lecture7-11

lecture7-11 - Lecture 7-skeletal Mechanics Lecture...

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Single muscle fiber: the muscle produces tension to exert a force on the load. •if tension > load, the muscle will shorten ( isotonic contraction •If the fiber generates tension, but does not shorten (load > tension), this is isometeric contraction . lengthening contraction occurs when the muscle generates tension but still lengthens because the load > tension (such a lowering a heavy object). Why is this important? Because cross-bridging cycles in these three types of contractions is different . •Only in the isotonic contraction do the Z lines move together (and the fiber shortens). •A muscle fiber can be activated, the myosin can go through repeated rounds of ATP hydrolysis and actin binding and release, without actually moving the Z-lines closer. But tension is still generated by the actin and myosin. Lecture 7-skeletal muscle mechanics not surprisingly, the heavier the load on a muscle, the slower is the shortening velocity load
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myoplasmic [Ca 2+ ] twitch force (tension) time (msec) contraction time •a single action potential results in a sub-maximum contraction ( twitch ). Myoplasmic [Ca 2+ ] falls before maximum contractile force is obtained. myoplasmic [Ca 2+ ] Repeated Action Potentials can be Summated: tetanus force • a maintained contraction in response to repeated stimulation is called tetanus •the action potential is very brief compared to the duration of the contraction •there is a short latent period between the end of the action potential and the onset of tension. •the length of the contraction time varies with muscle fiber type (see later in lecture). •if action potentials occur rapidly enough, saturating [Ca 2+ ] is achieved and maximum force is generated. Factors that regulate the strength of a single fiber contraction (twitch). •action potential are all or none, so size of action potential not a factor • rather, strength of contraction is controlled by the frequency of action potentials •repeated, but slower deploarizations will not give fused tetnus, but can be added to increase force: action potential
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The force generated by a muscle fiber depends upon its length: •maximum force is generated when maximum cross bridges are formed: too short , thin filaments overlap, heavy chains hitting Z-lines.
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This note was uploaded on 02/14/2011 for the course MCDB 111 taught by Professor Smith during the Spring '11 term at UCSB.

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lecture7-11 - Lecture 7-skeletal Mechanics Lecture...

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