lect 4 cerebellum improved

7/29/2019 Lect 4 Cerebellum Improved

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CEREBELLUM Largest part of hind

brain.

LOCATION:

Posterior cranial

fossa behind pons &

medulla.

ANATOMY: Covered

above by meninges(Tentorium

Cerebelli).

Has 2 hemispheres

joined by Vermis.


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LOBES: 3

1) anterior lobe

2) posterior / middlelobe

3) flocculo nodular lobe

FISSURES: 2

1) Primary fissure (vshaped). Part ofcerebellum above thisfissure is anterior lobe.

2) Uvulo-nodular fissure(separates posteriorlobe from flocculonodular lobe)


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Topographical representation: Vermis &

Intermediate zone of cerebellar

hemisphere.

Each cerebellar hemisphere has 2 zones,

intermediate zone & lateral zone.

Axial parts of body represented in

Vermis.

Limbs & facial region Intermediate

zone.


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AFFERENTS TO TOPOGRAPHICALREPRESENTATION:

Corresponding areas of motor cortex.

Corresponding parts of the body &

Brain stem

EFFERENTS:

Cerebral cortex Red nucleus

Reticular formation


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VERMIS: 10 Primary lobules.


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I LINGULA

II CENTRAL LOBULE

III CENTRAL LOBULE

IV CULMEN

V DECLIVE

VI SIMPLE LOBULE

VII FOLIUM TUBER.

VIII PYRAMID

IX UVULA

X NODULE


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Cerebellum has:

1) cortex cerebellar (grey matter on periphery)

2) white matter core (having deep cerebellarnuclei, 4 on each side, from lateral to medialside:

DENTATE, EMBOLIFORM, GLOBASE &FESTIGEAL. (Lateral medial) BUT DEGF! (dont eat greasy food)

EMBOLIFORM + GLOBASE = NUCLEUS

INTERPOSITUS.


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MOTOR OUTPUT FROMCEREBELLUM: Axons of neurons in deep cerebellar

nuclei motor output.

From dentate + interpositus leave via

SUPERIOR CEREBELLAR PEDUNCLE.

From fastigial nucleus leave via

INFERIOR CEREBELLAR PEDUNCLE.


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F G E D

( N.I)

SUPERIOR

CEREBELLAR PEDUNCLE

INFERIOR

CEREBELLAR PEDUNCLE


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CEREBELLAR CORTEX: 3 LAYERS:

Outermost molecular layer

2nd layer purkinje cells layer

3rd later granular layer

PURKINJE

CELL

AXONS

DENDRITES


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MOLECULAR LAYER: STELLATE CELLS

BASKET CELLS

Large no. ofdendrites & nerve

fibers from deeper

layers.


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PURKINJE CELL LAYER: Single layer. Flask shaped cells.

From top of cells arise dendrites 1, 2 (withoutdendritic spines, i.e., smooth)

& 3 branches (with dendrite spines).

From base of cells axons white matter acquiresmyelin sheath.

Most nerve fibers from purkinje cells

synapse onto

deep nuclear cells.

Only few fibers bypass deep nuclear cells go tovestibular nuclei.


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GRANULAR LAYER: Granule cells having Multiple dendrites

synapse with incoming

Mossy fibers.

Their axons pass into

molecular layer

end into a T termination.

These fibers alsosynapse with golgi cells,

basket cells & stallate

cells.


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WHITE MATTER OFCEREBELLUM: 3 TYPES OF FIBERS:

INTRINSIC FIBERS

AFFERENT FIBERS

EFFERENT FIBERS


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INTRINSIC FIBERS: Pass between cerebellar cortex & vermis.

Also pass from 1 cerebellar hemisphere

to other. They remain in the cerebellum.


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AFFERENT FIBERS: 2 TYPES:

CLIMBING FIBERS (come from inferior

olivary nucleus) MOSSY FIBERS (all the other afferent

fibers except the climbing are called

Mossy fibers).


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EFFERENT FIBERS: Start as axons of purkinje cells.

Most of these axons synapse onto deep

nuclear cells.

From deep nuclear cells, efferent fibers arise

go to different parts of CNS .

Only few purkinje fibers bypass deep nuclear

cells go to vestibular nuclei (these are from

vermis & flocculo-nodular lobe).


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There is a neuronal circuit in cerebellum.

Millions of functional units.

Each functional unit consist of a purkinje cell &a deep nuclear cell.

Climbing fibers give collaterals, which synapsewith deep nuclear cells.

collaterals from climbing fibers excite deepnuclear cells.

Climbing fibers pass to molecular layersynapse with dendrites ofpurkinje cells.


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Mossy fibers collaterals synapsewith deep nuclear cells.

Mossy fibers granular layersynapse with dendrites of granule cell.

1 climbing fibercan synapse with about 10 purkinje cells.

1 mossy fibercan synapse with 100s ofgranule cells.


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Excitatory:

deep nuclear cells Granule cells

Inhibitory:

Purkinje cells

Basket cells

Golgi cells

Stellate cells


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When deep nuclear cells are to be excited, itsthrough COLLATERALS from climbing &mossy fibers.

When inhibited, its through purkinje cells.

Purkinje cells & deep nuclear cells discharge

continuously (50-100 impulses/sec).

This is the neuronal circuit in the cerebellum.


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BASIC FUNCTION OF CEREBELLUM: To control timing of turn-on signals to agonists

& turn-off signals to antagonists at the onset ofa movement & then

To control timing of turn-off signal to agonists &turn-on signals to antagonists at the end of a

movement.

Basic disturbance in cerebellar disease

ATAXIA / INCOORDINATION OF

MOVEMENT.


