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Canada (162,168)
Neuroscience (289)
NROC90H3 (3)
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Chapter 14

Chapter 14- Brain Control.doc

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It useful to think of this motor control hierarchy as having three levelsThe highest level represented by the association areas of neocortex and basal ganglia of the forebrain is concerned with strategy oThe goal of the movement and the movement strategy that best achieves the goalThe Middle level represented by the motor cortex and cerebellum is concerned with tacticsoThe sequences of muscle contractions arranged in space and time required to smoothly and accurately achieve the strategic goal The lowest level represented by the brain stem and spinal cord is concerned with executionoActivation of the motor neuron and interneuron pools that generate the goaldirected movement and make any necessary adjustments of posture The proper functioning of each level of the motor control hierarchy relies so heavily on sensory information that the motor system of the brain might properly be considered a sensorimotor system oAt the highest level sensory information generates a mental image of the body and its relationship to the environment oAt the middle level tactical decisions are based on the memory of sensory information from past movements oAt the lowest level sensory feedback is used to maintain posture muscle length and tension before and after each voluntary movement Descending Spinal TractsAxons from the brain descend through the spinal cord along two major groupsLateral column of the spinal cordoRemember lateral pathways are involved in voluntary movement of the distal musculature and are under direct cortical controlVentromedial columnoThe Ventromedial pathways are involved in the control of posture and locomotion and are under brain stem controlThe Lateral PathwaysThe most important component of the lateral pathways is the corticospinal tractOriginating in the neocortex it is the longest and one of the largest CNS tracts23 of the axons in the tract originate in areas 4 and 6 of the frontal lobe connectively called motor cortex Most of the remaining axons in the corticospinal tract derive from the somatosensory areas of the parietal lobe and serve to regulate the flow of somatosensory information to the brain Axons from the cortex pass through the internal capsule bridging the telencephalon and thalamus course through the base of the cerebral peduncle a large collection of axons in the midbrain then pass through the pons and collect to form a tract at the base of the medullaThe tract forms a bulge called the medullary pyramid running down the ventral surface of the medulla At the junction of the medulla and spinal cord the pyramidal tract crosses or decussates at the pyramidal decussation
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