Coordination of movement and Cerebellum

Prof. Vajira Weerasinghe

Professor of Physiology

Faculty of Medicine

University of Peradeniya

Y2S2 Locomotion module

Objectives

1. Discuss the role of the cerebellum on motor coordination

2. Explain giving examples how coordination is affected in neurological disease

Role of cerebellum on motor coordination

Introduction

• the cerebellum and basal ganglia are large collections of nuclei that modify movement on a minute-to-minute basis

• these regions have marked similarities between them in the overall pattern of their connections with the cerebral cortex

- both receive information from the motor cortex

- both send information back to cortex via the thalamus

Introduction

• the cerebellum sends excitatory output to the motor cortex, while the basal ganglia sends inhibitory output

• the balance between these two systems allows for smooth, coordinated movement

- a disturbance in either system will manifest itself as a movement disorder

Functional significance of cerebellum

• Functions outside conscious awareness

• Involved in coordinating motor activities and learning new motor skills

• Particularly involved in adjusting activities to meet new conditions

• May also be involved in other types of learning and in emotional reactivity

structure

• Cerebellum is divided into 3 lobes by 2 transverse fissures– anterior lobe– posterior lobe– flocculonodular lobe

• Anterior cerebellum and part of posterior

cerebellum – receives information from the spinal cord

• Rest of the posterior cerebellum – receives information from the cortex

• Flocculonodular lobe – involved in controlling the balance through vestibular

apparatus

• lateral zone– this is concerned with overall planning of

sequence and timing

• intermediate zone– control muscles of upper and lower limbs

distally

• vermis– controls muscles of axial body, neck, hip

Inputs

• corticopontocerebellar• from motor and premotor cortex (also sensory cortex)

• these tracts supplies the contralateral cerebellar cortex

• olivocerebellar• from inferior olive

– excited by fibres from

» motor cx

» basal ganglia

» reticular formation

» spinal cord

Inputs (cont’d)

• vestibulocerebellar• to the flocculonodular lobe

• reticulocerebellar• to the vermis

• spinocerebellar tracts– dorsal spinocerebellar tracts

• from muscle spindle, prorpioceptive mechanoreceptor (feedback information)

– ventral spinocerebellar tarcts• from anterior horn cell

– excited by motor signals arriving through descending tracts (efference copy)

Outputs

• through deep cerebellar nuclei: dentate, fastigial, interpositus– 1. vermis -> fastigial nucleus -> medulla, pons– 2. intermediate zone

-> nucleus interpositus-> thalamus -> cortex

-> basal ganglia-> red nucleus

-> reticular formation– 3. lateral zone -> dentate nucleus

-> thalamus -> cortex

Neuronal circuitry of the cerebellum

• Main cortical cells in cerebellum are known as Purkinje Cells (large cells)

• There are about 30 million such cells

• These cells constitute a unit which repeats along the cerebellar cortex

• Somatotopic representation of the body is present in cerebellar cortex although it is not as clear as cerebral cortex

Topographical representationvermis

intermediatezone

Functional unit of the cerebellar cortex

• a Purkinje cell

• a deep nuclear cell

• inputs

• output from the deep nuclear cell

Purkinje cell

Inputfrom Inferiorolive

Inputfrom otherafferents

Climbingfibre

Mossy fibre

Granule cells

Deep nuclearcell

Output

excitationexcitation

inhibition

• Even at rest, Purkinje cells & deep nuclear cells discharge at 40-80 Hz

• afferents excite the deep nuclear cells

• Purkinje cells inhibit the deep nuclear cells

Functions of cerebellum

• planning of movements

• timing & sequencing of movements

• control of rapid movements such as walking and running

• calculates when does a movement should begin and stop

Overview of motor system hierarchy

1. Motor areas in the cerebral cortex

Overview of motor system hierarchy

1. Motor areas in the cerebral cortex

2. Brainstem

Overview of motor system hierarchy

1. Motor areas in the cerebral cortex

2. Brainstem

3. Spinal cord

motor circuits

rhythmic movements reflexes voluntary movements

Overview of motor system hierarchy

1. Motor areas in the cerebral cortex

2. Brainstem

3. Spinal cord

motor circuits

rhythmic movements reflexes voluntary movements

Overview of motor system hierarchy

1. Motor areas in the cerebral cortex

2. Brainstem

3. Spinal cord

motor circuits

rhythmic movements reflexes voluntary movements

Cerebellum Basal ganglia

Overview of motor system hierarchy

1. Motor areas in the cerebral cortex

2. Brainstem

3. Spinal cord

motor circuits

rhythmic movements reflexes voluntary movements

Cerebellum Basal gangliaThalamus

‘Error correction’• cerebellum receives two types of information

– intended plan of movement• direct information from the motor cortex

– what actual movements result• feedback from periphery

– these two are compared: an error is calculated

– corrective output signals goes to• motor cortex via thalamus• brain stem nuclei and then down to the anterior horn cell through extrapyramidal tracts

