KIN 461 Week 2 Notes
KIN 461 Week 2 Notes KIN 461-401
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This page Class Notes was uploaded by Tanski Notetaker on Saturday January 30, 2016. The Class Notes belongs to KIN 461-401 at University of Wisconsin - Milwaukee taught by Dr. Peterson in Spring 2016. Since its upload, it has received 19 views. For similar materials see Principles of Motor Learning in Kinesiology at University of Wisconsin - Milwaukee.
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Date Created: 01/30/16
Week 2 Notes 1 Introduction to Movement cont I Motor systems organized into 2 control levels 0 Spinal cord 0 Brain stem 0 Motor areas of the cerebral cortex I Organized both hierarchically and parallel O Hierarchal organization permits lower levels to generate re exes I higher centers can give general commands without needing to specify all details of motor action 0 Parallel organization allows higher centers to adjust operation of spinal circuits I Descending systems can control certain functions independently I Allows brain to control pathways that produce discrete types of movement I Spinal cord is lowest level of hierarchy 0 Contains neural circuits that mediate variety of automatic and stereotyped motor patterns and re exes 0 Final common pathway control signals ultimately converge on motor neurons that innervate skeletal muscle I Final path to muscles I Sir Charles Sherrington I Brain Stem is next level 0 Has its own motor neurons 0 Axons project to and regulate networks of spinal cord intemeurons and motor neurons necessary for behavioral acts 0 Important for controlling posture and balance I Cerebral cortex is highest level 0 Consists of 3 areas I Sensory cortex I Primary motor cortex I Secondary motor area where planning of movement takes place 0 Corticospinal tract even control neurons in the limbs 0 Right hand is controlled by left side of cerebral cortex 0 Different areas control different parts of the body somatotopically organized I Spinal cord contains the cell bodies of motor neurons 0 Located in ventral horns 0 Motor neuron pools clusters of individual motor neurons that innervate individual muscles 0 Proximaldistal rule motor neurons innervating the most proximal muscles are located most medially 0 Flexorextensor rule motor neurons innervating extensor muscles lie ventral to those innervating exor muscles Week 2 Notes Muscles and Muscle Receptors I Controlled contraction of muscles allows us to 0 Move our limbs 0 Maintain posture 0 Perform tasks with great precision 0 Force produced in contraction results in change of length of muscle 0 Dependent on 3 factors I The initial length I Velocity of length change I External loads acting to oppose movement 0 Proprioceptive information information about length of muscles and the forces they generate O Monitored by 2 types of receptors I Muscle spindles I Golgi tendon organs 0 Information from these sensory receptors reaches all levels of nervous system I Cerebral cortex uses it for perception of limb position and controlling voluntary movement I Lower levels use it to control re exes Motor Unit I Consists of a single motor neuron and the muscle fibers it innervates 0 All or non response all fibers innervated contract in response to an action potential in the neuron 0 Motor unit is the smallest functional unit within motor systems 0 Innervation ratio of muscle fibers innervated by one motor neuron O Varies among muscles 0 About proportion to size of muscle 0 Small innervation ratiofiner grading of the muscle s total force by the nervous system 0 In hand muscles ratio is 100 O In larger gastrocnemius ratio is 2000 I Nervous system grades force of muscle contraction by 0 Recruitment vary of motor units activated I Increase of motor units activated increase in force whole muscle will produce 0 Rate modulation vary rate of action potentials in a motor neuron I Forcefrequency relationship increase firing rate in neuron increase in force motor unit will produce I Allows forces of successive twitches to summate I Forces produced by each twitch add until a plateau of force tetanus is reached Week 2 Notes I Unfused tetanus individual twitches can be detected 0 Produces ripple in contractile force of isolated muscle 0 Fused tetanus individual twitches can no longer be detected 0 Rate of AP increases and force produced by muscle increases to steady max value I 3 types of motor units 0 Fast fatigable I Muscle fibers contract and relax rapidly I Fatigue rapidly when stimulated repeatedly I Generate greatest force during a twitch or tetanic contraction I Motor neurons have largest cell bodies out of the three types 0 Slow fatigueresistant I Fibers have much longer contraction time I High resistance to fatigue I Generate only 110 of force of fastfatigable I Motor neurons have smallest cell bodies out of the three 0 Fast fatigueresistant I Contraction time slightly slower than fast fatigable I Almost as resistant to fatigue as slow fatigueresistant fibers I Able to produce twice as much force as slow fatigueresistant 0 Size principle when motor neuron pool is activated synaptically the initial weak inputs activate the cells with the lowest threshold for synaptic activation those with smallest cell bodies 0 As synaptic input increases in strength motor neurons with larger cell bodies are recruited according to size or strength 0 Has 2 important functional advantages I Simplifies task of regulating muscle force I Slow motor units most heavily used 0 Energy efficient Sensory Receptors 0 Muscle spindles O Sensitive to stretch O Innervated by 2 types of myelinated afferent fibers I Group Ia large diameter I Group 11 small diameter 0 Intrafusal muscle fibers of the spindle I Smaller than skeletal extrafusal muscle fibers I Don t contribute significant force to muscle contraction I Changes in their lengths sensed by the sensory terminals in the intrafusal fibers Week 2 Notes
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