6. Work your way through Fig 5-23. Then answer the following questions: A. What
ID: 150920 • Letter: 6
Question
6. Work your way through Fig 5-23. Then answer the following questions: A. What happens to the resting membrane potential of a cell if the extracellular K' concentration increases? It becomes more positive/It becomes more negative/It does not change B. If cell with a resting membrane potential of -70mV was made freely permeable to Na+ which way would Na+ move? Would the membrane potential become more positive or more negative? C. ECL-was calculated as-63mV. Assuming that the resting membrane potential is-70mV, which way will Cl-move when the cell becomes permeable to Cl-? Which gradient, concentration/electrical is stronger? C. Why is the resting membrane potential for a neuron not exactly equal to EK+? D. A nerve fiber is placed in a bathing solution similar to the ECF. After equilibration, a microelctrode placed into the nerve fiber records a membrane potential of-70mV. Assuming Nat, CI-, and K+ were distributed between ECF and ICF to yield the following equilibrium potentials: ENa+ 40, EC)--78mV and EK+ =-84mV, which of these ions seems to be most permeable to the cell membrane of the nerve?Explanation / Answer
6. A. Membrane potential is the disequilibrium between ECF (Extra Cellular Fluid) and ICF (Intra Cellular fluid). ECF is slightly positive and ICF is slightly negative. So when K+ concentration increases in ECF, it further increases the positive charge and it become more positive.
B. If the membrane is made freely permeable to Na+, the these ions will move from ECF to ICF to nullify the electrical disequlibrium (0 mV). So the membrane potential will become more positive.
C. To achieve -70 mV from -63 mV, the electrical disequilibrium should increase. When the membrane become permeable to Cl-, the ions should move from ECF to ICF. Thus the electrical charge of ICF becomes more negative (stronger) and the resting membrance potential becomes more negative or reaches -70 mV.
D. As the resting membrane potential is -70 mV, whichever equilibrium potential is nearer to -70 mV has the highest permeability.
ENa+ => |-70-40| = 110
ECl- => |-70-(-78)| = 8
EK+ => |-70-(-84)| = 14
So the permeability is in the below order.
Cl- > K+ > Na+
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