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Neuroscience (289)
NROC64H3 (81)
Chapter 14

chapter 14

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Matthias Niemeier

INTRODUCTION The central motor system is arranged as a hierarchy of control levels with the forebrain at the top and the spinal cord at the bottom see Table 141 y The highest level concerned with strategythe goal of the movement and the movement strategy that best achieves that goal y The middle level is concerned with tacticsthe sequences of muscle contractions arranged in space and time required to smoothly and accurately achieve the strategic goal y The lowest level is concerned with executionactivation of the motor neuron and interneuron pools that generate the goaldirected movement and make any necessary adjustments of postureThe proper functioning of each level of the motor control hierarchy relies so heavily on sensory information that the motor system of the brain might be considered a sensorimotor system y At the highest level sensory information generates a mental image of the body and its relationship to the environment y At the middle level tactical decisions are based on the memory of sensory information from past movements y At the lowest level sensory feedback is used to maintain posture muscle length and tension before and after each voluntary movementDESCENDING SPINAL TRACTS How does the brain communicate with the motor neurons of the spinal cord Axons from the brain descend through the spinal cord along two major groups of pathways see Fig 142 y One is the lateral column of the spinal cord o The lateral pathways are involved in voluntary movement of the distal musculature and are under direct cortical control y The other is the ventromedial column o The ventromedial pathways are involved in the control of posture and locomotion and are under brain stem controlThe Lateral Pathways The most important component of this pathway is the corticospinal tract see Fig 143a Originating in the neocortex it is the longest and one of the CNS tracts y Twothirds of the axons in the tract originate in areas 4 and 6 and is called the motor cortex y The remaining axons derive from the somatosensory areas of the parietal lobe to regulate the flow of somatosensory information to the brain A much smaller component of the lateral pathways is the rubrospinal tract which orginates in the red nucleus of the midbrain see Fig 143b A major source of input to the red nucleus is the region of the front cortex that contributes to the corticospinal tract y It contributes to motor control in many mammalian species
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