Lecture 10 Ions and Membrane Potentials

Question 1

Diffusion of Ions

Answer 1

through Ion channels 
down an electrochemical gradient 
electrical potential (measure in millivolts) is electrical force on an ion

Question 2

Electrical potential difference between ICF and ECF is due to

Answer 2

imbalance of + and - charges across the membrane

membrane potential

Question 3

Resting membrane potential is

Answer 3

-70mV (negative inside)

Question 4

Membrane potential

results from?

Answer 4

results from the unequal distribution of permeable ions (K+ and Na+) between the ICF and ECF, and resulting movements of these ions across the membrane

Question 5

Potential difference

Answer 5

potential difference across the membrane of an unstimulated nerve or muscle cells

Question 6

what forms the concentration gradients

Answer 6

the Na+/K+ pump actively transports Na+ out and K+ in

forming concentration gradients of Na+ and K+ ions

Question 7

The resting cell membrane is

Answer 7

permeable to K+ due to the presence of K+ leak channels in the membrane

Question 8

How does K+ move

Answer 8

K+ diffuses out of the cell down its concentration gradient

Question 9

What makes the ICF more negative?

what does this cause?

Answer 9

Movement of K+ out of the cell makes the ICF more negative. The resulting negative electrical potential inside the cell creates an electrical gradient that acts in the opposite direction as the concentration gradient.

Question 10

Equilibrium potential for K+

Answer 10

at some point the concentration gradient and electrical gradient for K+ will exactly counterbalance each other. This point is the equilibrium potential for K+
Ek = -90mV

Question 11

Diffusion of K+ outward

Answer 11

tends to move the membrane potential toward Ek

since the resting membrane is most permeable to K+, the RMP is close to Ek

Question 12

Resting Membrane

Answer 12

is slightly permeable to Na+ so some Na+ diffuses inward

this makes the RMP slightly less negative than Ek

Question 13

Equilibrium potential of an ion

Answer 13

is the potential difference at which the electrical force exactly balances the chemical force (concentration gradient) on the ion

The EP of an ion can be calculated using the Nernst equation

Question 14

Nernst Equation

Answer 14

Eion=60/z * log(cout/cin)

Eion is the equilibrium potential of the ion in millivolts (mV)
Z is the charge on the ion (1+ for K+ and Na+)
Cout and Cin are concentrations of the ion in the ECF and ICF
log is the base 10 logarithm

Question 15

ENa

Answer 15

+60mV

Question 16

What determines the membrane potential

Answer 16

the concentration gradients of permeable ions, primarily Na+ and K. Formed by the Na+/K+ pump

The relative permeability of the membrane to these ions (K+ vs Na+) due to specific ion channels

Question 17

What has the largest influence on RMP

what does it create

Answer 17

K+ has the greatest influence on RMP because the resting membrane is most permeable to K+
K+tends to move out of the cell which creates a negative potential inside the cell

Question 18

Main factors of the RMP

Answer 18

RMP is close to Ek, but is slightly less negative because of some inward Na+ leakage
RMP is very sensitive to changes in K+ in the ICF or ECF
RMP is only slightly affected by Na+ because the resting membrane is not very permeable to Na+

Question 19

The membrane potential results from

Answer 19

the unequal distribution of permeable ions (K+ and Na+) between the ICF and ECF and the resulting movements of these ions across the membrane

Question 20

what forms the gradients and what happens once the gradients are in place

Answer 20

The Na+/K+ pump forms concentration gradients of K+ and Na+ between the ICF and ECF. Once these gradients are in place the membrane potential depends on the relative permeability of the membrane to K+ and Na+ which is determined by specific ion channels.

Question 21

What will permeable ions do

Answer 21

Ions that are permeable will diffuse across the membrane down their electrochemical gradients, which moves the membrane potential toward the equilibrium potential of the most permeable ion(s).

Question 22

What is dominant is a resting cell

Answer 22

K+ leak channels are dominant so RMP is close to Ek

Question 23

How does the membrane potential change

Answer 23

the membrane potential can change very rapidly in response to changes in permeability of the membrane to Na+, K+, or other ions. Changes in permeability to these ions result from opening or closing of different ion channels.