Skeletal Muscle - Skeletal Muscle: Responses of Whole...

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Skeletal Muscle: Responses of Whole Muscle Motor Unit: a lower motor neuron and all skeletal muscle fibers stimulated by it Innervation ratio = motor neuron to muscle fibers (motor neuron may stimulate few or thousands of fibers) Control of Strength of Contraction: muscle is “all-or-none” contraction when stimulated For whole muscle contraction: weak contraction= few motor neurons stimulated by CNS Strong contraction = more all at once CNS Control of Muscle Contraction Strength 1) Degree of control can be accomplished by means of innervation ratio Motor units (SMALL AND MANY) – finer degree of control over contraction (eye) (LARGE AND FEW) – lower degree of control (upper leg) 2) Recruitment of Motor Units Somatic motor neurons with small diameter axons innervate fewer muscle fibers Require LESS excitation from CNS Brain activates smallest motor neurons first, which small motor units contract The more force needed the larger motor neurons stimulated/large units contract This is known as RECRUITMENT: mechanism allows CNS to control “graded” response ISOMETRIC contractions = no muscle length shortening, force generated not able to overcome opposing force Occurs when force is too great to overcome/not enough muscle fibers stimulated, start of contraction ISOTONIC contractions = muscle length shortens, force generated is able to overcome opposing load The actual moving of the object
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Senes Elastic Components: tendons (elastic proteins in cartilage and connective tissue) Have some elasticity, able to be stretched and recoil Muscle must first contract enough to begin to overcome load, pull on sense elastic components Muscle will then begin to shorten (like a loose rope, must tighten before u can pull) Types of Muscle Contraction Twitch: full cycle of contraction/relaxation, 7 to 100 milliseconds, contraction/relaxation phase Latent Period: prior to twitch, electrical activity, sliding of filaments, overcoming S.E.C. ^ Graded Response by a Given Whole Muscle Threshold (strength of stimulation required) different for different muscle fibers
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This note was uploaded on 03/31/2008 for the course BIOL 141 taught by Professor Viti,janehartwel during the Fall '08 term at Pennsylvania State University, University Park.

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Skeletal Muscle - Skeletal Muscle: Responses of Whole...

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