Slide 1The hierarchy of the motor systemDescending spinal tractsDescending spinal tractsDescending spinal tractsDescending spinal tractsDescending spinal tractsDescending spinal tractsDescending spinal tractsDescending spinal tractsCortical control of motor functionCortical control of motor functionCortical control of motor functionCortical control of motor functionCortical control of motor functionCortical control of motor functionCortical control of motor functionThe basal gangliaThe basal gangliaThe basal gangliaThe basal gangliaThe basal gangliaThe basal gangliaThe basal gangliaPrimary Motor cortexPrimary Motor cortexPrimary Motor cortexPrimary Motor cortexPrimary Motor cortexThe cerebellumThe cerebellumBrain control of movementSlide 33BRAIN CONTROL OF MOVEMENTNEUR 3000Dr. Joseph J. NormandinTHE HIERARCHY OF THE MOTOR SYSTEM•Strategy: the goal of the movement and the strategy to achieve that goal•Non-primary motor cortex and basal ganglia•Tactics: the sequence of muscle contractions in time and space to achieve the strategic goal•Primary motor cortex and cerebellum•Execution: activation of the motor neurons and interneurons that generate movements and any posture adjustments needed•Brain stem and spinal cord•(recall that the third source of input to alpha motor neurons we have not discussed are “upper motor neurons” of the hierarchical levels above)DESCENDING SPINAL TRACTS•Divided into two major groups•Lateral pathways through the lateral columns of the spinal cord•Voluntary movement of distal musculature•Under direct cortical control•Ventromedial pathways through the through the ventromedial columns of the spinal cord•Posture and locomotion•Distal and proximal muscles•Reflexively maintained•Under brainstem controlDESCENDING SPINAL TRACTS•The lateral pathways: two tracts•Corticospinal tract (pyramidal tract)•Rubrospinal tractDESCENDING SPINAL TRACTS•The lateral pathways: two tracts•Corticospinal tract (pyramidal tract)•Rubrospinal tract•Lesions of the lateral pathways in monkeys results in:•Paralysis of voluntary movement on the contralateral side•Gradual recovery•Permanent loss of voluntary movement of individual parts of the body•Could not move shoulders, arm, hand, etc. independently•Normal posture•If you lesion just the corticospinal tract, you get above•If you then lesion the rubrospinal tract, no recovery! What does that mean?DESCENDING SPINAL TRACTS•The ventromedial pathways: four tracts•Vestibulospinal tract•Tectospinal tractDESCENDING SPINAL TRACTS•The ventromedial pathways: four tracts•Vestibulospinal tract•Vestibular nucleus receives information from the vestibular system•Terminates at cervical motor neurons for the neck and back and lumbar motor neurons of legs•Maintains head balance and body balance w/ vestibular input•Tectospinal tract•Superior colliculus receives information from the retina•Terminates on motor neurons for eye and neck muscles•Orients eyes to new stimuli (part of attention system)DESCENDING SPINAL TRACTS•The ventromedial pathways: four tracts•Vestibulospinal tract•Tectospinal tract•Pontine reticulospinal tract•Medullary reticulospinal tractDESCENDING SPINAL TRACTS•The ventromedial pathways: four tracts•Pontine reticulospinal tract•Enhances antigravity reflexes of spinal cord to maintain posture•Medullary reticulospinal tract•Inhibits antigravity reflexes of spinal cord to maintain posture•Both receive input from motor cortex to regulate their functionDESCENDING SPINAL TRACTSCORTICAL CONTROL OF MOTOR FUNCTIONCORTICAL CONTROL OF MOTOR FUNCTIONCORTICAL CONTROL OF MOTOR FUNCTION•Stimulation of M1 neurons in people results in contractions of particular contralateral muscles (a tactic of movement?)•Stimulation of SMA/PMA neurons results in complex movements on either side of the body (a strategy of movement?)CORTICAL CONTROL OF MOTOR FUNCTION•Posterior parietal (PP) cortex & prefrontal cortex (PFC)•Posterior parietal cortex•Integrates somatosensory, proprioceptive, and visual information•Area 5: input from S1•Area 7: input from V5 (MT)•Necessary for understanding position of body in space•Projects to SMA/PMA•Prefrontal cortex•Planning and consequences•Projects to SMA/PMA•Together, provide necessary information to SMA/PMA on goals, consequences, and contextCORTICAL CONTROL OF MOTOR FUNCTION•SMA/PMA encodes what actions are desired (strategy)•Projects to M1 •M1 encodes how actions will be carried out (tactic)•In a PET experiment…•People were asked to perform a series of movements from memory•Active regions: S1, PP, PFC, SMA/PMA, M1•Strategy, tactic, execution•Asked to mentally rehearse movement, but not actually move•Active regions: S1, PP, PFC, SMA/PMA•M1 not active•Strategy, no tactic, no executionCORTICAL CONTROL OF MOTOR FUNCTION•Motor planning•In monkeys, SMA neurons increase firing rates just before a hand movement is made•Similar activity for either hand•Consistent with the concept of SMA containing a plan for coordinated movement•Humans with lesions to the SMA on one side cannot button a shirt•PMA neurons may contain a plan for goal-directed movements…CORTICAL CONTROL OF MOTOR FUNCTIONTHE BASAL GANGLIA•Subcortical input to the PMA/SMA is critical for motor function•The ventral lateral nucleus of the thalamus (VL) projects to the SMA•VL receives input from a network of structures called the basal ganglia•The basal ganglia receive input from multiple cortical areas•Together these connections from a loop that appears to select and initiate voluntary movementsTHE BASAL GANGLIATHE BASAL GANGLIATHE BASAL GANGLIATHE BASAL GANGLIA•The basal ganglia support functions to initiate and regulate voluntary movements•Globus pallidus neurons are spontaneously active, inhibiting SMA•Release from inhibition boosts activity of the SMA•This is the “go” signal for a voluntary motor functionTHE BASAL GANGLIA•Disorders of the basal ganglia support the hypothesis that it functions to initiate and regulate voluntary movements•Parkinson's disease•Characterized by the inability to initiate movements (among other motor and cognitive deficits)•Results from degeneration of dopaminergic substantia nigra cellsTHE BASAL GANGLIA•Disorders of the basal ganglia support the hypothesis that it functions to initiate and regulate voluntary movements•Huntington’s