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Chapter 14

Chapter 14

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Matthias Niemeier

Chapter 14: Brain Control of Movements Introduction o Hierarchy of control levels  Strategy: association areas of neocortex, basal ganglia  Tactics: motor cortex, cerebellum  Execution: brain stem, spinal cord o Ballistic movement: too fast to be altered once initiated; however uses sensory information before the movement and during for subsequent movements o Antigravity postural reflexes: can be altered once initiated o Sensorimotor system: motor relies heavily on sensory  Sensory info generates mental image of body and its relationship to the environment  Tactical decisions based on memory of sensory info from past movements  Sensory feedback used to maintain posture, muscle length, and tension Descending Spinal Tracts o Lateral pathways: involved in voluntary movement of the distal musculature and are under direct cortical control o Ventromedial pathways: involved in the control of posture and locomotion and are under brain stem control Lateral Pathway o Corticospinal tract: from neocortex 2/3 from motor cortex 1/3 more somatosensory areas; longest and one of the largest CNS tracts  Passes through the internal capsule, base of cerebral peduncle, pons, to tract at base of medulla , medullary pyramid, pyramidal tract, crosses at pyramidal decussation, lateral column of spinal cord and form lateral corticospinal tract-> dorsolateral region of ventral horns and intermediate gray matter (distal muscles) o Rubrospinal tract: red nucleus (midbrain), decussate in pons, join corticospinal tract in lateral column of spinal cord  Function of this tract has been taken over by corticospinal tract in humans o The Effect of Lateral Pathway Lesions  Can not move distal limbs independently  Slower and less accurate voluntary movements  Still can stand and maintain posture  Corticospinal tract only: movement deficit that can reappear after several months (corticorubrospinal pathway can compensate) The Ventromedial Pathway o The Vestibulospinal Tracts  Keep head balanced on shoulders as body moves  Vestibular nuclei (medulla) -> bilaterally to cervical spinal unit that control neck and back muscles  Also goes ipsilaterally down to lumbar spinal cord to keep upright balanced posture using extensor motor neurons of the legs o The Tectospinal Tract  Superior colliculus (creates map of world) -> directs head and eyes to orient to stimuli o The Pontine and Medullary Reticulospinal Tracts  Reticular formation (brain stem)  Pontine Reticulospinal tract (medial): antigravity reflexes of spinal cord through extensors of lower limbs  Medullary reticulospinal tract: liberates antigravity muscles from reflex control  Balance of two controlled by cortex The Planning of Movement by the Cerebral Cortex Motor Cortex o Area 4 (precentral gyrus)  Primary motor cortex/M1: o William Penfield: discovered this was motor cortex o Area 6: evokes complex movements  Premotor area (lateral): reticulospinal neurons for proximal motor units  Supplementary motor area (medial): innervate distal motor units directly The Contributions of Posterior Parietal and Prefrontal Cortex o Posterior parietal cortex: somatosensory, proprioceptive and visual inputs that generate a mental body image  Area 5: gets inputs from primary somatosensory cortical areas (3, 1, 2)  Area 7: gets input from higher order visual areas o Pre frontal areas: for abstract thought, decision making, anticipating the consequences of action o Both converge on area 6: where the what decisions are converted to how signals o Per Roland: used PET and discovered areas active while planning movement: somatosensory and posterior parietal areas, prefrontal cortex, area 6 and area 4  When rehearsing movement without actually doing it area 4 is not active Neural Correlates of Motor Planning o Edward Evarts: recorded activity of neurons in motor areas of awake animals o SMA decreases firing just before activity  Happens with movement of either hand so both sides are linked  If one side is damaged movement deficits are most in the coordinated actions of both hands o Apraxia: selective inability to perform complex but not simple motor acts o Ready Set Go  Ready: activity in the parietal and frontal lobes and brain centers for attention and alertness  Set: supplementary and premotor areas  Go: primary motor cortex o Weinrich and Wise: monitored discharge of PMA as monkey performed task; fires during instruction stops when movement is initiated The Basal Ganglia o Circuit: cortex (frontal, prefrontal, parietal) -> basal ganglia -> thalamus (ventral lateral VL nucleus) -> cortex (supplementary motor area) o Function: selection a
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