Cerebellum and Its Connections-By Mittal Saumya Harsh--September 2, 2014

FUNCTIONS OF CEREBELLUM

Functions of CerebellumPrincipally a motor organ responsible

for◦Coordination of movements esp skilled

movements◦Control of posture, gait and tone◦Initiation and modulation of willed

movements generated in cerebrumMotor activities don’t reach conscious

kinesthetic perception.May modulate emotional state and

cognition

In the words of Gordon Holmes, lesions of cerebellum, do not cause weakness, but rather loss of coordination and inability to gauge and regulate the “rate, range and force” of movement.

GROSS ANATOMY2 large Cerebellar hemispheresSmall Unpaired Median VermisSmall Midline Flocculonodular Lobe

Three Parts-

◦ Cerebellar hemispheres Appendicular

coordination

◦ Vermis Connection between

hemispheres Gait and axial function

◦ Flocculonodular lobe Paired lateral flocculi

with midline nodulus Eye movements &

balance

Cerebellar tonsils- small, rounded lobules on inferior aspects of cerebellar hemispheres, just above the foramen magnum

PHYLOGENETIC DIVISIONS OF CEREBELLUMArchiCerebellum (Oldest)PaleoCerebellum (Relatively small in humans) CorpusNeoCerebellum (Largest subdivision in humans) Cerebelli

Phylogenetic Divisions Flocculonodular

Lobe◦ ArchiCerebellum

Anterior Lobe◦ PaleoCerebellum

Posterior Lobe◦ NeoCerebellum◦ Middle divisions of

vermis and their lateral extensions.

ANATOMICAL SUBDIVISIONS OF CEREBELLUMVestibuloCerebellum Ventral Spinocerebellar tractSpinoCerebellumPontoCerebellum Dorsal Spinocerebellar tract

Same as the flocculonodular lobe

Proprioceptive fibers from the Vestibular nuclei

Functions◦ Eye movement◦ Gross balance

and orientation in space

Vestibulocerebellum

Spino/Paleocerebellum (evolved when extremity control was not a concern)

Anterior and part of Posterior Vermis (and paravermal cortex)

Proprioceptive fibers from muscles and tendons of limbs

Functions◦ Influence posture, ◦ muscle tone, ◦ axial muscle control, ◦ locomotion

Dorsal Spinocerebellar Tract from lower limbs

Ventral Spinocerebellar tract from upper limbs

Pontocerebellum Roughly the

same as neocerebellum

Afferent from pontine nucleus and brachium pontis

Coordination of skilled movements initiated at cerebral cortical levels

These divisions are incomplete. It

is now appreciated that certain portions of cerebellar hemispheres are also involved in other functions e.g.◦Tactual◦Visual ◦Auditory◦Visceral

LONGITUDINAL ORGANIZATION OF CEREBELLUMVermian zone,Paravermian zone,Lateral zone

Functions of Longitudinal Divisions ◦ Vermian (median)

Coordinates movements of eyes and body with respect to gravity

Coordinates movement of head in space

◦ Paravermian (intermediate) Influences postural tone Influences individual movements of individual limbs

◦ Lateral Coordination of movements of ipsilateral limbs Other functions

Flocculonodular LobeConnections are toAfferent

◦ Labyrinths◦ Vestibular centers◦ Spinal cord◦ Brainstem◦ Reticular formation◦ Olivary bodies

Efferent◦ Vestibular nuclei◦ Vestibulospinal tract ◦ Reticular formation

The manifestations are difficult to separate from invariably involved vestibular findings.

Isolated FN lobe dysfunction is usually seen in children in-EpendymomasMedulloblastom

as

Paleocerebellum Afferent connections

◦Anterior spinocerebellar tract◦Trigeminocerebellar fibers◦Input from vestibular nucleus◦Corticocerebellar fibers

Efferent connections◦Vestibular nucleus◦Brainstem◦Spinal cord

Neocerebellum Afferent connections

◦Corticopontine/corticopontocerebellar fibers

◦Spinocerebellar fibers (few)Efferent connections

◦To red nucleus through◦To thalamus Dentate ◦To cerebral cortex Nucleus

DEEP NUCLEI OF CEREBELLUMDentate nucleusEmboliform nucleusGlobus nucleusFastigial nucleus

Structure of cerebellumCerebellum is a composite of

◦White matter core◦Grey matter thin cortex◦Cerebellar nuclei- deep grey matter

structuresNuclei

◦Dentate nucleus◦Emboliform nucleus nucleus◦Globose nucleus interpositus◦Fastigial nucleus

Vermis Fastigial nucleusIntermediate Globose nucleus

Emboliform nucleusLateral Dentate nucleus

Spinocerebellar (Intermediate) have few connections with fastigial nucleus as well

Fibers from Nuclei

Therefore, motor control of the

cerebellum is by connection with◦Motor cortex◦Brainstem nuclei◦Descending motor pathways

Functions of Deep Nuclei

Dentate Nucleus Fastigial Nucleus

Receives fibers from-◦ Premotor cortex.

◦ Supplementary motor cortex.

Initiate volitional movements.

Inactivation of dentate nucleus delayed initiation of such movement.

Controls antigravity muscles and other muscle synergies in standing and walking.

Nuclei Interpositus Prepositus Nucleus

Cerebrocortical projections via pontocerebellar system.

Spinocerebellar projections ◦ Information from Golgi

tendon organs, muscle spindles, cutaneous afferents, subcutaneous interneurons.

