Tetanus a smooth sustained contraction of maximal strength caused by twitch

Tetanus a smooth sustained contraction of maximal

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2.Tetanus: a smooth sustained contraction of maximal strength caused by twitch summation before the muscle fiber can relax AT ALL 11
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j.Twitch summation results from a sustained elevation in cytosolic Ca2+ and from increased time to stretch the series-elastic component i.Two factors that contribute to twitch summation1.Sustained elevation in cytosolic Ca2+ permitting greater cross-bridge cycling a.Enough Ca2+ is released in response to a single action potential to interact with all the troponin within the cell, meaning all cross-bridges are free to participate in the contractile response b.These cross bridges continue to cycle as long as enough Ca2+ is present to keep the troponin-tropomyosin complexes away from thebinding sites of on the actin i.A single action potential causes Ca2+ to be released, but as soon as they are released, the Ca2+ATPase starts pumping Ca2+ back into the sarcoplasmic reticulum ii.If action potentials occur quick enough in time, the Ca2+ATPase will not have time to pump all of the Ca2+ backinto the sarcoplasmic reticulum, causing an increase in cytosolic Ca2+ c.As the frequency of action potential increases, the duration of elevated cytosolic Ca2+ concentration increases, and contractile activity increases until a maximum tetanic contraction is reached 2.More time to stretch the series-elastic component a.During a single twitch, the contraction of the muscle fiber doesn't last long enough to completely stretch the series-elastic componentand allow the full tension to be transmitted to the bone b.At the end of one twitch, the elastic elements slowly relaxi.So if another twitch occurs before the elastic element is relaxed, the contraction with be added c.As the frequency of action potentials increases, the tension in the series-elastic component transmitted to the bone progressively increases until it reaches its maximum during tetanus ii.2 main factors of the nervous system for accomplishing gradation of contraction1.Number of motor units stimulated 2.Frequency of motor unit stimulation iii.The areas of the brain that direct motor activity combine tetanic contractions and precisely times shifts of asynchronous motor unit recruitment to execute smooth (rather than jerky) muscle contractions k.There is an optimal muscle length at which maximal tension can be developed i.Optimal length: length at which maximal force can be achieved during a tetanic contraction beginning at that length 1.If tetanus starts when the muscle is at optimal length, then more tension will occur 2.If tetanus starts when the muscle is already undergoing contraction (causing the muscle to be more or less than optimal length0), then less tension will occur ii.Contractile activity of optimal length 1.At optimal length, a maximal number of cross bridges occur between myosin and actin iii.Contractile activity at lengths greater than optimal length 1.When the muscle is lengthened, the thin filaments are pulled out so only the actin still “in the mix” can bind to myosin cross bridges 12
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