cerebellum 4 -5
TRANSCRIPT
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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.
Green =archi-cerebellum,
blue=paleo-cerebellum.
Pink= neo-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.
Green =archi-cerebellum,
blue=paleo-cerebellum.
Pink= neo-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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THE FLOOROF 4TH VENTRICLE
A diagram to show the floor & lateral
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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THE FLOOROF 4TH VENTRICLE
A diagram to show the floor & lateral
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.