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Lecture 22 - The Motor Unit

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Michelle French

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L22 Nov 04 11Twitchcontraction Motor Unitproduced by a single Defn a motoneuronall of muscle fibers it act potinnervatesMuscle fibers of a motor unit all contract together Motoneuronmuscle fiberParallel btwn motoneuron diameterfibres innervatedSmall diameter motoneurons innervate slow oxidative fibersIntermediatesized motoneurons innervate fast oxidativeglycolytic fibersProject from spinal nerve from ventral root Large diameter motoneurons innervate fast branches at terminal each branch contacts dif glycolytic fibersmuscle fibre many cells fused togetherNote Striping patternSize PrincipleA given motoneuron innervates 1 type of Small diameter motoneurons more easily muscleexcited by summated EPSPs than large Large muscles1000s of muscle fibresdiameter motoneuronsTiny muscle10 fibres ex Eye Slow oxidative motor units recruited by Note actual neuromuscular junctionend relatively low levels of excitatory synaptic plateset of synapsesmuch stronger inputconnection btwn axonmuscle fibreFast glycolytic motor units recruited by high levels of excitatory synaptic inputneed more Motor Unit Typedescending signalsThe muscle fibers of a motor unit are all of therecruitment order easy to just sit in a chair w same typeposture3 broad categories of muscle fibersof motor unitsRecruitment OrderOverlap btwn them spectrum1gammamotoneurons smallest sizeSpeed of contractionmetabolismcon
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