cerebellum 4 -5

7/30/2019 Cerebellum 4 -5

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CEREBELLUM


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Some Terminologies

White matter : myelinated fibre tracts Gray matter : areas of neuronal cell bodies

Tracts: collections of axons subserving similarfunction or location in CNS

Nerves: peripheral axons

Nucleus : collection of neurons subserving similarfunction in CNS e.g., caudate nucleus, red nuclei

Brainstem:Midbrain (Mesencephalon) + Pons +

Medulla Oblongata

Folia : Leaves

Vermis: Worm


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Table 5.3 (1)

Page 144

Hypothalamus

Brain stem

Cerebral cortex

Thalamus

(medial)

Basal nuclei

(lateral to thalamus)

Cerebellum

Spinal cord

Midbrain(Mesencephalon)

Pons

Medulla

oblongata

Brain components

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem

(midbrain, pons,

and medulla)

Diencephalon


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THE CEREBELLUM

Located dorsal to the pons and medulla

Makes up 11% of the brains mass

Cerebellar activity occurs subconsciously

Provides precise timing and appropriate

patterns of skeletal muscle contraction

Programming ballistic movementsActs as comparator for movements

Comparing intended and actual movement

Correction of ongoing movements

Internal & external feedback

Deviations from intended movement

Motor learning

Shift from conscious ---> unconscious


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Anatomy of the Cerebellum

2 symmetrical hemispheres connected medially by the Vermis

Folia: Transversely oriented gyri3 lobes in each hemisphere: Anterior, Posterior, Flocculonodular (FN)

Neural arrangement: Gray matter (Cortex), White matter (Internal),

Scattered cerebellar nuclei: dentate, globose, emboliform, fastigial

Arbor vitae (tree of life): distinctive treelike pattern of the white matter

Folium


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Cerebellum

Lateral part

Intermediate part


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CEREBELLUM:THE STRUCTUREInputs to the cerebellar cortex: Climbing fibers & Mossy fibers

Climbing fibers: originate in the inferior olive of the medulla

Mossy fibers: originate in all the cerebellar afferent tracts apart from inferior

olive

Purkinje cells: The final output of the cerebellar cortex

3 LayeredCerebellar

Cortex


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Climbing fibers: excite the Purkinje cells

Mossy fibers: excite the granule cellsGranule cells: make excitatory contact with the Purkinje cells

Purkinje cells: Tonic inhibition on the activity of the neurons of the cerebellar nuclei

=> All excitatory inputs will be converted to the inhibition

=> Removing the excitatory influence of the cerebellar inputs (erasing)

Cerebellum: 3 layered cortex


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Cerebellar Peduncles

Three paired fiber tracts connect the cerebellum to the brainstem:

Superior peduncles connect the cerebellum to the midbrain;

Middle peduncles connect the cerebellum to the pons and to the axis of

the brainstem;

Inferior peduncles connect the cerebellum to the medulla.

Cerebellar

Peduncles


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Cerebellar Peduncles

Superior peduncles (to the midbrain):

Fibers originate from neurons in the deep cerebellar nuclei &

communicates with the motor cortex via the midbrain and

the diencephalon (thalamus)

Middle peduncles (to the pons):

Cerebellum receives information advising it of voluntary motor

activities initiated by motor cortex

Inferior peduncles (to the medulla):Afferents conveying sensory information from muscle proprioceptors

throughout the body & from the vestibular nuclei of the brainstem

(Spinal cord)


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Cerebellar Input


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Inputs to cerebellum from spinocerebellar tracts have a

somatotopic organization.

2 maps of body Primary fissure

Signals from the motor cortex, which is also arranged somatotopically,

project to corresponding points in the sensory maps of the cerebellum.


