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Neuroscience exam 3

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University at Buffalo
Exercise Science
ES 342

Neuroscience Study Guide Block CThe Motor System Overview Handout 13Overview See chart on p1 handout 13Final Common Pathway lower motor neuronsaLocation in the Ventral HornLateral Fingers armsMedial ShoulderAnterior Extensor MusclesPosterior Flexor MusclesbTypes of Motor NeuronsAlpha Motor NeuronGamma Motor NeuronConcentration7030MyelinationYesYesSizedia of axon1220 um28 umConduction vel70120 ms1050 msTarget innervationsExtrafusal fiberIntrafusalExtrafusal fiber voluntary striated mm generate force and mm activationIntrafusal fiber sensory feedback from mm Contraction no forcehelps maintain reflex as muscleshortenscMotor UnitSingle nerve and all the muscle fibers it innervatesWhen AP travels fibers contractSimultaneous act of all muscle fibers of that nerveSmall ratio of motor units to muscle fibers means there is a precise controlLarge ratiosmeans that there is less precise control16 occulomotor mm1100 hand12000 antigravity mmNoteA single AP traveling down the axon of a lower motor neuron triggers the release of Achat all terminal branches of that axonThus stimulation of a single motor neuron leads to more or less simultaneous activationof all muscle fibers in that motor unitWithin the muscle however fibers of a given motor unit are widely distributeddTypes of Motor UnitsSlow Units redFast Units whiteMitochondrial density toHighLowgen ATPContraction timeLongShortMuscle tension forceLowHighO2 consumptionHigh bc of mitochondriaLowFatigabilityLowHighNoteDifferent muscles contain varying proportions of these motor unitsEach muscle has a combination of fibers that best suits the normal physiological functionof that muscleeCharacteristics of LMN innervating different motor UnitsSlowFastClassificationType I small alpha motorType II large alpha motorneuronneuronAxon sizeSmall 1214Large 1820Firing frequencyLowHighTarget organSlow switch fibersFast twitch fibers
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