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This is a lab question I cant find the answer in the lab manual or in the text book. What physiological processes in a muscle cause the latent period in a muscle fiber? Please help.

Edit: The latent period is the short delay between the muscle action potential and the beginning of muscle tension development. This is what I'm talking about. I'm sorry I didn't make that clear.

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The action potential causes Ca2+ ions to be released in the cells, that is needed for muscle fiber contraction. There is a small time delay from the arrival of the action-potential until the Ca-ions are released and reach the required concentration in the cell for contraction. On the molecular level there is a protein called troponin (this is bacically located on the actin filament along with tropomyosin and obscures the myosin binding site(s)), that bind calcium and then undergoes conformational change - this also adds up to the delay. After this - the conformational change of troponin - myosin and actin can bind together and contraction can occur through conformational changes. All these binding and conformation changes take a small time to be completed, and thus causes a small delay. Below is a picture about the molecular mechanism ofof muscle contraction taken from this wiki page. The linked wiki page has real good detailed information.

enter image description here

I found this article and where they exactly measured things. To clarify my answer (taken from the linked article):

Electromechanical delay (EMD) was described as a time elapse between the onset of muscle electrical activation and onset of force production, reflecting both electrochemical processes [i.e., synaptic transmission, propagation of the action potential, excitation-contraction (EC) coupling] and mechanical processes [i.e., force transmission along the active and passive parts of the series elastic components (SECs)]

So as for the whole muscle, not for just one cell the delay is caused by the things listed in the above quote - although excitation-contraction (EC) coupling and force transmission (things I have described earlier) take place in every single muscle cell that is in a specific muscle fiber.

Edit 2: I found a good and simple ppt/pdf about AP propagation and muscle contraction here.

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  • $\begingroup$ I think this pretty much sums up the steps necessary from neuro-muscular junction until contraction, but what is the rate-limiting step? Your answer is basically a summing up of events, and not a dedicated answer to the question from m y understanding of PO's intentions. I mean, a chemical synapse is pretty much a 10-ms event if I am not mistaken, so that's not the bottleneck. What is? $\endgroup$ – AliceD Mar 13 '15 at 13:03
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The Latent period is caused by:

  1. Time taken for the stimulus to travel along the nerve to the neuromuscular junction
  2. Time taken for the impulse to cross the neuromuscular junction and to stimulate the muscle
  3. Time taken for the excitation-contraction coupling to occur
  4. Time taken by the lever to overcome the inertia of rest
  5. Time taken to overcome the vicous resistance of the muscle.

The latent period is usually about 10 ms.

enter image description here


Taken from Textbook of Practical Physiology Edition 2, by GK Pal & Pravati Pal

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