Download cerebellum student copy 2010

Cerebellum
Dr Taha Sadig Ahmed ,
MBBS , PhD ( England ) .
Consultant , Clinical
Neurophysiology .
Associate Professor , Physiology
Department , College of Medicine
24 May 2017
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4th Ventricle
The cerebellum is located at the bottom of the brain , in the posterior
cranial fossa , over the occipital bone .
It is separated from the overlying cerebrum by a layer of leathery dura
mater called Tentorium Cerebelli
Anterior to it is Pons and 4th ventricle
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 It consists of  (1) two Cerebellar Hemispheres , connected by
(2) a middle part called Vermis , and a
(3) a posterior Flocculonodular Lobe .
Posterolateral
Fissure
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Flocculonodular Lobe
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Functionally , the Cerebellum is divided into 3 parts :
Neocerebellum
(Lateral parts
Spinocerebellum
of hemispheres )
(Vermis + medial parts of
hemispheres )
Hemisphere
Posterolateral Fissure
(1) Neocerebellum ( Cerebrocerebellum )
(2) Spinocerebellum ( Paleocerebellum) , &
Flocculonodular Lobe
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(3) 24
Vestibulocerebellum
( Floculonodular Lobe , Archicerebellum )
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It is connected to the brainstem on each side by 3
peduncles : Superior , Middle & Inferior
Inputs to the cerebellum
from the Cerebrum
Middle Cerebellar
Peduncle
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Inputs to the Cerebellum
from from the Pons
Inputs to the Cerebellum
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from the Medulla Oblongata
Although it weighs only 10 % as much as the
cerebral cortex , its surface area is about 75 %
of that of the cerebral cortex .
Cerebellar motor pathways are uncrossed, so
that injuries on one side will result in
symptoms & signs on the same side of the
body.
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Neocerebellum
( (Cerebrocerebellum )
Comprises the lateral parts
of cerebellar hemispheres.
It closely cooperates with
the cerebrum ( including
motor cortex ) cerebral
cortex in planning/
programming + execution of
voluntary movements.
It is involved in motor
learning of voluntary , skilful
movements .
It coordinates activity of
muscles involved in execution
of skilled movements.
These skilled movements are
mainly performed by distal
limb muscles ( namely hand
muscles ) .
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Thus the Neocerebellum helps
us to monitor ,coordinate , and
execute fine , skilled movement
( which is primarily voluntarily
initiated by the motor cortex ) .
And makes us able to perform
complex skilful movements such
as writing , drawing , playing
musical instruments , singing
etc
Spinocerebellum
( Paleocerebellum)
Consist of Vermis & Medial Parts of the Cerebellar
Hemispheres .
The vemis projects to the brainstem areas concerned with
control of axial and proximal limb muscles (which are concerned
with gross postural adjustments ) .
The Spinocerebellum receives 
(1) Proprioceptive inputs afferents
from all parts of the body +
(2) a copy of the “ Motor Plan ”from
the motor cortex
 It functions to 
(1) Regulates & maintains muscle tone
(2) Acts as a comparator
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Vestibulocerebellum
( Floculonodular Lobe)
It has connections to the vestibular nuclei ,
consequently , it is concerned with maintenance of body
balance & equilibrium
 It also controls the Vestibulocular Reflex ( VOR)
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Efferents from Cerebellar
Cortex
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Neocerebellar Cortical Efferents
 Neocerebellar cortex projects to to the Dentate Nucleus 
& from there to the Thalamus ( its Ventrolateral Nucleus ),
which , in turn , will project to the  Motor & Premotor Areas
of the Cerebral Cortex .
 in order to
(1) aid in motor planning
(2) coordinate activity of different muscle groups during
execution of voluntary , skilled movement
Spinocerebellar Cortical Efferents :
The Vermis projects to the Fastigial Nucleus  & from there to 
Brainstem Nuclei
The Hemispheric Portions of the Spinocerebellum project to  Nucleus
Interpositus ( i.e., Emboliform and Globose nuclei )
& from there to  Brainstem Nuclei
These Brainstem Nuclei receiving inputs from the spinocerebellum are
concerned with control of axial and proximal limb muscles ( in order to
adjust muscle tone & body posture ).
Vestibulocerebellar Cortical Efferents :
 Efferents from the Vestibulocerebellum pass directly to
Brainstem Nuclei
( & not through the DCN)
These vestibulocerebellar efferents function to regulate of
body balance
& equilibrium + the VOR ).
