exam 1: Ch 6 Membrane Potential

Question 1

membrane potential

Answer 1

difference in charge across membrane

Question 2

Membrane potential results in part from

Answer 2

presence of large anions (phosphates and negatively charged proteins) being trapped inside cell and action of Na+/K+ pumps

Question 3

the membrane is more permeable to? and less permeable to?

Answer 3

more permeable to K+ and less permeable to Na+ which must pumped out

Question 4

what are the diffusable cations that are attracted into cell by the trapped anions (located intracellularly) thus they accumulate within the cell?

Answer 4

K+,mostly, but also Na+ and Ca2+

Question 5

The magnitude of charge difference between the inside and outside of the cell is measured in ?

Answer 5

voltage

- K+ is attracted inside by the trapped anions but also driven out but the [gradient]

Question 6

The electrical properties of cells is based on

Answer 6

on the difference in the [specific ions] and the permeability of the plasma membrane to each of these ions

Question 7

equilibrium potential

Answer 7

theoretical voltage across cell membrane if only 1 ion could diffuse through the membrane
- difference in voltage across the membrane that would exactly balance the diffusion gradient and prevent the net movement of an ion

Question 8

If membrane permeable only to K+,

Answer 8

it would diffuse until reaches its equilibrium potential (Ek)

Question 9

K+ is attracted inside by

Answer 9

trapped anions but also driven out by its [gradient]

Question 10

At K+ equilibrium

Answer 10

electrical & diffusion forces are = & opposite =

-90mV

Question 11

-90mV means

Answer 11

means that the inside of the cell has more negative charge than the outside because at this point there is not enough K+ inside to neutralize charge form the anions

Question 12

voltage difference across the membrane =

Answer 12

POTENTIAL DIFFERENCE
- Please Note: In reality, more than one ion contributes to the resting membrane potential. Equilibrium potential only describes IFF voltage across cell membrane if only 1 ion could diffuse

Question 13

Nernst Equation

Answer 13

allows theorectical equalibrium potential to be calculated if [ion] are known; gives membrane voltage needed to counteract concentration forces acting on an ion

Question 14

Value of equilibrium potential (Ex) depends on

Answer 14

ratio of [ion] inside & outside cell membrane

Question 15

Ex =

Answer 15

Ex = 61 log [Xout]
— ——–
z [Xin]

Question 16

z =

Answer 16

z = valence of ion X

Question 17

For concentrations shown

Calculate EK+ and ENa+

Answer 17

EK+ = 61 log 5
– —–
+1 150 = -90 mV

Question 18

a membrane potential of -90 mv would prevent

Answer 18

K+ from diffusing out of the cell

Question 19

a membrane potential of +60 mV would prevent

Answer 19

Na+ from diffusing into the cell

Question 20

RMP

Answer 20

resting membrane potential

Question 21

resting membrane potential

Answer 21

membrane voltage of cell in unstimulated state; RMP of most cell is -65 to -85 mV

Question 22

RMP depends on

Answer 22

 concentrations of ions inside & out, and on permeability of each ion

Question 23

RMP is affected most by

Answer 23

most by K+ because the membrane is most permeable to it, but some Na+ diffuses in so RMP is less negative than EK+

Question 24

Role of Na+/K+ pumps in RMP

Answer 24

 Because 3 Na+ are pumped out for every 2 K+ taken in, pump is electrogenic
 It adds about -3mV to RMP
 Maintains [] gradients and thus membrane potentials

Question 25

current movement of charged ions

Answer 25

electrical signal of cells