficit Manifestation

AtaxiaReeling, wide-based gait

Decomposition ofmovement

Inability to correctly sequence fine, coordinated acts

DysarthriaInability to articulate words correctly, with slurring and inappropriate phrasing

DysdiadochokinesiaInability to perform rapid alternating movements

DysmetriaInability to control range of movement

HypotoniaDecreased muscle tone

NystagmusInvoluntary, rapid oscillation of the eyeballs in a horizontal,

vertical, or rotary direction, with the fast component maximal

toward the side of the cerebellar lesion

Scanning speechSlow enunciation with a tendency to hesitate at the beginning

of a word or syllable

TremorRhythmic, alternating, oscillatory movement of a limb as it

approaches a target (intention tremor) or of proximalmusculature when fixed posture or weight bearing is

attempted(postural tremor)

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The Difference Between Lesions of the Cerebellar Cortex & Lesions of DCN

If only the cortex of the cerebellum is involved , If only the cortex of the cerebellum is involved , the movement abnormalities gradually disappear the movement abnormalities gradually disappear as as “ compensation ”“ compensation ” occurs . occurs .However , lesions of the DCN produce more However , lesions of the DCN produce more generalized defects , and abnormalities are generalized defects , and abnormalities are permanent .permanent .For this reason , care should be taken to avoid For this reason , care should be taken to avoid damaging the DCN when surgery is undertaken damaging the DCN when surgery is undertaken to remove a tumor involving part of the to remove a tumor involving part of the cerebellar cortex .cerebellar cortex .

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Cerebellar Hemispheric LesionsCerebellar Hemispheric Lesions Cerebellar lesions cause no paralysis or sensory Cerebellar lesions cause no paralysis or sensory deficit . deficit . When not moving , there are no externally When not moving , there are no externally obvious signs . obvious signs . However , upon physical examination , signs However , upon physical examination , signs such as hypotonia and pendular reflexes can be such as hypotonia and pendular reflexes can be elicited .elicited .Once the patients attempts movement , ataxia Once the patients attempts movement , ataxia appears .appears .What is ataxia ? Ataxia is incoordination of due to What is ataxia ? Ataxia is incoordination of due to errors in the rate , range , force and direction of errors in the rate , range , force and direction of movement .movement .Wth circumscribed lesions , the ataxia may be Wth circumscribed lesions , the ataxia may be confined/localized to only one part of the body .confined/localized to only one part of the body .

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I/Ataxia (lack of coordination of muscle I/Ataxia (lack of coordination of muscle movement ) , which is manifested by movement ) , which is manifested by (1) Wide-based , unsteady “ drunken , or (1) Wide-based , unsteady “ drunken , or staggering “ gait .staggering “ gait .(2) Scanning speech (2) Scanning speech (3) Dysmetria(3) Dysmetria ( also called ( also called Past-Pointing Past-Pointing ) : ) : attempting to touch an object with a finger attempting to touch an object with a finger results in overstretching to one side or the results in overstretching to one side or the otherother this promptly initiates a gross correction this promptly initiates a gross correction action ( corrective action ) , but the correction action ( corrective action ) , but the correction overshoots to the other side overshoots to the other side Consequently , Consequently , the finger oscillates back and forth . the finger oscillates back and forth . This oscillation is the (4) “ Intention Tremor ” , This oscillation is the (4) “ Intention Tremor ” , which is characteristic of cerebellar disease . which is characteristic of cerebellar disease . This cerebellar tremor , unlike that of This cerebellar tremor , unlike that of Parkinson’s disease , is absent at rest .Parkinson’s disease , is absent at rest .

A/ Hemispheric Lesions

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II/ Inability to “ put on the brakes ” II/ Inability to “ put on the brakes ” i.e., inability to stop i.e., inability to stop movement promptly . Normally , for example , flexion of movement promptly . Normally , for example , flexion of the forearm against resistance is quickly checked when the forearm against resistance is quickly checked when the resistance force is suddenly broken off . The patient the resistance force is suddenly broken off . The patient with cerebellar disease can not break the movement of with cerebellar disease can not break the movement of the limb , and the forearm flies back in a wide arc . This the limb , and the forearm flies back in a wide arc . This abnormal response is known as the “ abnormal response is known as the “ Rebound Rebound Phenomenon ”. Phenomenon ”. III/ III/ Adiadochkinesia ( Dysdiadochkinesia )Adiadochkinesia ( Dysdiadochkinesia ) : Inability to : Inability to perform rapidly alternating opposite movements such as perform rapidly alternating opposite movements such as repeated pronation and supination of the hands .repeated pronation and supination of the hands .IV/ Difficulty in performing actions that involve IV/ Difficulty in performing actions that involve simultaneous motions at more than one joint . The simultaneous motions at more than one joint . The patient dissects such movements and carries them out patient dissects such movements and carries them out one joint at a time , a phenomenon known as one joint at a time , a phenomenon known as “ “ Decomposition of Movement ”Decomposition of Movement ” . .

Hemispheric Lesions ( Contd )

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B/ Flocculonodular Lobe LesionsB/ Flocculonodular Lobe Lesions Midline cerebellar tumors in children , arising Midline cerebellar tumors in children , arising from the “ Nodule ” , early in their course from the “ Nodule ” , early in their course

(& before affecting the rest of the cerebellum) , (& before affecting the rest of the cerebellum) , damage first the Flocculonodular lobe . damage first the Flocculonodular lobe .

Such a child is afraid ( & reluctant ) to stand Such a child is afraid ( & reluctant ) to stand erect and move without support .erect and move without support .

This is because if he tries to walk , he does so in This is because if he tries to walk , he does so in a staggering fashion on a broad base , & tends a staggering fashion on a broad base , & tends to fall . to fall .

Moreover , selective Flocculonodular lobe Moreover , selective Flocculonodular lobe lesions may cause vertigolesions may cause vertigo

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Role of the Cerebellum in Learning (1)Role of the Cerebellum in Learning (1)

The cerebellum is concerned with learned adjustments that make coordination easier when a given task is performed over & over As a motor task is learned , activity in the brain shifts from the Prefrontal ( cerebral ) Cortex to the (1) Parietal Cortex , (2) M1 , & (3) Cerebellum . The basis of learning in the cerebellum is the input via the Olivary Nucleus.It is worth noting , in this regard , that each Purkinje cell receives inputs from 250,000 to 1,000,000 Mossy fibers. By contrast , each Purkinje cell receives only a single ( only one ) Climbing fiber from the inferior olive , and this fiber makes 200-3000 synapses on the Purkinje cell . Climbing fiber activation produces a large complex spike in the Purkinje cell This spike produces lomg-term modification of the pattern of Mossy fiber input to that particular Purkinje cell. Climbing fiber activity is increased when a new movement is being learned , and lesions of the Olivary Nucleus abolish the ability to produce long-term adjustments in motor responses . .

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Finished Finished