6 - Motor Units & Muscle Action lecture slides

6 - Motor Units & Muscle Action lecture slides - Action...

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Action and Movement Motor Units and Muscle Action – The Neuromuscular System (converting nervous system activity into movement) Neurophysiology University of Colorado at Boulder Department of Integrative Physiology
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Steps to Learning Goal(s) ± Motor Units and Muscle Action Motor neuron-muscle relationship: the motor unit Regulation of the force of contraction differences in motor units activation/recruitment of motor units contractile proteins Diseases of the motor unit Aging and the motor unit
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Recommended Reading ± From Kandel et al. (2000) Principles of Neuroscience Chapter 34: The Motor Unit and Muscle Action, pp. 674-693 Chapter 35: Diseases of the Motor Unit, pp. 695- 697, 703-704
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Neural Centers Responsible for Movement (1) ± Ultimately all movements produced by skeletal muscles are initiated by motor neurons ( α / lower / somatic motor neurons) extensive dendritic trees receive ~50,000 -80,000 synaptic inputs from descending pathways , spinal interneurons & afferents (both excitatory & inhibitory) which are integrated into output signal that activates skeletal muscles with force appropriate to task final common pathway afferents ± Outcome of activating neuromuscular system is production of coordinated, controlled muscle contractions (movement).
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Motor Neuron-Muscle Relationships (2) ± A typical muscle consists of many thousands of muscle fibers working in parallel, & organized into a smaller number of motor units . motor unit = one α -motor neuron & all skeletal muscle fibers it innervates muscle unit = all muscle fibers in a motor unit motor pool = all motor neurons innervating a single muscle ± Motor unit represents connection between nervous system and muscle; it is, thus, the functional unit of the neuromuscular system. ± Activation of each muscle is controlled by a population of motor units; the number of motor units varies in different muscles.
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Motor Neuron-Muscle Relationships (3) ± Each α motor neuron only innervates fibers from one muscle (each muscle fiber is only innervated by 1 motor neuron). end-plate ± When a motor neuron fires an action potential, all muscle fibers in the motor unit twitch together. ± Somata of motor pool are clustered within ventral horn of spinal cord in a motor nucleus , which is arranged longitudinally along several spinal segments.
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(4) ± Cell bodies of α motor neurons are somatotopically organized within spinal cord. somatotopy = arrangement reflects organization of body ± Motor neurons innervating axial muscles are located medially, whereas those innervating distal muscles are located more laterally. In addition, motor neurons innervating flexors are
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6 - Motor Units & Muscle Action lecture slides - Action...

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