 Hence , it should be remembered that , though the DCN
provide the only outlet for the Neocerebellum and
Spinocerebellum , they are not the outlet/gateway for
Vestibulocerebellum
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Functions of Cellular
Elements of Cerebellar
Cortex
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Cerebellar Cellular Organization
 The cerebellum comprises
Cortex and Deep Cerebellar
Nuclei (DCN)
The DCN are 4 in number , &
are named :
(1) Dentate ,
(2) Fastigial .
(3) Globose ,
(4) Emboliform ,
NB : Globosus & Emboliform are
collectively called Interpositus
Nucleus .
Cerebellar Afferents :
These are Mossy Fibers & Climbing
Fibers .
 Climbing Fibers come from the
Inferior Olivary Nucleues , & they
provide indirect proprioceptive inputs
to the cerebellar cortex
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 Mossy Fibers, come from
(1) all parts of the body , +
(2) cerebral cortex .
As they ascend , they send
collaterals to the DCN , and
thereafter proceed ( pass on ) to
synapse on cerebellar cortical cells .
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Layers of the Cerebellar Cortex
The cerebellar cortex
is made of layers 
(1) External
Molecular layer ,
( 2) Middle Purkinje
Cell layer that is
only one cell thick ,
(3) Internal Granular
layer
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Cells of
the
Cerebellar
Cortex
The cerebellar cortex contains mainly 5 types of neurons : Purkinje ,
Granule , Basket , Stellate & Golgi cells .
(1) Purkinje Cells :
Are amongst the biggest neurons in the body .
Have very extensive dendritic arbors that extend throughout the Molecular
Layer .
Their axons , which are the only output from the cerebellar cortex , pass to
the
deep
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(2) Granule Cells
Their cell-bodies are situated in the Granular layer .
They receive inputs from the Mossy fibers and they innervate the
Purkinje cells .
Each sends an axon to the Molecular layer , where the axon
bifurcates to form a T .
Because the branches of this “ T ” are straight and run for long
distances , they are called Parallel Fibers .
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The other 3 types of neurons in the cerebellar cortex are inhibitory
neurons :
(3) Basket cells :
Are located in the Molecular layer
They receive inputs from Parallel fibers , and each projects to many
Purkinje cells .
Their axons form a basket around the cell-body and axon hillock of
each Purkinje cell they innervate .
They are excited by Parallel fibers of Granule cells , & their output
inhibits Purkinje cell discharge by a process of Feed-Forward
Inhibition .
(4) Stellate cells
Similar to Basket cells , these cells are excited by Parallel fibers of
Granule cells , & their output inhibits Purkinje cell discharge by a
process of Feed-Forward Inhibition .
They differ from Basket cells only in being more superficially located
in the cortex than Basket cells .
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Golgi cells are located in the Granular layer .
Their dendrites , which project into the Molecular layer
, receive inputs from the Parallel fibers .
Their cell bodies receive input via collateralsfrom the
incoming Mossy fibers and the Purkinje cells
Their axons project to the dendrites of the Granule
cells .
They are excited by
(1) Mossy fibers
(2) Purkinje cells , &
(3) Parallel fibers .
They inhibit the action of Mossy fibers on Granule
cells .
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The Main Inputs
(Afferents ) to the Cerebellar
Cortex (1)
There are 2 main inputs to the
cerebellar cortex : the Climbing
Fibers and Mossy Fibers , both of
which are excitatory .
Climbing Fibers :
The climbing fibers come solely
from the Inferior Olivary Nucleues
They provide an indirect
proprioceptive input to the
cerebellar cortex  bringing to it
proprioceptive information from all
parts of the body via relays in the
Inferior Olive (which receives
proprioceptive inputs from all over
the body parts )
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Each climbing fiber projects to
the dendrites of Purkinje cells ,
around which it entwines like a
climbing plant .
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The Main Inputs
(Afferents ) to the Cerebellar Cortex (2)
Mossy Fibers :
(1) These , unlike Climbing Fibers
( which provide an indirect
proprioceptive input ) do provide a
direct proprioceptive pathway (
input ) to the cerebellar cortex ,
from all parts of the body , and , in
addition
(2) Provide inputs from the Motor
Area ( M1) & related areas of the
Cerebral Cortex ( indirectly , via
relays in the pontine nuclei ).
They end on the dendrites of
Granule cells in complex synaptic
groupings called Glomeruli .
The Glomeruli also contain the
inhibitory endings of the Golgi
cells.