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CEREBELLAR INPUTS

Vermis Receives input from spinal cord regarding somatosensory and

kinesthetic information (intrinsic knowledge of the position of the limbs) Damage leads to difficulty with postural adjustments (cerebellar ataxia)

Intermediate Zone Receives input from the red nucleus and somatosensory information

from the spinal cord

Damage results in rigidity & difficulty in moving limbs

Lateral Zone Receives input from the motor and association cortices through the pons

Projects to the dentate nucleus, which projects back to primary and

premotor cortex Damage leads to 4 types of deficits:

- Ballistic movements (cerebellar ataxia)- Coordination of multi-joint movement (lack of coordination: asynergia)

- Muscle learning (loss of muscle tone: hypotonia)

- Movement timing


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Outputs of the Cerebellum

Dentate nuclei: project contralaterally through

the superior cerebellar peduncle to

neurons in the contralateral thalamus &

from thalamus to motor cortex

Func.: influence planning and initiation of

voluntary movementEmboliform & Globose nuclei: project mainly

to the contralateral red nuclei & a small

group is projected to the motor cortex

Red Nuclei Rubrospinal Tract

control of proximal limb muscles

Fastigial nuclei: project to the vestibular nuclei

& to the pontine and medullary reticular

formationVestibulospinal & Reticulospinal tracts

Cerebellar nuclei: dentate, globose, emboliform, fastigial


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Inputs and outputs of the Cerebellum


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Clinical Findings and Localization of Cerebellar Lesions

Ataxiarefers to disordered contractions of agonist and antagonist

muscles and lack of coordination between movements atdifferent joints typically seen in patients with cerebellar lesions.

Normal movements require coordination of agonist and antagonist

muscles at different joints in order for movement to have smooth

trajectory.

In ataxia movements have irregular, waveringcourse consisting of continuous

overshooting, overcorrecting and

then overshooting

again around the intended trajectory.

Dysmetria = abnormal undershoot or overshoot during

movements toward a target

(finger-nose-finger test).


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Cerebellum and Motor Learning

Deficits in learning complex motor tasks aftercerebellar lesions

fMRI studies : cerebellum active during

learning of novel movements

Postulated that cerebellar nuclei store certain

motor memories

May be involved in cognitive functions


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Cerebellum: Control of Voluntary Movement

Information sources: lesions & damages &

experimental stimulation of cerebellar nuclei

Primary function:

1. To supplement & correlate the activities of other motor areas

2. Control of posture3. Correction of rapid movements initiated by cerebral cortex

4. Motor learning

(Frequency of nerve impulses in the climbing fibers almost doubles when a we earns a new task)

Movement Control:a. Inputs from motor cortex inform the cerebellum of an intended

movement before it is initiated

b. Sensory information is then received via the

spinocerebellar tract

c. An error signal is generated and is fed back to the cortex

Cerebellum has no direct connection to the spinal motoneurons (indirect effect).


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Cerebellar Processing

Cerebellum receives impulses of the intent to initiatevoluntary muscle contraction

Proprioceptors and visual signals inform the cerebellumof the bodys condition

Cerebellar cortex calculates the best way to perform amovement

A blueprint of coordinated movement is sent to thecerebral motor cortex

Cerebellar Cognitive Function

Plays a role in language and problem solving

Recognizes and predicts sequences of events


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GENERAL FEATURESOF CEREBELLUM :

Lateral aspect of brainstem & cerebellum ,

showing cerebellar

peduncles.

It controls equilibrium, it influences

posture & muscle tone and coordinatesthe movements

Its surface is high convoluted, forming

folds or folia, being oriented transversely

It lies behind Pons & M.O. , separatedfrom them by the cavity of 4th ventricle.

It is connected to brain stem (medulla,

pons& midbrain) by inferior, middle &

superior cerebellar peduncles respectively.

The cerebellum consists of a midline

vermis and 2-lateral hemispheres.

Anatomically , it is divided into anterior

, posterior & flocculo-nodular lobes.


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EXTERNAL FEATURESOF CEREBELLUM :It has anterior notch ,which iswider and lodging the back of pons

& medulla. It is separated fromthem by cavity of 4thventricle

It has also posterior notch

occupied by falx cerebelli, which

separates the 2 cerebellar H.

Inferior surface : rounded on

each side and presents :

a deep groove (vallecula) betweenthe 2-cerebellar hemispheres,which

is occupied by the inferior vermis.

