Coordination of movement and Cerebellum

Prof. Vajira Weerasinghe

Professor of Physiology

Faculty of Medicine

University of Peradeniya

(www.slideshare.net/vajira54)

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

Cerebellum

• modify movement

• receive information from the motor cortex

• send information back to cortex via the thalamus

Functional significance of cerebellum

• Coordination of voluntary movements

• Maintenance of balance and posture

• Motor learning

• Cognitive functions

Lobes

• Anterior lobe and part of posterior lobe– receives information from the spinal cord

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

• Flocculonodular lobe – involved in controlling the balance through vestibular

apparatus

Zones

• 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)

• Olivocerebellar – from inferior olive

• 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

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

‘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

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

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