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8/12/2019 Function of Cerebellum
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recap
• Main motor pathway
- Direct*CST
*CBT
- Indirect• Basal Ganglia
- circuit
- neurotransmitter
- cerebellum
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Discussion
• Cellular organization (Neuronal Circuit)
• Input signals to cerebellum
• Output signals f rom cerebellum
• Function of cerebellum in motor control• Clinical abnormalities
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CELLULAR ORGANIZATION OF
CEREBELLAR
(NEURONAL CIRCUIT)
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CEREBELLAR CORTE
• The cerebellar cortex is divided into three layers
- The innermost layer ! the granule cell layer- The middle layer ! the "urkinje cell layer
* The "urkinje cell layer forms the border
between the granule and molecular layer
- The outer layer ! the molecular layer
* is made of the axons of granule cells and thedendrites of "urkinje cells, as well as a f ew
other cell types
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CORTE AND #$ITE MATTER
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Cortex and white matter of cerebellum
CORTEX
1Molecular layer
• "arallel f ibres
• Stellate cell
• Basket cells ( junction of M & ")
' "urkinje cell layer
• "urkinje cells
3 Granular cell layer
• Granule cell
•Golgi cell
WHITE MATTER
1 Deep cerebellar nuclei
• Dentate
• Interposed (globus and
emboliform)
• Fastigial
' Mossy f ibres
3 Climbing f ibres
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C o r t e x
W h i t e
M a t t e r
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Functional unit of cerebellar
• Input f ibres !
- Climbing f ibre
- Mossy f ibre
• Output !
- "urkinje f ibre
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The Input f ibres
• Climbing f ibre ! carry information that originate
f rom inf erior olive of medulla to cerebellum
• Mossy f ibre ! carry information f rom all other
f ibres f rom diff erent parts of the brain
- Cerebrum
- Brain stem
- Spinal cord
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Functional unit of cerebellar
• Mossy and climbing f ibers will ECITE deep
nuclear cell
•
Mossy and climbing f ibers will also synapse with purkinje cell
• "urkinje cell will IN$IBIT deep nuclear cell
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"urkinje cell
• The axons of "urkinje cells id the OUT"UT f rom cerebellarcortex
• They pass information to
- Deep cerebellar nuclei
* dentate* f astigial
* interposed
- Vestibular nuclei
• The output is entirely IN$IBITOR in nature
• The neurotransmitter is GABA
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Functional unit of cerebellar
• Other inhibitory cells in the cerebellum !
- Basket cells
- Stellate cells
- Golgi cells
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IN"UT INFORMATION TO CEREBELLUM
Afferent Tracts Transmits
Vestibulo cerebellar Vestibular impulses f rom labyrinths direct
via vestibular nuclei
Dorsal spino cerebellar "roprioceptive and exteroceptiveimpulses f rom body
Ventral spino cerebellar "roprioceptive and exteroceptive
impulses f rom body
Cuneo cerebellar "roprioceptive and exteroceptiveimpulses f rom head and neck
Tecto cerebellar Auditory and visual impulses via inf erior
and superior colliculi
"onto cerebellar Impulses f rom motor and other parts ofcerebral cortex via pontine nuclei
Olivo cerebellar "roprioceptive input f rom whole body via
relay in inf erior olive
Exteroceptive receptor !
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OUT"UT INFORMATION
• Cerebellum has deep nuclei
– Dentate – Interposed (globus and emboliform)
– Fastigial
• All input signals will go either one of the deep f rom
• From the deep nuclei, the output signals leave
cerebellum and are distributed to other parts of the
brain
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OUT"UT! #here will all the eff erent
pathways lead to
PARTS OF
CEREBELLUM
NUCLEI PROJECT TO FUNCTION
Vermis Fastigial nuclei The vestibular &
reticular nuclei
For balance and
posture
Intermediate zone Interposed nuclei The red nucleus
and the thalamus nuclei
For posture, gait
and coarse movements
Lateral zone Dentate nucleus Thalamus nuclei For skilled
moements of hands
and f ingers
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FUNCTION OF CEREBELLUM IN
MOTOR CONTROL
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Function of Cerebellum in Motor
Control• The nervous system uses the cerebellum to
coordinate motor control at 3 levels !- The vestibulocerebellum
- The spinocerebellum- The cerebrocerebellum
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• The areas !