-Tonsil is a small part of cerebellar

hemisphere that lies lateral to

inferior vermis.

Superior surface

Inferior surface

EXTERNAL FEATURES OF CEREBELLUM :


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EXTERNAL FEATURESOF CEREBELLUM :

Superior surface : lies beneathtentorium cerebelli and has a raised superior

vermis + a large cerebellar hemisphere oneach side + primary & horizontal fissures.

1- Primary fissure V-shaped,well defined

fissure, lies on superior surface and

separates the small anterior lobe from the

larger middle lobe (or posterior lobe).

2- Horizontal fissure lies along the sides of

cerebellum, extending from anterior notch

to posterior notch, separates the superior

from the inferior surfaces.

3- Secondary (posterolateral) fissure

lies on inferior surface and separates

flocculo-nodular lobe from the ramainder

of cerebellum.

F i l bdi i i f


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Schematic drawing of cerebellum

showing the relationshipsbetween the

anatomical & functional divisions of

cerebellum.

Green =archi-cerebellum,

blue=paleo-cerebellum.

Pink= neo-cerebellum

Functional subdivision of

cerebellum :1- Archi-cerebellum =

posterior lobe(Vestibular part) :

_It is formed of the flocculo-nodular lobe + associated fastigial

nuclei, lying on inf. Surface in frontof postero-lateral fissure.

_Embryologically, it is the oldest

part of cerebellum.

_It receives afferent Fs. Fromvestibular apparatus of internal ear

Via vestibulo-cerebellar tracts.

_It is concerned with equlibrium.


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Connections of

archicerebellum

I-Archicerebellum

It is concerned with equilibrium.

It represents flocculo-nodular lobe.

It has connections with vestibular &

reticular nuclei of brain stem

through the inferior cerebellar

peduncle.

Afferent vestibular Fs. Pass fromvestibular nuclei in pons & medulla to the

cortex of ipsilateral flocculo-nodular lobe.

Efferent cortical (purkinje cell) Fs.Project to fastigial nucleus, which projects to

vestibular nuclei & reticular formation.

It affects the L.M.system bilaterally via

descending vestibulo-spinal & reticulo-spinal


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Schematic drawing of cerebellum

showing the relationshipsbetween the

anatomical & functional divisions of

cerebellum.




2- Paleo-cerebellum=

(spinal part) :-_it is formed of midline vermis+ surrounding paravermis +

globose & emboliform nuclei.

_It receives afferent proprio-ceptive impulses from Ms.&

tendons Via spino-cerebellar

tracts (dorsal & ventral) mainly.

-it sends efferents to red nucleus

of midbrain.-it is concerned with muscle tone


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Connections of Paleo-cerebellum.

2-Paleo-cerebellumIt is concerned with muscle tone

& posture.Afferents spinal Fs. consist of

dorsal & ventral spino-cerebellar

tract from muscle, joint &

cutaneous receptors to enter thecortex of ipsilateral vermis & para

vermis Via inferior & superior

cerebellar peduncles .

Efferents cortical fibres pass toglobose & emboliform nuclei, then

Via sup. C. peduncle to contra-

lateral red nucleus of midbrain to

give rise descending rubro-spinal

tract.


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Schematic drawing of cerebellum showing

the relationshipsbetween the anatomical &

functional divisions of cerebellum.




3- Neo-cerebellum=

(cerebral part) :

_It is the remaining largest partof cerebellum.

_It includes the most 2-cerebellar

hemispheres + dendate nuclei.

_It receives afferent impulses

from the cerebral cortex+pons

Via cerebro-ponto- cerebellar

pathway.

-it sends efferents to V.L.nucleusof thalamus.

-it controls voluntary movements

(muscle coordination).

3 N b ll


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Connections of Neo-cerebellum.

3- Neo-cerebellum

It is concerned with muscular

coordination.

It receives afferents from cerebral cortex

involved in planning of movement- to

pontine nuclei ,cross to opposite side Via

middle Cerebellar peduncle to end in

lateral parts of cerebellum (cerebro-ponto-

cerebellar tract).

