Y2 s2 locomotion coordination 2014
Transcript of Y2 s2 locomotion coordination 2014
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Coordination of movement and Cerebellum
Prof. Vajira Weerasinghe
Professor of Physiology
Faculty of Medicine
University of Peradeniya
(www.slideshare.net/vajira54)
Y2S2 Locomotion module
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Objectives
1. Discuss the role of the cerebellum on motor coordination
2. Explain giving examples how coordination is affected in neurological disease
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Cerebellum
• modify movement
• receive information from the motor cortex
• send information back to cortex via the thalamus
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Functional significance of cerebellum
• Coordination of voluntary movements
• Maintenance of balance and posture
• Motor learning
• Cognitive functions
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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
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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
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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)
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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
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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
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Functional unit of the cerebellar cortex
• a Purkinje cell
• a deep nuclear cell
• inputs
• output from the deep nuclear cell
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Purkinje cell
Inputfrom Inferiorolive
Inputfrom otherafferents
Climbingfibre
Mossy fibre
Granule cells
Deep nuclearcell
Output
excitationexcitation
inhibition
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• 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
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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
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Overview of motor system hierarchy
1. Motor areas in the cerebral cortex
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Overview of motor system hierarchy
1. Motor areas in the cerebral cortex
2. Brainstem
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Overview of motor system hierarchy
1. Motor areas in the cerebral cortex
2. Brainstem
3. Spinal cord
motor circuits
rhythmic movements reflexes voluntary movements
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Overview of motor system hierarchy
1. Motor areas in the cerebral cortex
2. Brainstem
3. Spinal cord
motor circuits
rhythmic movements reflexes voluntary movements
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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
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‘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
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• ‘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
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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
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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
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Neurotransmitters
• Excitatory: glutamate» (Climbing, mossy, parallel fibres)
• Inhibitory: GABA» (Purkinje cell)
• Serotonin and Norepinephrine are also known to be involved
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Cerebellar disorders
• Examples – Cerebellar stroke– Hereditary spinocerebellar ataxia– Alcoholic cerebellar degeneration
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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
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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
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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
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Features of cerebellar disorders
• dysdiadochokinesis• unable to perform rapidly alternating movements
• dysarthria• slurring of speech• scanning speech
• nystagmus• oscillatory movements of the eye
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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
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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
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Cerebellar degeneration
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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
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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
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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