Climbing Fibers
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Mossy Fibers
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Corollary ( summary ) of effects of different cells &
afferents on Purkinje cells
(A) Excitatory
The fundamental circuits of cerebellar cortex are thus relatively simple :
(1) climbing fiber inputs exert a strong excitatory effect on single Purkinje
cells , whereas
(2) Mossy fiber inputs exert a weak excitatory effect on many Purkinje cells
via the Granule cells .
(B) Inhibitory
(1) Basket cells
Both are excited by Parallel fibers of Granule
cells , & their output inhibits Purkinje cells
(2) Stellate cells
( Feed-Forward Inhibition ) .
(3) Golgi cells 
Golgi cells are excited by
(1) Mossy fibers
(2) Purkinje cells , &
(3) Parallel fibers .
They inhibit the action of Mossy fibers on Granule cells
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Q : What are the Neurotransmitters Secreted by in
the Cerebellar Cortex Neurons ?
Purkinje cells
Basket cells
Stellate cells
Golgi cells
Secrete GABA
Granule cells  Glutamate
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Summary of Connections & Functions
Deep
Nuclei
Cortex
Inputs
Outputs
Function
Neocerebellum
Dentate
Lateral
portions of
Cerebellar
Hemisphere
Corticopontine/
pontocerebellar
SCP to VA/VL
In cooperation with
cerebral cortex 
Planning ,
orogramming and
execution of
voluntary & skilled
movements
Spinocerebellum
Interposed
; Fastigial
Vermis &
Medial
portions of
Cerebellar
hemispheres
Spinal and
brainstem paths
SCP to Red
Nucleus;
Fastigial to
RF
(1) Muscle tone
(2) Postural
adjustmen&
(3) Coordination
of different
muscle groups
activity for
smooth
performance of
movement
Vestibulocerebellum
Fastigial
Flocculo
Nodular Lobe
Vestibular
nuclei
Vestibular
nuclei; RF
Balance , equilibrium
& VOR
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Summary of Cerebellar Cortex Efferenrts
Projections of Neocerebellar Cortex :
The Neocerebellar Cortex projects ( sends its efferents ) to the
Dentate Nucleus  & from there to the Ventrolateral Nucleus of
the Thalamus .
Projections of Spinocerebellar Cortex :
The medial part of the Spinocerebellum ( Vermis ) projects to
the Fastigial Nuclei  & from there to the brainstem .
The hemispheric portions of the Spinocerebellum ( i.e., medial
parts of the cerebellar hemispheres ) project to the Emboliform
and Globose nuclei  & from there to the brainstem nuclei .
Projections of the Vestibulocerebellar Cortex :
Most of the Vestibulocerebellum cortex outputs ( efferents )
pass directly to the brainstem ( to regulate balance , equilibrium
& the VOR ).
However , unlike it , the rest of the cerebellar cortex ( i.e., that
of the Neocerebellum and Spinocerebellum ) sends fibers first
to the deep cerebellar nuclei , and then , these in turn will
project ( send their efferents ) to the brainstem .
Consequently
, the Deep Cerebellar Nuclei provide the only26
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Summary
The cerebellum influences movement on the ipsilateral side
of the body.
Neocerebellum is involved , in conjunction & close
cooperation with the cerebral cortex , in programming ,
planning & execution of voluntary movement ; especially
skilled movements ( which is mostly performed by the distal
limb muscles ( e.g., hand )
Spinocerebellum is primarily involved with (1) regulation &
maintenance of muscle tone , (2) gross postural
adjustments , & (3) coordination between different muscle groups for
smoothening of movement ( it acts as a comparator )
(The vermis helps coordinate movements of the axial and
proximal limb muscles ) .
Floculonodular lobe is mainly concerned with balance
equilibrium as well as VOR .
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Contd Summary ……..
Climbing fibers originate in the inferior olivary
nuclei and synapse directly onto Purkinje cells.
All other sources of input to the cerebellum enter
as mossy fibers.
Purkinje cells are the main output neurons of the
cerebellar cortex & project to the deep nuclei of
the cerebellum.
They are inhibitory to the DCN .
The deep cerebellar nuclei ( DCN ) project out
to brainstem and thalamic targets via the
superior cerebellar peduncles. They are
excitatory , but in turn , are themselves inhibited
( switched off ) by Purkinje cells .