Neo-cerebellar efferents project to

dendate nucleus,which in turn projects to

contra-lateral red nucleus & ventral lateral

nucleus of thalamus ,then to motor cortexof frontal lobe, giving rise descending

cortico-spinal & cortico-bulbar pathways.Efferents of dentate nucleus form a major

part of superior C. peduncle.


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CEREBELLAR LESIONS

Are usually vascular, may be traumatic or tumour. Manifestations of unilateral cerebellar lesions :

1-ipsilateral incoordination of (U.L) arm = intention tremors : it isa terminal tremors at the end of movement as in touching noseor button the shirt.2-Or ipsilateral cerebellar ataxia affects (L.L.) leg, causingwide-based unsteady gait.

Manifestations of bilateral cerebellar lesions (caused byalcoholic intoxication, hypothyrodism, cerebellardegeneration & multiple sclerosis) :1-dysarthria : slowness & slurring of speech.2-Incoordination of both arms.= intention tremors.3-Cerebellar ataxia : intermittent jerky movements orstaggering , wide-based, unsteady gait.4-Nystagmus : is a very common feature of multiple sclerosis. Itis due to impairment coordination of eye movements /so,incoordination of eye movements occurs and eyes exhibit a to-and-fro motion.

Combination of nystagmus+ dysarthria + intension tremorsconstitutes Chacottriad, which is highly diagnostic of thedisease.


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INTERNAL STRUCTUREOFCEREBELLUM :

Sagittal section of cerebellum.

T.S.of cerebellum & brain at level

of 4th V. to showcerebellar nuclei.

It consists of an outerlayer of grey matter

(cerebellar cortex) , &

inner layer ofwhite matter

containing 4-pairs of

cerebellar nuclei :above roof of 4th V. from

medial to lateral :

1-Fastigial nucleus.

2-Globose nucleus.3-Emboliform nucleus.

4-Dendate nucleus.

(theonly one that can be

seen clearly with the nakede e .

C b ll t


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Cerebellar cortex

It is highly convoluted,

forming numerous transversely

oriented folia.

It contains nerve cells,

dendrites and synaptic

connections of cellular

neurones.

The cellular organization of

the cortex consists of 3-layers :

1-Outer molecular layer.

2-Intermediate, purkinje cell

layer.

3-Inner granular layer, which is

dominated by granule cell.

T.S of cerebellar folia showinglayers of cerebellar cortex.

Afferent & Efferent connecltions and

their relationships to principal cells of

cerebellar cortex.

C r b ll r rt


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Cerebellar cortex

Molecular layer : contains1-Cells : molecular cells (stellate cells) &

basket cells.2-Nerve Fibres :

a- dendrites of Purkinje cells

(arborisations).

B-axons of granule cells. ( bifurcate to

produce 2-parallel fibres , oriented

along long axis of folium).

C-ending of climbing fibers.

Purkinje cell layer : it is formedof one layer (unicellular) of large flask-

shaped purkinje cells. Their arborisationsare at right angles to long axis to folium.

Granular layer : it is formed ofsmall granule cells & ending of mossy

fibres.


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M There are 3-types of

Nerve Fibres in whiteMatter :1-Axons of purkinje cells :

the only axons to leave cerebellar

cortex to end in deep cerebellarnuclei specially dendate nucleus.

2-Mossy Fibres : end in the

granularlayer.

3-Climbing Fibres : end in the

molecular layer.


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Afferent Fibres to cerebellum :

Mostly end in cerebellar cortex,

excitatory to cortical neurones,

as mossy or climbing Fs. passing

through the cerebellar peduncles.

The following are Afferent fibres:

1-dorsal & ventral spino-cerebellar

tract. (passing via I.C.P & S.C.P)

2-vestibulo-cerebellar Fs. (via I.C.P)

3-olivo-cerebellar Fs. (via I.C.P)/

(extrapyramidal fibres), (end as

climbing or mossy fibres)4-ponto-cerebellar Fs. (via M.C.P).

