GSU NEUR 3000 - NEUR 3000 - Chapter 14 (33 pages)

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NEUR 3000 - Chapter 14



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NEUR 3000 - Chapter 14

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Pages:
33
School:
Georgia State University
Course:
Neur 3000 - Hon Principles of Neuroscience
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BRAIN CONTROL OF MOVEMENT NEUR 3000 Dr Joseph J Normandin THE 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 control DESCENDING SPINAL TRACTS The lateral pathways two tracts Corticospinal tract pyramidal tract Rubrospinal tract DESCENDING 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 DESCENDING SPINAL TRACTS The ventromedial pathways four tracts Vestibulospinal tract Tectospinal tract DESCENDING 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 tract DESCENDING 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 function DESCENDING SPINAL TRACTS CORTICAL CONTROL OF MOTOR FUNCTION CORTICAL CONTROL OF MOTOR FUNCTION CORTICAL 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 CORTICAL 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 CORTICAL 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 FUNCTION THE 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 movements THE BASAL GANGLIA THE BASAL GANGLIA THE BASAL GANGLIA THE 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 function THE 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 cells THE BASAL GANGLIA Disorders of the basal ganglia support the hypothesis that it functions to initiate and regulate voluntary movements Huntington s disease Characterized by the spontaneous uncontrollable movements among other motor and cognitive deficits Results from degeneration of basal ganglia including pallidum PRIMARY MOTOR CORTEX We ve discussed That prefrontal and posterior parietal cortex provides necessary information for motor planning by the SMA PMA Strategy That the go signal for the strategy output from the SMA comes from the basal ganglia But how and where is that strategy turned into a tactic of individual muscle movements PRIMARY MOTOR CORTEX M1 receives robust input from SMA PMA Also receives input from the cerebellum via the VL M1 has dense strong projections to lower motor neurons and spinal interneurons Stimulation of M1 neurons in people results in contractions of particular contralateral muscles a tactic of movement M1 neuron activity precedes is and concomitant with voluntary movement M1 neurons have preferences for direction Broadly tuned population code for a particular direction PRIMARY MOTOR CORTEX PRIMARY MOTOR CORTEX PRIMARY MOTOR CORTEX A consequence of the population coding of voluntary movement in M1 is that the more cells involved the finer grade the movement can be Recall that the parts of our body we have the most control over


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