4. One could argue that the ionic \"event\" which triggers the sequence of event

Question

4. One could argue that the ionic "event" which triggers the sequence of events leading to cardiac muscle contraction is the appearance of Ca2+ in the cell interior (sarcoplasm). A. Where does this Ca'+ come from in the case of cardiac cells? B. How would your answer to Part A change if we were talking about skeletal muscle? C. Using reasonable values for typical intra- and extracellular Ca2+ concentrations estimate the equilibrium potential for Ca2+ D. Comment on the significance of this calculation in terms of the direction and magnitude of driving forces on Ca2+ to cross the cell membrane. E. Compare the skeletal muscle cell action potential and the cardiac muscle action potential in the context of what the significance of membrane Ca2+ channels is in each case.

Explanation / Answer

calcium comes from the cells internal calcium store present in the sarcoplasmic reticulum but it is not due to nerve stimulation In case of the skeletal muscle , depolarization caused by the nervous stimulation triggers the release of calcium from sarcoplasmic reticulum Due to the influx of 2 calcium ions for 3 sodium ions it creates a negative potential of -90mv inside the cell( equilibrium potential for calcium ions) We can know about the stage in which the cell is present ( depolarization , repolarisation,resting stage or hperpolarisation) Action potential is fast and more in case of cardiac cells compared to skeletal muscles because the calcium channels in the cardiac muscle are activated by changes in the cytosolic calcium concentration changes but as in the case of skeletal muscles the calcium channels are activated by activating calcium dependent calcium release by ryanodine sensitive calcium release Channels in sarcoplasmic reticulum

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