Motor system3 cerebellum
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Motor system3 cerebellum

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Motor system3 cerebellum Motor system3 cerebellum Presentation Transcript

  • cerebellum
    • centre of motor coordination
    • cerebellar disorders cause
      • incoordination or ataxia
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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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  • structure
      • anterior lobe (paleocerebellum)
      • large posterior lobe (neocerebellum)
      • flocculonodular lobe (archicerebellum is the oldest 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
    • Functionally cerebellum is divided into 3 areas medial to lateral
      • lateral zone
      • intermediate zone
      • vermis
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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
  • 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
  • Outputs
    • Functions
      • 1. vermis -> fastigial nucleus -> medulla, pons
      • control balance and equilibrium with the vestibular pathways
  • Outputs
    • Functions
      • 2. intermediate zone -> nucleus interpositus -> thalamus -> cortex -> basal ganglia -> red nucleus -> reticular formation
      • coordinate reciprocal contractions of agonist & antagonist muscles in limbs
  • Outputs
    • Functions
      • 3. lateral zone -> dentate nucleus -> thalamus -> cortex
      • coordinate sequential motor activities initiated by the cerebral 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.
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    • Somatotopic representation of the body is present in cerebellar cortex although it is not as clear as cerebral cortex.
  • Topographical representation vermis intermediate zone
  • Functional unit of the cerebellar cortex
    • a Purkinje cell
    • a deep nuclear cell
    • inputs
    • output from the deep nuclear cell
  • Purkinje cell Input from Inferior olive Input from other afferents Climbing fibre Mossy fibre Granule cells Deep nuclear cell Output excitation excitation inhibition
  • Output Inputs Inputs
    • Purkinje cells & deep nuclear cells fire continuously
    • afferents excite the deep nuclear cells
    • Purkinje cells inhibit the deep nuclear cells
  • 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
  • Motor Cortex Thalamus Cerebellum Muscles brain stem nuclei proprioceptive tactile feedback
    • ‘ 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
      • rapid movements of the body, eg. finger movements during typing, rapid eye movements (saccadic eye movements)
      • movements are so rapid it is difficult to decide on feedback
      • 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
  • features of cerebellar disorders
    • ataxia
      • incoordination of movements
      • ataxic gait
        • broad based gait
        • leaning towards side of the lesion
    • dysmetria
      • cannot plan movements
    • past pointing & overshoot
    • decomposition of movements
    • intentional tremor
  • features of cerebellar disorders
    • dysdiadochokinesis
      • unable to perform rapidly alternating movements
    • dysarthria
      • slurring of speech
    • nystagmus
      • oscillatory movements of the eye
  • features of cerebellar disorders
    • hypotonia
      • reduction in tone
        • due to excitatory influence on gamma motor neurons by cerebellum (through vestibulospinal tracts)
    • decreased reflexes
    • head tremor
    • head tilt