- The vestibulocerebellum ! the f locculonodular
- The spinocerebellum ! most of the vermis and
adjacent intermediate zone
- The cerebrocerebellum ! lateral zones
Function of Cerebellum in Motor
Control
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1)The vestibulocerebellum
Calculate the rates and the directions of movements
Transmit the calculated information to brainstem vestibular and reticular nuclei to compute the next required positions
Eg vestibule-ocular ref lex
Controls the balance between agonist and antagonist muscle contraction of
the spine,hip and shoulder during RA"ID changes in body positions
Maintain equilibrium of the movements and posture
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') The spinocerebellum
• Intermediate zone, vermis
• "rovide smooth, coordinate movements of the agonistand antagonist muscles of periphery especially DISTALlimb movements
• Receive intended plan of movement f rom motor cortex(cerebrum) and red nucleus (brainstem)
• Receive actual movement result f rom the distal part ofthe body
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The spinocerebellum
• "revent overshoot movements and to damp
movements – All movements are naturally pendulum’
– "endulum movement tends to overshoot
cerebellum provides the damping system
– prevents overshoot or intentional tremors
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The spinocerebellum
• Control of ballistic movements
– Movement is pre-planned and set into motion for a specif ic distance and then to stop
– Involve rapid movement that is so f ast it is not
possible to receive information f rom either
periphery or f rom motor cortex
– Examples !
* f inger typing
* saccadic movements of the eyes
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3) The cerebrocerebellum
• The lateral zone
• Concerned with ! – "lanning of sequential movements
* Ability to progress smoothly f rom one movement to the next in orderly succession
– Timing f unction
* "rovide appropriate timing for each succeeding movement
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The cerebrocerebellum
• Extramotor predictive f unction !
– "redicting the rate of progression of auditory and visual phenomenon
– Eg a person can predict f rom the changing visual
scene how rapidly he/she is approaching an object
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CLINICAL ABNORMALITIES OF
CEREBELLUM
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Clinical abnormalities of cerebellum
• Dysmetria
• Ataxia• Failure of progression
–
Dysdiadochokinesia – Dysarthria
• Intention tremor
– Cerebellar nystagmus
• $ypotonia
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Clinical abnormalities of cerebellum
• Dysmetria ! the eff ect where the movement
overshoot their intended marks – "ast pointing ! a clinical test to manif est dysmetria
• Ataxia ! dysmetria eff ect causing incoordinate
movements
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Clinical abnormalities of cerebellum
• Failure of progression
– Dysdiadochokinesia ! due to inability to predict where
the diff erent part of the body will ne So no orderly
succession of movement Can be demonstrated by rapidly changing one hand upward and downward
– Dysarthria ! lack of coordination in larynx, mouth and
respiratory muscle and inability to predict duration
and intensity*Speech ! some syllables held loud, some weak, some held long & some short intervals
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Clinical abnormalities of cerebellum
• Intention tremor + action tremor ! result
f rom overshooting or f ailure to dampen movement when movement reach the
indented mark
– Cerebellar nystagmus ! tremor of the eyeball when
one attempt to f ixate the eye
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Clinical abnormalities of cerebellum
• $ypotonia ! dereae tone of the peripheral
muscle on the same side of the lesion due todamage to the deep cerebellar nuclei because
cerebellum does f ascilitate the motor cortex
and brainstem motor nuclei
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TEST FOR CEREBELLAR FUNCTION
• Dysergia ! improperco-ordinated f unction of a muscle group
• Dysmetria ! inability to properly gauge the distance between two points
Tested with f inger-to-nose movements
• Dysdiadochokinesia ! inability to do rapid alternating movements
• Scanning speech ! prolonged separation of syllables, often seen with
cerebellar dysf unction
• GAIT Disturbances !
– Cerebellar lesions ! central cerebellar lesion shows unsteady gait, but
conventional cerebellar signs may be normal
– "osterior columns lesions ! loss of proprioceptive results in unsteady gait
when eyes are closed, but relatively normal gait when eyes are open – Festinating gait ! "arkinsonian gait, shuff ling walk
– Romberg’s test ! patient cant maintain balance with legs tight together,
with eyes closed
– Tibubation ! body tremor when standing or walking, sign of cerebellar…
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Common Causes of Cerebellar Lesions
I Multiple Sclerosis
II Cerebellat StrokesIII Tumors
IV Degeneration
V #ernicke-Korsakoff Syndrome
VI Alcoholic Cerebellar Degeneration
VII Cerebellar $emorrhage
VIIIFredrick’s /Friedreich’s Ataxia
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