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The Nervous System: Membrane Potential
1.Record the intracellular and extracellular concentrations of the following ions (mM/L):

| Intracellular| Extracellular|
Sodium (Na+)| 15| 150|
Potassium (K+)| 150| 5|
Chloride (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+? Use arrows to indicate the change in permeability. a. An increase in the number of passive K+ channels up

b. Opening of voltage-gated K+ channels up
c. Closing of voltage-gated K+ channels down
4.a. What acts as a chemical force that pushes K+ out of the cell? Concentration gradient b. What force tends to pull K+ back into the cell? Electrical potential 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 gradients in question 4 promote or oppose the movement of Cl– into the cell? a. Promote
b. Oppose
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 compensates for the movement (leakage) of Na+ and K+ ions? Sodium potassium pump 10.What will happen to the resting membrane potential of an excitable cell if: (Write pos or neg to indicate which way the membrane potential would change.)

a. extracellular fluid concentration of K+ ___________
b. extracellular fluid concentration of K+ ___________
c. extracellular fluid concentration of Na+ ___________
d. number of passive Na+ channels ___________
e. open voltage-gated K+ channels ___________
f. open voltage-gated Na+ channels ___________
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