y2 s2 locomotion seminar coordination 2011
TRANSCRIPT
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Staff Seminaron
Coordination of movement
Prof. Vajira Weerasinghe
Dept of Physiology
Prof. Nimal Senanayake
Dept of Medicine
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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Role of cerebellum on motor coordination
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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
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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
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structure
• Cerebellum is divided into 3 lobes by 2 transverse fissures– anterior lobe– posterior lobe– flocculonodular lobe
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• 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
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• 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)• these tracts supplies the contralateral cerebellar cortex
• olivocerebellar• from inferior olive
– excited by fibres from» motor cx» basal ganglia» reticular formation» spinal cord
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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)
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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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• Somatotopic representation of the body is present in cerebellar cortex although it is not as clear as cerebral cortex.
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Topographical representationvermis
intermediatezone
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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
• GABA is involved as the neurotransmitter
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Functions of cerebellum
• planning of movements
• timing & sequencing of movements
• particularly during rapid movments such as during walking, running
• from the peripheral feedback & motor cortical impulses, cerebellum 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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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
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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