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  • Module 5.5 Myosin and Muscles continued (Part 4 of mindmaps)
    • 1.
      • Muscle at rest
        • Myosin heads are not attached to binding sites on actin because it is blocked by the tropomyosin
    • 2.
      • Muscle stimulation
        • a nerve impulse depolarises the sarcolemma of the muscle fibres. 
          • Transverse tubules (t-tubules) transmit this depolarisation rapidly throughout the fibres.
    • 3.
      • The role of Calcium
        • ca2+ enter the the myofibril from the sarcoplasmic retiululm. 
          • the ca2+ binds to troponin causing a confrontational change (shape change)
            • Troponin moves the tropomyosin away to unveil actin binding areas
    • 5.
      • Myosin leaves
        • Fresh supplies of ATP bind to myosin heads.
          • This breaks the connection with the binding sites
            • ATP is hydrolysed to ADP+P, which returns myosin heads to starting positions 
              • if calcium is still present the myosin head will bind and kick again
                • the sarcoplasmic reticulum cantians many ca+ pumps
                  • theses pumpca+ out of the sarcoplasm and into the sarcoplasmic membrane
                    • if no other action potential is generated  from motor neurons to sarcolamma then ca+ is immediatly recovered from tropin
                      • Troponin undergoes another conformational change which pulls the tropomyosin back over the actin binding sites
    • 4.
      • Myosin binds
        • myosin heads immediately bind to the available binding sites
          • Myosin releases ADP+P (inorganic phosphate) which causes the myosin head to 'kick back'
            • Actin is pulled towards the centre of the sarcomere (H-zone)


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