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Cerebellar
Syndromes
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Signs of Cerebellar Disorders
Deficit
Manifestation
Ataxia
Reeling, wide-based gait
Decomposition of
movement
Inability to correctly sequence fine, coordinated acts
Dysarthria
Inability to articulate words correctly, with slurring and
inappropriate phrasing
Dysdiadochokinesia
Inability to perform rapid alternating movements
Dysmetria
Inability to control range of movement
Hypotonia
Decreased muscle tone
Nystagmus
Involuntary, rapid oscillation of the eyeballs in a horizontal,
vertical, or rotary direction, with the fast component maximal
toward the side of the cerebellar lesion
Scanning speech
Slow enunciation with a tendency to hesitate at the beginning
of a word or syllable
Tremor
Rhythmic, alternating, oscillatory movement of a limb as it
approaches a target (intention tremor) or of proximal
musculature when fixed posture or weight bearing is attempted
(postural tremor)
The Difference Between Lesions of the
Cerebellar Cortex & Lesions of DCN
If only the cortex of the cerebellum is involved ,
the movement abnormalities gradually disappear
as “ compensation ” occurs .
However , lesions of the DCN produce more
generalized defects , and abnormalities are
permanent .
For this reason , care should be taken to avoid
damaging the DCN when surgery is undertaken
to remove a tumor involving part of the
cerebellar cortex .
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Cerebellar Hemispheric
Lesions
Cerebellar lesions cause no paralysis or sensory
deficit .
When not moving , there are no externally
obvious signs .
However , upon physical examination , signs
such as hypotonia and pendular reflexes can be
elicited .
Once the patients attempts movement , ataxia
appears .
What is ataxia ? Ataxia is incoordination of due to
errors in the rate , range , force and direction of
movement .
Wth circumscribed lesions , the ataxia may be
confined/localized to only one part of the body . 32
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A/ Hemispheric Lesions
I/Ataxia (lack of coordination of muscle
movement ) , which is manifested by 
(1) Wide-based , unsteady “ drunken , or
staggering “ gait .
(2) Scanning speech
(3) Dysmetria ( also called Past-Pointing ) :
attempting to touch an object with a finger
results in overstretching to one side or the
other this promptly initiates a gross correction
action ( corrective action ) , but the correction
overshoots to the other side  Consequently ,
the finger oscillates back and forth .
This oscillation is the (4) “ Intention Tremor ” ,
which is characteristic of cerebellar disease .
This cerebellar tremor , unlike that of
Parkinson’s
disease , is absent at rest .
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Hemispheric Lesions ( Contd )
II/ Inability to “ put on the brakes ”  i.e., inability to stop
movement promptly . Normally , for example , flexion of
the forearm against resistance is quickly checked when
the resistance force is suddenly broken off . The patient
with cerebellar disease can not break the movement of
the limb , and the forearm flies back in a wide arc . This
abnormal response is known as the “ Rebound
Phenomenon ”.
III/ Adiadochkinesia ( Dysdiadochkinesia ) : Inability to
perform rapidly alternating opposite movements such as
repeated pronation and supination of the hands .
IV/ Difficulty in performing actions that involve
simultaneous motions at more than one joint . The
patient dissects such movements and carries them out
one joint at a time , a phenomenon known as “
Decomposition of Movement ” .
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B/ Flocculonodular Lobe Lesions
Midline cerebellar tumors in children , arising
from the “ Nodule ” , early in their course
(& before affecting the rest of the cerebellum) ,
damage first the Flocculonodular lobe .
Such a child is afraid ( & reluctant ) to stand
erect and move without support .
This is because if he tries to walk , he does so in
a staggering fashion on a broad base , & tends
to fall .
Moreover , selective Flocculonodular lobe
lesions may cause vertigo
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Role of the Cerebellum in Learning (1)
The cerebellum is concerned with learned adjustments that make
coordination easier when a given task is performed over & over
As a motor task is learned , activity in the brain shifts from the
Prefrontal ( cerebral ) Cortex to the (1) Parietal Cortex , (2) M1 , &
(3) Cerebellum .
The basis of learning in the cerebellum is the input via the Olivary
Nucleus.
It is worth noting , in this regard , that each Purkinje cell receives
inputs from 250,000 to 1,000,000 Mossy fibers.
By contrast , each Purkinje cell receives only a single ( only one )
Climbing fiber from the inferior olive , and this fiber makes 200-3000
synapses on the Purkinje cell .
Climbing fiber activation produces a large complex spike in the
Purkinje cell This spike produces lomg-term modification of the
pattern of Mossy fiber input to that particular Purkinje cell.
Climbing fiber activity is increased when a new movement is being
learned , and lesions of the Olivary Nucleus abolish the ability to
produce long-term adjustments in motor responses . .
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Finished
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