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Chapter 26

Chapter 26. Muscle Physiology. Muscle activity. The muscle contraction is dependent of: Electrical excitation of a muscle cell Excitation-contraction coupling Sliding of the myofilaments. Action potential. Resting membrane potential -60 to -90 mV K concentration Na concentration

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Chapter 26

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  1. Chapter 26 Muscle Physiology

  2. Muscle activity The muscle contraction is dependent of: • Electrical excitation of a muscle cell • Excitation-contraction coupling • Sliding of the myofilaments

  3. Action potential • Resting membrane potential • -60 to -90 mV • K concentration • Na concentration • Depolarization • Action potential • Repolarization • Absolute refractory period • Relative refractory period

  4. Muscle contraction • Cyclic process beginning with calcium released from SR • Calcium binds to troponin • Changes in troponin shape • Tropomyosinuncovers active site on actin • Actin forms cross-bridges with myosin • Slinding of myosin and actin over each other

  5. Muscle contraction • Muscle shortens • Ending of action potential • Calcium is reabsorbed by sarcoplasmic reticulum • Myosin detaches from actin • Muscle is in resting stage again

  6. Muscle Contraction

  7. Muscle contraction

  8. Muscle Contraction

  9. Muscle contraction • Twitch • Cycle of contraction, relaxation produced by a single stimulus • Phases • Latent period • Contraction phase • Relaxation phase • Threshold stimulus • It is the voltage at which the first contractile response occurs

  10. Muscle contraction • Subthreshold stimuli • All stimuli applied prior to the threshold stimulus • Graded potential • Graded muscle response to increased stimulus intensity • Maximus stimulus • Weakest stimulus at which all muscle cells are being stimulated

  11. Muscle contraction • Treppe or staircase phenomenon • Stimulus is kept at same intensity • Height of individuals spikes increase in a stepwise manner • Repeated stimulation after relaxation phase has been completed • Subsequent contractions are more vigorous

  12. Treppe Caused by: • Increased Ca levels from previous contractions • Increased heat generated by muscle work increases enzyme efficiency

  13. Increased stimulus frequency Repeated stimulation before relaxation phase has been completed will cause: • Wave summation • one twitch is added to another • The intensity of the stimulus is kept the same • The frequency of the stimulus applied increases

  14. Increased stimulus frequency • Incomplete tetanus • Muscle in peak tension. State of sustained fluttering contraction. • Complete tetanus • Relaxation phase is eliminated • There is fusion of twitches

  15. Effects of Repeated Stimulations

  16. Muscle fatigue • Fatigue • Loss of the ability of a muscle to contract • Caused by deficit of ATP • Build up of lactic acid • Lower tissue pH • Exhaustion of energy resources

  17. Effect of the load on the skeletal muscle • Increased load beyond optimum level causes overstretch of the muscles : • The fillaments do not overlap anymore • It will not allow contraction to happens

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