Membrane potential

Question 1

Electric forces are ______ than osmotic forces

Answer 1

way larger

Question 2

Membrane potential

Answer 2

electrical differential across the cell membrane. Empirical

Question 3

Equilibrium potential

Answer 3

calculated from the Nernst equation for a particular ion

Question 4

True or False: Bulk solutions are always electrically neutral

Answer 4

True. This includes inside the cell

Question 5

Nernst equation

Answer 5

Eeq = (62/z)log(Co/Ci)

Question 6

What two forces govern passive movement of an ion across a membrane?

Answer 6

concentration difference and electrical potential difference (combine to make electrochemical gradient)

Question 7

What does the Nernst equation tell us?

Answer 7

the electrical potential difference across the membrane that must exist if the ion is to be at equilibrium at given concentration

Question 8

What is the equilibrium potential when an ion is at equal concentration across a membrane

Answer 8

zero

Question 9

What does it mean when Vm is not the same as Ecl?

Answer 9

• the membrane is impermeable to Cl-
  or
• Cl- must be pumped across the membrane

Question 10

Donna’s rule

Answer 10

[Ko][Clo]=[Ki][Cli]

Question 11

Na/K pump ratio

Answer 11

3 Na+ (out) for 2 K+ (in), making it electrogenic (not electro-neutral

Question 12

How do relative membrane potential depend on permeabilities to ions?

Answer 12

• Na+ is constantly leaking out of the cell trying to get to equilibrium (pulling Vm to Ena) and K+ is leaking out trying to pull Vm down to Ek
• The balance is different in different cells due to relative permeability (how many K+ or Na+ channels they have)
• this determines if Vm is closer to Ena or Ek

Question 13

What is the primary short term determinant of membrane potential?

Answer 13

The relative membrane permeabilities to different ions (even if the Na/K pump stopped working, nothing really happens initially in most cells)

Question 14

What is the driving force of an ion?

Answer 14

the difference between Vm - Ena or Vm - Ek

Question 15

Why do changes in ECF levels of Na+ have little effect on the membrane potential?

Answer 15

the membrane is relatively impermeable to Na+

Question 16

Why are cells very sensitive to K+ ECF changes?

Answer 16

• the cell membrane is much more permeable to potassium
• an increase in [K+] will reduce the efflux of K+ from the cell, causing the cell to depolarize and Ek moves closer to zero
• Because Vm falls between Ek and Ena, there is depolarization -> a modest change in [K+]o results in a large change in Vm

Question 17

What are three treatments for hyperkalemia?

Answer 17

• sodium bicarbonate
• beta-2 adrenergic agonist to increase the activity of the Na-K ATPase pump
• give insulin and glucose to increase ATP supply for the Na-K ATPase pump

Question 18

How is hyperkalemia diagnosed?

Answer 18

usually an EKG to detect cardiac arrhythmia followed by measuring plasma potassium ion concentration