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Originally Posted by Powel6016
Hey,
What happens when adequate ATP is present within the muscle fiber, but action potentials occur at a frequency so great that calcium ions are not transported back into the sarcoplasmic reticulum between individual action potentials?
Please help, anything would be helpful. This is for my anatomy class. 
Peace,
Justin |
Let me try this off the top of my head, then I'll check to see if I got it right (it's been about 6 years since I've had A&P I).
If the action potentials arrive too fast for calcium levels to return to normal in between impulses, but some Ca2+ ions are still reclaimed by the sarcosplasmic reticulum via active transport, then the tension produced by the muscle fiber will continue to increase during each contraction until reaching a maximum: I believe this is called treppe. But if action potentials arrive even faster, I believe it is called complete tetanus.
Okay, let me check. Looks like I got the first part correct...
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"Treppe
If a skeletal muscle is stimulated a second time immediately after the relaxation phase has ended, the contraction that occurs will develop a slightly higher maximum tension than did the contraction after the first stimulation. The increase in peak tension indicated in Figure 10-15a will continue over the first 30-50 stimulations. Thereafter, the amount of tension produced will remain constant. Because the tension rises in stage, like steps in a staircase, this phenomemon is called treppe, a German word for "stairs". The rise is thought to result from a gradual increase in the concentration of calcium ions in the sarcoplasm, in part because the ion pumps in the sarcoplasmic reticulum are unable to recapture the ions in the time between stimulations." (Fundamentals of Anatomy & Physiology: Sixth Edition, Frederic H. Martini, Benjuamin Cummings/Pearson Education, 2004, p309)
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And my second part was also correct (though scant on info)...
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"Complete tetanus
Complete tetanus is obtained by increasing the stimulation rate until the relaxation phase is eliminated. During complete tetanus, action potentials arrive so rapidly that the sarcoplasmic reticulum does not have time to reclaim the calcium ions. The high Ca2+ concentration in the cytoplasm prolongs the contraction state, making it continuous. Vritually all normal muscular contractions involve complete tetanus of the participating muscle fibers." (Fundamentals of Anatomy & Physiology: Sixth Edition, Frederic H. Martini, Benjuamin Cummings/Pearson Education, 2004, p309)
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However, I forgot about the intermediate case called incomplete tetanus.
Calcium ions and Muscle Fibers
