My a and P

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 ___________