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BIOL 273L (31)


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Heidi Engelhardt

COMPLETE BIOL 273L STUDY QUESTIONS Lab 11How is the generation of a potential in this experiment similar to the way in which a resting membrane potential is generated in a living neuron In the experiment the artificial membrane is permeable to cations but impermeable to anionsTherefore when 2 subchambers contain different KCl concentrations K ions from the subchamber with a higher KCl concentration will diffuse through the membrane to the subchamberwith a lower KCl K ions will flow down its concentration gradientThis outflow of cations from one subchamber will result in a membrane difference between the 2 subchambers the subchamber containing greater KCl will have a negative potential readingSimilarly in a living neuron K ions are found in a higher concentration inside the nerve cell than outside and Na ions are found in a higher concentration outside the cell than insideHowever since Na ions cannot diffuse across the cell membrane as well as K ions K ions are able to diffuse out of the cell but Na cannot diffuse in resulting in a slight positive charge on the outer surface of the cell slight negative charge inside the cell called the resting membrane potential RMP difference between the intracellular fluid and extracellular fluid2How is the generation of a potential in this experiment different from the way in which a resting membrane potential is generated in a living neuronK is the major cation inside the cell and Na is the major cation in the extracellular fluid of a living neuron and Cl is dominant in the extracellular fluid as well whereas in the experiment each subchamber representing the intracellular and extracellular fluid of a living neuron contains an equal ratio of K to Cl ions but in different concentrations for the different subchambersUnlike the experimental cell living neurons deal with more than just K and Cl ionsIn a living neuron the cells are not only permeable to cations they are just much more permeable to K 2ions compared to Na Ca and Cl ionsTherefore the Nernst equation would not be an accurate way of calculating the membrane potential of a real cell since the Nernst equation only deals with the permeability of 1 ion whereas living cells are permeable to several ions instead the Goldman equation must be used as it takes into account all ions presentThere is no NaK ATPase pump present in the experimental cell which helps maintain a resting membrane potential by keeping the inside of the cell or 1 subchamber more negative than outside
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