• ‘Prevention of overshoot’– Soon after a movement has been initiated– cerebellum send signals to stop the

movement at the intended point (otherwise overshooting occurs)

• Ballistic movements– movements are so rapid it is difficult to decide

on feedback

– a high-velocity musculoskeletal movement, such as a tennis serve or boxing punch, requiring reciprocal coordination of agonistic and antagonistic muscles

– rapid movements of the body, eg. finger movements during typing, rapid eye movements (saccadic eye movements)

– therefore the movement is preplanned

planning of movements

• mainly performed by lateral zones• sequencing & timing

– lateral zones communicate with premotor areas, sensory cortex & basal ganglia to receive the plan

– next sequential movement is planned– predicting the timings of each movement

• compared to the cerebrum, which works entirely on a contralateral basis, the cerebellum works ipsilaterally

Motor learning

• the cerebellum is also partly responsible for learning motor skills, such as riding a bicycle

- any movement “corrections” are stored as part of a motor memory in the synaptic inputs to the Purkinje cell

- research studies indicate that cerebellum is a pattern learning machine

- cellular basis for cerebellum-dependent motor learning is know to be a type of long-term depression (LTD) of the Purkinje cell synapses

Neurotransmitters

• Excitatory: glutamate» (Climbing, mossy, parallel fibres)

• Inhibitory: GABA» (Purkinje cell)

• Serotonin and Norepinephrine are also known to be involved

Cerebellar disorders

• Examples – Cerebellar stroke– Hereditary spinocerebellar ataxia– Alcoholic cerebellar degeneration

features of cerebellar disorders

• ataxia – incoordination of movements– difficulty in regulating the force, range, direction,

velocity and rhythm of movements – It is a general term and may be manifested in any

number of specific clinical signs, depending on the extent and locus of involvement

– limb movements, gait, speech, and eye movements may be affected

features of cerebellar disorders

• ataxic gait• broad based gait• leaning towards side of the lesion

• dysmetria• cannot plan movements• abnormal finger nose test

• past pointing & overshoot• cannot stop at the intended point and thus overshoot

results

features of cerebellar disorders

• decomposition of movements• movements are not smooth • decomposed into sub-movements

• intentional tremor• at rest: no tremor • when some action is performed: tremor starts

features of cerebellar disorders

• dysdiadochokinesis• unable to perform rapidly alternating movements

• dysarthria• slurring of speech• scanning speech

• nystagmus• oscillatory movements of the eye

features of cerebellar disorders

• hypotonia– reduction in tone

• particularly in pure cerebellar disease• due to lack of excitatory influence on gamma motor neurons by

cerebellum

• pendular jerks• legs keep swinging after a tap

• rebound• increased range of movement with lack of normal recoil to

original position

features of cerebellar disorders

• titubation• head tremor

• truncal ataxia • patients with disease of the vermis and flocculonodular

lobe will be unable to stand at all as they will have truncal ataxia

Cerebellar degeneration

Spino Cerebellar Ataxia (SCA)

• Hereditary

• May be autosomal dominant or recessive

• About 50 types of spinocerebellar ataxia present

• Some types can be pure cerebellar

• Ataxia results from variable degeneration of neurons in the cerebellar cortex, brain stem, spinocerebellar tracts and their afferent/efferent connections

Case history 1

Alcoholic Cerebellar Degeneration

• Estimated overall prevalence of alcohol dependence is 0.5–3% of the population in Europe or USA

• Central and peripheral nervous systems are the two principal targets

• Chronic alcohol ingestion can impair the function and morphology of many brain structures particularly cerebellum

Alcoholic Cerebellar Degeneration

• Both acute and chronic ingestion of alcohol result in cerebellar dysfunction

• Main complaint in patients presenting alcohol-induced cerebellar dysfunction is difficulty in standing and walking

Case history 2

Clinical examination of cerebellar functions

• Gait (broad-based)• Muscle power (normal) • Muscle tone (hypotonia) • Finger-nose test (abnormal)• Heel-knee-shin test (abnormal)• Rapid alternating movements (abnormal)• Speech (dysarthria)• Eye movements (nystagmus)• Reflexes (pendular)• Rebound phenomenon

• ROMBERG TEST IS NOT A SIGN OF CEREBELLAR DISEASE– It is a sign of a disturbance of proprioception, either

from neuropathy or posterior column disease– Patient does not know where their joint is in space

and so uses their eyes– In the dark or with eyes closed they have problems

• Video demonstrations

• Video demonstrations

• Video demonstrations