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CONNECTIONS OF CEREBELLUMTHROUGH 3 PEDUNCLES: AFFERENT

EFFERENT

Superior peduncle

midbrainMiddle peduncle

pons

Inferior peduncle

medulla


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INFERIOR CEREBELLAR PEDUNCLECONNECTIONS: AFFERENTS:

Posterior spino-cerebellar tract.

Cuneo-cerebellar tract (from cuneate nucleus).

Vestibulo-cerebellar fibers (from vestibular

nuclei).

Reticulo cerebellar (from reticular formation).

Olivo-cerebellar (from inferior olivary nucleus).


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EFFERENTS:

Cerebello-vestibular

Cerebello-reticular


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MIDDLE PEDUNCLE:Mainly AFFERENTS (Ponto-cerebellar

fibers).

These fibers arise from pontine nuclei &

cross over to opposite side middlecerebellar peduncle.

These fibers are part of cortico-ponto-cerebellar pathway.


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SUPERIOR PEDUNCLE: AFFERENTS:

Anterior spino-

cerebellar tract.

Rubro-cerebellartract (from red

nucleus).

Tecto-cerebellar

(from tectum of

midbrain).


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EFFERENTS:

To Red nucleus, then to thalamic nucleithen to Cerebral cortex.

Other fibers go directly ventro-lateral & ventro anterior thalamic nuclei cerebral cortex

.

Some basal ganglia.


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CEREBELLUM HASRECIPROCAL CONNECTIONS 1) CEREBRAL CORTEX

2) RETICULAR FORMATION

3) VESTIBULAR NUCLEI

4) RED NUCLEUS

AFFERENTS EFFERENTS


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FUNCTIONS OFCEREBELLUM: Functionally divided into 3 parts:

1) lateral zone

2) intermediate zone

3) flocculo-nodular lobe & vermis.


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LATERAL ZONE:FUNCTION No body representation.

Also called cerebro-cerebellum (extensive

connections with cerebral cortex).

Program & plan movement. Plans sequence & timing of each component of

movement.

Smooth progress of movement, e-g, eating thecurry & bread (bread curry mouth).


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*cerebellum does not INITIATE

movement BUT COORDINATES it.

In cerebellar disease loss of smooth

progression of movements.

Extra motor predictive function.

Helps to access timing of movement.


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INTERMEDIATE ZONE: FUNCTION Also called spino-cerebellum, due toconnection with spinal cord.

Face & limbs are represented.

Coordination of movements (distal part oflimbs).

Acts as a comparator.

Compares intended plan of movement withactually performed movement.

In case of discrepancy, corrective signals aresent.


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Cerebellum gets intended plan ofmovement from motor cortex & also from

red nucleus.

Fig shows cerebral & cerebellar control of

voluntary movements involving especially

intermediate zone & its associated

nucleus interpositus.


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It recieves information actually performed

movements from PROPRIOCEPTORSthrough spino-cerebellar tracts.

Compared & corrected via signalsthrough red nucleus & thalamic nuclei to

motor cortex.


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Also controls: rate, range & direction of

movement.

Damping function.

Prevents pendular movements & tremors

(pendular knee jerk in case of disease)


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Also controls very rapid movements like

typing (ballistic movements).

Also controls very rapid eye movement

(reading & when a person in a moving

vehicle, fixate the outside scene).


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FUNCTION OF FLOCCOLONODULARLOBE & VERMIS: Controls posture & equilibrium.

Also concerned with motion sickness.

Controls stretch reflex & muscle tone.

Normal influence is facilitatory on stretch reflex& muscle tone.

From here purkinje nerve fibers vest nuclei(bypass deep nuclear cells)

Also called vestibulo-cerebellum due toconnection with vestibular nuclei.


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CEREBELLAR DISEASE: Involvement of cerebellar cortex & 1 or

more of deep cerebellar nuclei.

*No muscle paralysis & no sensory lossoccurs. (MCQ)


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FEATURES:1) ATAXIA: Incoordinate movements due to defect in

control of RANGE, DIRECTION, RATE &

TIMING of movement. Asynergia (no synergism between

agonists & antagonists; normal

synergism = when agonists contract,antagonists relax).


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2) DYSMETRIA & PASTPOINTING: Inability to control range or extent of

movement.

Dysmetria also manifest as pastpointing.

When patient tries to touch an object

hand overshoots (past pointing).


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3) ADIADOCOKINESIA /DYSDIADOCOKINESIA: Inability to perform RAPID, ALTERNATE,

OPPOSITE movement (rapid supination

& pronation of arm).


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4) DRUNKEN GATE /STAGGERING GATE: Patient walks on a broad base.

SPECIFIC POSTURE: Head is rotated &

flexed towards the side of lesion.


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5) SLURRED SPEECH: Due to dysarthria ( disordered

articulation).

Incoordination of muscles of articulation. Some words or syllables are spoken loud

& others are spoken in weak tone.

Some are held for long period & someare spoken short.


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6) INTENTION TREMORS /ACTION TREMORS: Absent at rest.

Appear when patient performs some

voluntary action. Example of drinking water from a cup.


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7) REBOUNDPHENOMENON: Patient cannot stop a movement

abruptly.

Example of flexion of elbow may hithis face.


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8) DECOMPOSITION OFMOVEMENTS: Patient is not able to perform actions

involving simultaneous movement at

more than 1 joint. Movements are broken into components.

Loss of smooth progression of 1

movement to other.


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9) NYSTAGMUS: Rhythmic rapid movement of eyeballs

when eyes are focused on 1 side.

Cerebellum has a damping function,which is disturbed.


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10) PENDULAR KNEEJERK: Due to loss of damping function of

intermediate zone of cerebellum.


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11) HYPOTONIA: Due to loss of excitatory action of

cerebellum on stretch reflex & muscle

tone.

lect 4 cerebellum improved

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