◦ Fires when movement has started.

◦ Dampens physiological tremors- Intention tremors if interrupted

Known to be neural integrator of horizontal eye movements.

May also function in postural balance in view of its connections with vestibular nuclei and vestibulocerebellum.

Responsible for volitional oscillations.

CEREBELLAR PEDUNCLESSuperior Cerebellar PeduncleMiddle Cerebellar PeduncleInferior Cerebellar Peduncle

Inferior Cerebellar Peduncle

Posterior spinocerebellar tract, originates from posterior nucleus. Carries proprioceptive and exteroceptive information from trunk and I/L lower limbs.

The cuneocerebellar tract, originating in the external arcuate nucleus transmits proprioceptive information from the upper extremity and neck.

The olivocerebellar tract carries somatosensory information from the contralateral inferior olivary nuclei.

The vestibulocerebellar tract transmits information from vestibular receptors on both sides of the body.

The reticulocerebellar tract arises in the lateral reticular and paramedian nuclei of the medulla.

The arcuatocerebellar tract arises from the arcuate nuclei of the medulla oblongata.

The trigeminocerebellar tract arises from the spinal and main sensory nuclei of the trigeminal nerve.

Middle Cerebellar Peduncle

Brachium PontisGreatest peduncleTraversed by

pontocerebellar tracts

Connects cerebral cortices to C/L cerebellar hemisphere

Pontocerebellar

(corticopontocerebellar) tract arises in the contralateral pontine gray matter and transmits impulses from the cerebral cortex to the intermediate and lateral zones of the cerebellum.

Superior Cerebellar Peduncle

Brachium Conjunctivum

Principally efferentChief efferent

fibres◦ Dentatorubral ◦ Dentatothalamic

Also ◦ Anterior

spinocerebellar◦ Cerebellovestibular

tract

Afferent fibres include◦The ventral spinocerebellar tract transmits

proprioceptive and exteroceptive information from levels below the midthoracic cord.

◦The tectocerebellar tract, arising in the superior and inferior colliculi carries auditory and visual information.

◦The trigeminocerebellar tract carries proprioceptive fibers from the mesencephalon and tactile information from the chief sensory nucleus of the trigeminal nerve.

◦The cerulocerebellar tract carries fibers from the nucleus ceruleus.

Efferent fibers include◦The dentatorubral tract carries

output to the contralateral red nucleus. Many of the fibers ending in this nucleus are branches of the larger dentatothalamic tract.

◦The dentatothalamic tract transmits output to the contralateral ventrolateral nucleus of the thalamus.

NEURONAL ORGANIZATION3 layered structure that has 5 types of neuronsMolecular layer- Stellate cells, Basket cells- inhibitory Layer of Purkinje cells (inhibitory)- GABAGranular layer- Granule cells (excitatory), Golgi

interneurons

3 types of fibres of cortexParallel fibres-

◦ From granule cells◦ Along long axis◦ Excite the Purkinje cells in

a Million: One ratio◦ Excite the Stellate and

Basket cells that inhibit Purkinje cells

Mossy fibres- ◦ From spinocerebellar,

pontine, vestibular and reticular nuclei.

◦ End in granule layer◦ Excitatory

Climbing fibers◦Originate in

inferior olivary nucleus.

◦Vine like configuration around Purkinje.

◦Excitatory effect on Purkinje cells.

CLINICAL FEATURES

Normal MovementPerformance of a normal

movement needs-◦To begin movement-

Contraction of agonists, with relaxation/modified tone of antagonist.

Synergist reinforce the movement. Fixating muscles prevent displacement

and maintain tone and posture

◦To end movement- Contraction of antagonist, with agonist

relaxation .

Lesions in Cerebellum cause

Incoordination◦Speed of initiation of movement is slowed.◦ Irregularity and slowing of movement itself.◦Excursion of limb arrested prematurely (short

agonist burst).◦The limb overshoots the mark- hypermetria

(long agonist burst).Tremor

◦The intention or action tremor of finger Is chiefly instability of shoulder Tremor is perpendicular to trajectory.

All defects of volitional control are evident on rapid alternating movements- adiadochokinesis.

Coarse tremors◦ Wing beating tremor◦ Titubation (AP plane)

Altered Ocular movement ◦ Nystagmus◦ Skew deviation◦ Ocular flutter◦ Ocular myoclonus

Disorder of speech◦ Slurring dysarthria◦ Scanning dysarthria

Disorder of equilibrium and gait◦Lesion of anterior vermis

Diminished muscle tone

SOMATOTOPICAL CEREBELLUMCerebellar cortex (esp. anterior lobe) is somatotopical.

Sensory map is similar to the motor

map.

MOLLARET TRIANGLECerebellar-Reticular- Cerebellar Feedback System

Superior Cerebellar Peduncle

Decussate

Central Tegmental Fasciculus

Venteromedial Tegmentum of Brainstem

1. Inferior Olivary Nuclei of Medulla2. Reticulotegmental nuclei of pons

3. Paramedian reticular nuclei of pons

Inferior Cerebellar Peduncle

Anterior Lobe of Cerebellum

 CLINICAL FINDING

 SENSORY ATAXIA

 CEREBELLAR ATAXIA

 Loss of vibration and position sense

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 Areflexia

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 Nystagmus

  

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 Hypotonia

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 Ataxia much worse with eyes closed

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 Past pointing

  

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