The Motor System: How the Brain Controls Movement
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The motor system is hierarchically organized, with the highest level involving strategy in the neocortex and basal ganglia, the middle level involving tactics in the motor cortex and cerebellum, and the lowest level involving execution in the brainstem and spinal cord. Descending pathways in the lateral and ventromedial regions of the spinal cord control voluntary distal movements and posture/locomotion respectively. Key structures involved in motor control include the motor cortex, basal ganglia, and cerebellum.
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The Motor System: How the Brain Controls Movement
- 1. THE MOTOR SYSTEM, part II
- 2. THE MOTOR SYSTEM The brain influences activity of the spinal cord in order to generate voluntary movements Hierarchy 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. DESCENDING SPINAL TRACTS Axons 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. THE LATERAL PATHWAYS Base of midbrai cerebral n peducle Right red nucleus Medullary pyramid pyramidal decussation Corticospinal Rubrospinal tract tract
- 5. THE VENTROMEDIAL PATHWAYS Vestibulospinal tract: information from vestibular system. Control neck and back muscles. Guide head movements Vestibular nucleus Vestibulospinal Tectospinal tract tract Spinal cord Tectospinal tract: information from retina and visual system. Guide control eye movements.
- 6. THE VENTROMEDIAL PATHWAYS Pontine reticulospinal tract: enhance antigravity reflexs, helps maintaining a standing posture Cerebellum pons Pontine reticular formation Medullary reticular formation Reticulospinal tract Medullary reticulospinal tract: opposite function Spinal cord
- 7. THE MOTOR CORTEX Area 4 = “Primary motor cortex” or “M1” Area 6 = “Higher motor area” Lateral region Premotor area (PMA), controls distal motor units Medial region Supplementary motor area (SMA), controls proximal motor units
- 8. THE MOTOR CORTEX The Contributions of Posterior Parietal and Prefrontal Cortex Represent highest levels of motor control. Help in deciding about actions and their outcome, by integrating many source of information APs of PMA Area 5: Inputs from areas 3, 1, and 2 neuron Area 7: Inputs from higher-order visual cortical areas. They both project to Area 6 Instruction Trigger
- 9. THE BASAL GANGLIA Basal ganglia Project to the ventral lateral (VLo) nucleus Provides major input to area 6 Cortex Projects back to basal ganglia Forms a “loop” in order to select and initiatiate willed movements
- 10. THE BASAL GANGLIA Anatomy of the Basal Ganglia Caudate nucleus, putamen, globus pallidus, subthalamic nucleus Substantia nigra: Connected to basal ganglia
- 11. THE BASAL GANGLIA The Motor Loop: Selection and initiation of willed movements Excitatory connection from the cortex to cells in putamen Cortical activation excites putamen neurons. Inhibits globus pallidus neurons. Release cells in VLo from inhibition. Activity in VLo influences activity in SMA
- 12. THE BASAL GANGLIA Basal Ganglia Disorders: Hypokinesia and hyperkinesia Parkinson’s disease Symptoms: Bradykinesia, akinesia, rigidity and tremors of hand and jaw Organic basis: Degeneration of substantia nigra inputs to striatum Dopa treatment: Facilitates production of dopamine to increase SMA activity Huntington’s disease Symptoms: Hyperkinesia, dyskinesia, dementia, impaired cognitive disability, personality disorder Hemiballismus Violent, flinging movement on one side of the body Some examples…. http://www.youtube.com/watch?v=ECkPVTZlfP8&feature=related PARKINSON
- 13. THE CEREBELLUM Function: Sequence of muscle contractions Lesion: Ataxia, characterized by uncoordinated and inaccurate movements. Dysynergia, dysmetric Anatomy: Folia and lobules, Deep cerebellar nuclei (relay cerebellar cortical output to brain stem structures) Vermis (contributes to ventromedial pathways) Cerebellar hemispheres (contributes to lateral pathways)
- 14. THE CEREBELLUM
- 15. THE CEREBELLUM The Motor Loop Through the Lateral Cerebellum Axons from layer V pyramidal cells in the sensorimotor cortex form massive projections to pons Corticopontocerebellar projection are 20 times larger than pyramidal tract Function: Execution of planned, voluntary, multijoint movements