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  1. 1. THE MOTOR SYSTEM, part II
  2. 2. THE MOTOR SYSTEMThe brain influences activity of the spinal cord in order to generate voluntarymovementsHierarchy of controls Highest level: Strategy, the goal of the movement and best way to achieve it. Associated to neocortex and basal ganglia Middle level: Tactics, the sequence of muscle contraction to achieve the goal. Associate to motor cortex and cerebellum Lowest level: Execution, activation of motor neurons that generate the movement. Associated to brain stem and spinal cord
  3. 3. DESCENDING SPINAL TRACTSAxons from brain descend along two major pathways Lateral Pathways: involved in voluntary of distal musculature movement under cortical control Ventromedial Pathways: involved in control of posture and locomotion, under brain stem control
  4. 4. THE LATERAL PATHWAYS Base of midbrai cerebral n peducle Right red nucleus Medullary pyramid pyramidal decussationCorticospinal Rubrospinaltract tract
  5. 5. THE VENTROMEDIAL PATHWAYSVestibulospinal tract:information from vestibularsystem. Control neck andback muscles. Guide headmovements Vestibular nucleus Vestibulospinal Tectospinal tract tract Spinal cord Tectospinal tract: information from retina and visual system. Guide control eye movements.
  6. 6. THE VENTROMEDIAL PATHWAYSPontine reticulospinal tract:enhance antigravity reflexs,helps maintaining a standingposture Cerebellum pons Pontine reticular formation Medullary reticular formation Reticulospinal tract Medullary reticulospinal tract: opposite function Spinal cord
  7. 7. THE MOTOR CORTEXArea 4 = “Primary motor cortex” or “M1”Area 6 = “Higher motor area”Lateral region Premotor area (PMA), controls distal motor unitsMedial region Supplementary motor area (SMA), controls proximal motor units
  8. 8. THE MOTOR CORTEXThe Contributions of Posterior Parietal and Prefrontal CortexRepresent highest levels of motor control. Help in deciding about actions and their outcome, by integratingmany source of information APs of PMAArea 5: Inputs from areas 3, 1, and 2 neuronArea 7: Inputs from higher-order visual cortical areas.They both project to Area 6 Instruction Trigger
  9. 9. THE BASAL GANGLIABasal ganglia Project to the ventral lateral (VLo) nucleus Provides major input to area 6Cortex Projects back to basal ganglia Forms a “loop” in order to select and initiatiate willed movements
  10. 10. THE BASAL GANGLIAAnatomy of the Basal GangliaCaudate nucleus, putamen, globus pallidus, subthalamic nucleusSubstantia nigra: Connected to basal ganglia
  11. 11. THE BASAL GANGLIAThe Motor Loop: Selection and initiation of willed movementsExcitatory connection from the cortex to cells in putamenCortical activation excites putamen neurons. Inhibits globus pallidus neurons.Release cells in VLo from inhibition. Activity in VLo influences activity in SMA
  12. 12. THE BASAL GANGLIABasal Ganglia Disorders: Hypokinesia and hyperkinesiaParkinson’s diseaseSymptoms: Bradykinesia, akinesia, rigidity and tremors of hand and jawOrganic basis: Degeneration of substantia nigra inputs to striatumDopa treatment: Facilitates production of dopamine to increase SMA activityHuntington’s diseaseSymptoms: Hyperkinesia, dyskinesia, dementia, impaired cognitive disability,personality disorderHemiballismusViolent, flinging movement on one side of the bodySome examples…. PARKINSON
  13. 13. THE CEREBELLUMFunction: Sequence of muscle contractionsLesion: Ataxia, characterized by uncoordinated and inaccurate movements.Dysynergia, dysmetricAnatomy: Folia and lobules, Deep cerebellar nuclei (relay cerebellar cortical outputto brain stem structures) Vermis (contributes to ventromedial pathways) Cerebellarhemispheres (contributes to lateral pathways)
  15. 15. THE CEREBELLUMThe Motor Loop Through the Lateral CerebellumAxons from layer V pyramidal cells in the sensorimotor cortex form massive projections to ponsCorticopontocerebellar projection are 20 times larger than pyramidal tractFunction: Execution of planned, voluntary, multijoint movements