Nervous System I: Membrane Potential - Self Test

NOTE: This quiz is designed to be completed using the InteractivePhysiology CD that you used in the Muscle Lab.  However, you should be able to answer most of the questions without the CD by using your class notes and your textbook.

1. Record the intracellular and extracellular concentrations of the following ions (mM/L):

Ion Intracellular Conc. Extracellular Conc.
Na+ 15 150
K+ 150 5
Cl- 10 125

2. Excitable cells, like neurons, are more permeable to ____K+__ than to ___Na+___.

3. How would the following alterations affect the membrane permeability to K+? (Increase, decrease, unchanged)

                    a. An increase in the number of passive K+ channels __Increase_________

b. Opening of voltage-gated K+ channels __Increase_________

c. Closing of voltage-gated K+ channels __Decrease_________

  • 4.   a. What acts as a chemical force that pushes K+ out of the cell? _Chemical (concentration) gradient of K+________________
  • b. What force tends to pull K+ back into the cell? __Electrical gradient of K+_______________________

    5. When the two forces listed above are equal and opposite in a cell permeable only to K+, this is called the __Equilibrium___ potential for K+ which is __-90_________ mV.

    6. In an excitable cell, also permeable to Na+ and Cl-, the gradients mentioned

    in question 4 would both tend to move Na+ ___into________ the cell.

    7. Would the two gradients in question 4 promote or oppose the movement of Cl- into the cell?

        a. (Gradient a) - Chemical gradient of Cl- would promote movement of Cl- into the cell

        b. (Gradient b) - Electrical gradient of Cl- would oppose movement of Cl- into the cell

    8. Since the neuron is permeable to Na+ as well as K+, the resting membrane potential is not equal to the equilibrium potential for K+, instead it is ____-70_______ mV.

    9. What opposes the movement (leakage) of Na+ and K+ ions?
    __Na-K ATPase Pump_______________________

    10. For each of the following conditions, will the resting membrane potential of an excitable cell become more positive or more negative: (Write pos or neg to indicate which way the membrane potential would change.)

    a. extracellular fluid concentration of K+ decreases __negative_________

    b. extracellular fluid concentration of K+ increases __positive_________

    c. extracellular fluid concentration of Na+ increases __positive_________

    d. open voltage-gated Na+ channels increases ___positive________