(In M.O)

Efferent Fibres of the


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M

Efferent Fibres of the

cerebellum :

It sends the following fibres :

1-Cerebello-vestibular Fs. to

vestibular nuclei of pons & M.O.

2-Cerebello-olivary Fs. To M.O.

3-Dendato-rubro-thalamic tract To

red nucleus of midbrain & ventro-

lateral nucleus of the thalamus and

finally to motor cortex of frontal

lobe to coordinate movement via

cortico-spinal & corticobulbartracts.


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THE FOURTH VENTRICLE

It is a cavity of hindbrain.

Position : lies between pons & M.O.anteriorly and the cerebellum posteriorly.

It is a diamond-shaped space which is

lined by ependyma.

Its superior angle is continuous with

cerebral aqueduct of midbrain.

inferior angle is continuous with

centeral canal of closed M.O.

Its lateral angles extend laterally to

form a lateral recess on each side to

open into subarachnoid space.


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THE BOUNDARIESOF 4TH VENTRICLE

Superiolateral boundary :-it is formed by superior cerebellar

peduncle on each side.

Inferiolateral boundary :

-it is formed by inferior cerebellar

peduncle + gracile & cuneate

tubercles on each side.


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THE ROOFOF 4TH VENTRICLE

-it is a tent-shaped when seen

laterally, and diamond-shaped when

seen behind.

-it is formed of superior & inferior

medullary vela, which are thin sheets

of white matter /consists of :ependyma covered by pia mater.

-Sup.medullary velum connects the 2

sup.cerebellar peduncles.

-Inf.medullary velum connects the 2inf.cerebellar peduncles.

-Inferior vermis of cerebellum : lies

in the middle of roof of 4th ventricle.


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THE ROOFOF 4TH VENTRICLEThe lower part of roof is

invaginated bytela choroidea of 4thventricle.

The tela choroidea is a double

layer of pia mater which encloses the

choroid plexus of 4th ventricle.

The choroid plexus is a vascular

capillary tuft covered by ependymal

cells and secretes C.S.F. into the

lumen of 4th ventricle.


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THE OPENINGSOF 4TH VENTRICLEThe roof contains 3 aperatures

which transmit C.S.F. from ventricularlumen to subarachnoid space.

Median aperature (foramen of

Magendie) : lies in the median plane at

lower end of inferior medullary velum,and opens into subarachnoid space at

cistrna magna at cerebello-medullary

angle

2 lateral openings (foramina ofLuschka) : each one lies at the lateral end

of lateral recess to open into

subarachnoid space at cerebello-pontine

angle. choroid plexus partly protrudes out

through each lateral aperture.


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THE FLOOROF 4TH VENTRICLE

A diagram to show the floor & lateral

boundaries of 4th ventricle.

It is called rhomboid fossa.

It is diamond-shaped and is

divided into right & left halves

by the median sulcus.

It is crossed in the middle bytransvere Fs. (ponto-cerebellar

Fs.)called medullary stria,

which divide floor of 4th

ventricle into upper (pontine)

&lower (medullary) part.


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boundaries of 4th ventricle.

Upper pontine part : presents

on each side of median sulcus.1-Medial eminence : a rounded

elevation produced by the abducent

nucleus.

2-Facial colliculus : an elevationon the top of lower part of medial

eminence. It is produced by the

fibres of facial nerve which

surround abducent nucleus.

3-Superior fovea : a groove lateralto facial colliculus.

4-Vestibular area : lateral to

superior fovea. It overlies superior,

medial & lateral vestibular nuclei.


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Lower medullary part :

presents on each side of themedian sulcus. 1-Inferior fovea :

inverted V-shaped groove.

2-Hypoglossal area : medial to

inferior fovea. It overlieshypo-glossal nucleus.

3-Vagal area (triangle) : between

limbs of inferior fovea.It overlies

dorsal nucleus of vagus.

4-Vestibular area : lateral to

inferior fovea. It overlies inferior

vestibular nucleus.

cerebellum 4 -5

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