#KYJ. Action potential & depolarisation of muscles. First watch the short video- The Twitching Frogs legs. Then come back and read this to help understand this process. To understand this we need to go back to the basics of cell membrane excitation and a concept called the Action Potential. Cells have a membrane that acts like a complex gate allowing ions (electrolytes) in and out of the cell to alter the electrical charge on the membrane surface. Inside cells there is high potassium and the resting muscle cell is slightly negatively charged (-70—-80mv). Outside cells, it is more sodium rich. When the salt (Sodium) is sprinkled on the fresh frogs legs, the concentration of sodium is so high, that sodium rushes into the cell. In fresh meat there is still enough stored ATP (energy) in the muscle cells to open up the sodium ion channels in the muscle cell membranes. Sodium continues to rush into the cell exchanging with potassium, and for a short time making the cell positively charged... This exchange of ions is called an action potential. Or more commonly we say that the cell depolarises and causes the muscle cell to contract. Lots of contraction=twitching. It is short lived, because it takes ATP to repolarise (reset) as sodium has to be actively pumped out of the membrane (making it negatively charged again). This function of the cell is called the sodium/potassium pump, it needs ATP, which is manufactured by all cells from glucose (usually) and a ready supply of oxygen. These frog legs have no oxygen or glucose supply, so in a few seconds the process stops due to no more ATP.
Posted on: Sun, 04 Jan 2015 20:23:52 +0000
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