2014 sep 2 cerebellum and its connections
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Transcript of 2014 sep 2 cerebellum and its connections
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Cerebellum and Its Connections-By Mittal Saumya Harsh--September 2, 2014
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FUNCTIONS OF CEREBELLUM
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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
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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.
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GROSS ANATOMY2 large Cerebellar hemispheresSmall Unpaired Median VermisSmall Midline Flocculonodular Lobe
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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
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PHYLOGENETIC DIVISIONS OF CEREBELLUMArchiCerebellum (Oldest)PaleoCerebellum (Relatively small in humans) CorpusNeoCerebellum (Largest subdivision in humans) Cerebelli
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Phylogenetic Divisions Flocculonodular
Lobe◦ ArchiCerebellum
Anterior Lobe◦ PaleoCerebellum
Posterior Lobe◦ NeoCerebellum◦ Middle divisions of
vermis and their lateral extensions.
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ANATOMICAL SUBDIVISIONS OF CEREBELLUMVestibuloCerebellum Ventral Spinocerebellar tractSpinoCerebellumPontoCerebellum Dorsal Spinocerebellar tract
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Same as the flocculonodular lobe
Proprioceptive fibers from the Vestibular nuclei
Functions◦ Eye movement◦ Gross balance
and orientation in space
Vestibulocerebellum
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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
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Pontocerebellum Roughly the
same as neocerebellum
Afferent from pontine nucleus and brachium pontis
Coordination of skilled movements initiated at cerebral cortical levels
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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
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LONGITUDINAL ORGANIZATION OF CEREBELLUMVermian zone,Paravermian zone,Lateral zone
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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
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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
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Paleocerebellum Afferent connections
◦Anterior spinocerebellar tract◦Trigeminocerebellar fibers◦Input from vestibular nucleus◦Corticocerebellar fibers
Efferent connections◦Vestibular nucleus◦Brainstem◦Spinal cord
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Neocerebellum Afferent connections
◦Corticopontine/corticopontocerebellar fibers
◦Spinocerebellar fibers (few)Efferent connections
◦To red nucleus through◦To thalamus Dentate ◦To cerebral cortex Nucleus
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DEEP NUCLEI OF CEREBELLUMDentate nucleusEmboliform nucleusGlobus nucleusFastigial nucleus
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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
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Vermis Fastigial nucleusIntermediate Globose nucleus
Emboliform nucleusLateral Dentate nucleus
Spinocerebellar (Intermediate) have few connections with fastigial nucleus as well
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Fibers from Nuclei
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Therefore, motor control of the
cerebellum is by connection with◦Motor cortex◦Brainstem nuclei◦Descending motor pathways
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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.
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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.
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CEREBELLAR PEDUNCLESSuperior Cerebellar PeduncleMiddle Cerebellar PeduncleInferior Cerebellar Peduncle
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Inferior Cerebellar Peduncle
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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.
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Middle Cerebellar Peduncle
Brachium PontisGreatest peduncleTraversed by
pontocerebellar tracts
Connects cerebral cortices to C/L cerebellar hemisphere
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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.
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Superior Cerebellar Peduncle
Brachium Conjunctivum
Principally efferentChief efferent
fibres◦ Dentatorubral ◦ Dentatothalamic
Also ◦ Anterior
spinocerebellar◦ Cerebellovestibular
tract
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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.
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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.
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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
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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
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Climbing fibers◦Originate in
inferior olivary nucleus.
◦Vine like configuration around Purkinje.
◦Excitatory effect on Purkinje cells.
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CLINICAL FEATURES
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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 .
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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.
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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
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Disorder of equilibrium and gait◦Lesion of anterior vermis
Diminished muscle tone
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SOMATOTOPICAL CEREBELLUMCerebellar cortex (esp. anterior lobe) is somatotopical.
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Sensory map is similar to the motor
map.
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MOLLARET TRIANGLECerebellar-Reticular- Cerebellar Feedback System
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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
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CLINICAL FINDING
SENSORY ATAXIA
CEREBELLAR ATAXIA
Loss of vibration and position sense
+
Areflexia
+
Nystagmus
+
Hypotonia
+
+
Ataxia much worse with eyes closed
+
Past pointing
+
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