Function of Cerebellum

8/12/2019 Function of Cerebellum

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recap

• Main motor pathway

- Direct*CST

*CBT

- Indirect• Basal Ganglia

- circuit

- neurotransmitter

- cerebellum





Discussion

• Cellular organization (Neuronal Circuit)

• Input signals to cerebellum

• Output signals f rom cerebellum

• Function of cerebellum in motor control• Clinical abnormalities



CELLULAR ORGANIZATION OF

CEREBELLAR

(NEURONAL CIRCUIT)



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



CORTE AND #$ITE MATTER



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



C o r t e x

W h i t e

M a t t e r







Functional unit of cerebellar

• Input f ibres !

- Climbing f ibre

- Mossy f ibre

• Output !

- "urkinje f ibre



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




• 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



"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




• Other inhibitory cells in the cerebellum !

- Basket cells

- Stellate cells

- Golgi cells



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 !



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



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



FUNCTION OF CEREBELLUM IN

MOTOR CONTROL





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



• 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





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



') 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



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



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



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



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



CLINICAL ABNORMALITIES OF

CEREBELLUM



Clinical abnormalities of cerebellum

• Dysmetria

• Ataxia• Failure of progression

–

Dysdiadochokinesia – Dysarthria

• Intention tremor

– Cerebellar nystagmus

• $ypotonia




• 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




• 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




• 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




• $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



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…



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

Documents

Function of Cerebellum