L2 - Membrane Potential (Chapter 5 Cont.)

Question 1

What is resting membrane potential?

Answer 1

• the weighted avg of the voltage of a membrane
• somewhere btwn the resting potentials for Na and K
• generally -70mV

Question 2

How is the resting membrane potential calculated? Why is this equation used?

Answer 2

• the goldman equation
• accounts for multiple ions and for ion permeability

Question 3

What is the Goldman Equation calculating?

Answer 3

calculates the potential at which the membrane is the most permeable to all of the ions in the equation

Question 4

Why is the Goldman equation used for calculating resting membrane potential rather than the Nernst equation?

Answer 4

• the Nernst equation only accounts for one ion, and it assumes the ion is freely permeable

Question 5

What is permeability? How does permeability affect an ion’s influence on membrane potential?

Answer 5

• The ease with which a molecule can pass through the cell membrane
• the passage of ions can either depolarize of repolarize the cell

Question 6

What are the ratios of permeabilities of Na, K, and Cl?

Answer 6

• membrane is 100X more permeable to K than Na, and 50X more permeable to Cl
• membrane is 2X more permeable to Cl than Na

Question 7

What are the physiological consequences of the difference in permeability ratios of Na, K, and Cl?

Answer 7

• K has the biggest influence on the membrane potential bc the membrane is most permeable to K
• more K is going into the cell, depolarizing it, bringing it further away from an AP

Question 8

Explain why the membrane potential calculated using the Goldman equation is expected to be slightly different from experimentally measured values

Answer 8

• the goldman equation doesn’t factor in the passive diffusion of ions
• EX: Na/K pump contributes to about -4mV that is not calculated using the goldman equation