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PSYC 211 - Chapter 8-1.docx

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PSYC 211
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Chapter 8 Control of MovementControl of Movement by the Brain 1Movements can be initiated by different reflexes like rapid stretch of muscle triggers monosynaptic stretch reflex stumble causes righting reflexes rapid approach of object to face causes startle2Also food causes eating 3Because no single cause of behaviour we cant find a single starting point in describing brain mechanisms that control movement4Both brain and spinal cord can control different things at the same time Organization of the Motor Cortex 5Primary motor cortexlies on precentral gyrus just rostral to central sulcus6Stimulating neurons on parts of primary motor cortex causes movements of particular parts of the body So shows somatotopic organizationtopographically organized mapping of parts of the body that are represented in a particular region of the brain7Motor homunculus Penfield disproportionate representation of parts used for speech lips fingers8Primary cortex organized by movements of parts of body each movement involves a bunch of muscles 9Complex neural circuitry represented by individual neurons in primary motor cortex and motor neurons in spinal cord that cause muscles to contract10Commands and movement intitiated are assisted and modified by basal ganglia and cerebellum11Graziano and Aflalo stimulation of area of primary motor cortex for a brief amount of time caused brief movements However prolonged stimulation caused a longer set of movements Ex stimulating of one region caused hand to approach mouth and then mouth to open and close One region caused squinting and defence by hands The map was consistent from animal to animal12Principal cortical input to primary motor cortexfrontal association cortexlocated rostral to it 132 regions immediately adjacent to primary motor cortex supplementary motor area and premotor cortex both important Receive info from parietal and temporal lobes and send efferent axons to primary motor cortex14Supplementary motor area SMAlocated on medial surface of brain just rostral to primary motor cortex15Premotor cortexlocated on lateral surface also just rostral to primary motor cortex16Primary motor cortex also receives info from primary somatosensory cortex neurons from somato that represent parto f the body send axons to corresponding neurons in primary motor cortex that move muscles in same part of body17Rosen and Asanuma somato neurons that respond to touch on back of the thumb send axons to motor neurons that cause thumb extension and soma nueonrs that respond to touch on front of thumb correspond to motor neurons that cause thumb flexion 18Conclusion rapid feedback from motor system during manipulating of objects Cortical Control of Movement The Descending Pathways 19Neurons in primary motor cortex control movements by 2 tracts20Both named for their locations in white matter in spinal cord 1Lateral group involved in control of independent limb movements especially of hands and fingers Independentleft and right limbs make different movements or one limb moves while other remains still not coordinate limb movements 1Corticospinal tract controls hand and finger movements Postural adjustments of trunk and use of limbs for reaching and locomotion are unaffected2Some monkeys have trouble releasing grasp when picking up objects but not when climbing walls so different mechanisms involved3Cortical axons that terminate in gray mater of spinal cord4Cell bodies responsible for these axons located in primary motor cortex receive a lot of input from it5Neurons in parietal and temporal lobes also send axons through this path6Axons leave cortex and travel through subcortical white matter to ventral midbrain penduncles7Leave penduncles and form lateral corticospinal tract8Most axons in lateral cortico tract originate in primary motor cortex and supplementary motor area that control distal parts of limbs lower legs feet and toes form synapses directly via interneurons with motor neurons in gray matter of spinal cord in lateral part of ventral horn These control muscles of distal limbs like arms hands and fingers 9Rest of fibers descend through ipsilateral spinal cord forming ventral corticospinal tract part of ventromedial group 10Axons of ventral cortico tract originate in upper leg and trunk regions of primary motor cortex descend to appropriate region of spinal cord and divide sending terminal buttons into both sides of the gray matter11Control motor neurons that move muscles of upper legs and trunk12Corticobulbar tract13Projects to medulla sometimes called bulb14Similar to corticospinal but terminates in 5th 7th 9th 10th 11th and 12th cranial nerves these nerves control movements of face neck and tongue and parts of extraocular eye muscles 15Rubrospinal tract16Originates in red nucleus of midbrain receives its most important inputs from motor cortex via corticorubral tract from cerebellum
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