Metabolic Sequence: in Muscle Contraction and Relaxation

---

- Discussion:
    - muscle contraction is initiated w/ release of ionic calcium, from terminal
          cisternae into the sarcoplasm;
    - complexing of calcium by troponin shifts the protein conformations in thin
          filament & allows formation of crossbridges between actin & myosin, which
          then moves the actin molecule up long axis of the myosin filament;
    - thick & thin filaments comes from cross-bridges undergo a conformational
          change which end up pulling thin filaments past the thick filaments;
    - as long as the calcium concentration in the cell is maintained in
          range of 10-6 M, the myosin ATPase remains active permiting the fibril to
          stay in its contracted form;
    - when energizing impulse terminates, Ca is rapidly pumped out of sarcoplasm;
    - as ionic concentration drops, calcium is withdrawn from troponin, and
          when sufficiently low, the ATPase on myosin is inactivated;
          - the troponin-actin-tropomyosin B complex again impedes the crossbridging
                between actin and myosin;