National University Muscle Ph


  1. The calcium channel in the SR is considered to be gated. That calcium channel is specifically -gated. That means that it when the action potential runs along the . The gating of the channel ATP to occur.Meanwhile, on the postsynaptic membrane of the neuromuscular junction there are also gated channels. These are also called receptors. These channels are considered to be -gated. In order to open, it ATP. When these gated channels are open they allow to pass through them.


    1. Please keep in mind that an answer can be used more than once.In a sarcomere there are both actin and myosin filaments. The has tropomyosin associated with it. When a muscle fiber is resting, the tropomyosin blocks the on each actin protein. After calcium is available, tropomyosin is tugged out of the way by . This enables each myosin group to attach to the thin filament with its . When the powerstroke occurs, the myosin protein bends at the on its neck. The powerstroke pulls on the entire so that the Z-lines are pulled inward. In order to do this again, another adenosine triphosphate molecule has to bind to the on the region of the myosin molecule so that the cross-bridge can disconnect. To become re-energized, the head group has to break down the ATP molecule using its function. Throughout this entire time, the region of the myosin molecules are not doing anything but remaining stuck within the to hold all the myosin molecules together.


    1. Examine the steps below and put them in the correct order.

      Calcium unbinds from the troponin
      An action potential is generated in the muscle fiber
      Power stroke carried out by myosin heads
      Calcium ions bind to troponin allowing formation of cross bridges
      DHP receptor changing shape causes calcium ion to be released from the sarcoplasmic reticulum into the cytosol.
      ACh levels rise in the neuromuscular junction
      Myosin heads release and elastic filaments pull filaments back to relaxed position.
      Na+ enters into the muscle fiber through ACh receptor channels.
      Calcium ions are pumped by active transport into sarcoplasmic reticulum
      Action potential travels along sarcolemma and t-tubules causing the DHP receptor to change shape

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