Membrane Potentials I and II

Question 1

What is the typical membrane potential of a cell?

Answer 1

-60 mV

Question 2

two basic functions of membrane potentials

Answer 2

storage of energy

generation of action potentials for communication

driving force behind influx of calcium

Question 3

extracellular/intracellular concentrations of Na+

Answer 3

145/10 mM

Question 4

extracellular/intracellular concentrations of K+

Answer 4

5/140 mM

Question 5

extracellular/intracellular concentrations of Cl-

Answer 5

116/4

Question 6

causes of membrane potential

Answer 6

membrane is selectively permeable to K+

K+ leaks out of cells down its concentration gradient

leakage of K+ leaves a net negative charge inside the cell and a net positive charge outside

this generates an electric field, which opposes the opposite of K+

Question 7

ionic equilibrium potential

Answer 7

the membrane potential at which there is no net flux of the ion across the membrane

different for each type of ion

due to a balance of electrical and chemical forces

defined by the Nernst equation

Question 8

Nernst equation

Answer 8

Ei = (RT)/(zF)ln[(Ciout)/(Ciin)]

R = Gas constant (8.314)

T = temperature in K

z = number of elementary charges of the ion in question

F = Faraday constant (96,485)

Question 9

Nernst potential for Na+

Answer 9

+67mV

Question 10

Nernst Potential for K+

Answer 10

-84 mV

Question 11

Nernst potential for Cl-

Answer 11

-84 mV

Question 12

Nernst potential for Ca2+

Answer 12

+125 mV

Question 13

Goldman-Hodgkin-Katz equation

Answer 13

sum of equilibrium potentials for major ions

Question 14

What maintains the membrane potential?

Answer 14

the Na+/K+ ATPase moves 3 Na+ and 2 K+ in per cycle

resting potential occurs when ATPase activity counter-balances the passive fluxes

Question 15

How quickly does potential across a passive membrane change? Why?

Answer 15

exponentially because the membrane acts as a resistor and a capacitor

Question 16

Equivalent Circuit Model

Answer 16

modeling a membrane as a capacitor and a resistor (conductor) in parallel

Question 17

conductance equation

Answer 17

Gion = Iion/(RP - Eion)

Question 18

equation to calculate resting membrane potential using the electric circuit model

Answer 18

Question 19

equation to calciulate membrane potential in terms of permeability

Answer 19

Question 20

permeability

Answer 20

a measure of how many channels are open, does not depend upon ion concentrations

Question 21

response time

Answer 21

rate of change of Vm

has a delay due to Cm

time constant = Rm x Cm

Question 22

stimuli that can alter membrane potential

Answer 22

natural an artificial stimuli

Question 23

natural stimuli

Answer 23

neurotransmitters

hormones

toxins

Question 24

artificial stimuli

Answer 24

elevated extracellular K+ concentrations

intracellular Na+ injection

pharmaceutical agens that are analogs of natural stimuli

Question 25

action potential

Answer 25

a membrane depolarization that reaches a theshold and elicits additional depolarization without further stimulation

Question 26

properties of an action potential

Answer 26

rapid, transient depolarization of the membrane potential that exceeds 0 mV and is followed immediately by a rapid hyperpolarization during of aobut 1-100 msecs

Question 27

absolute refractory period (ARP)

Answer 27

the short period of time after an action potention where a second one cannot be evoked

Question 28

relative refractory period (RFP)

Answer 28

the period of time from the end of the absolute refractory period to the time when new action potentials can be generated

Question 29

Why does the Na+ permeability of the membrane change with depolarization?

Answer 29

Due to the opening of depolarization-gated Na+ channels activation of Na+ channels produces a regenerative increase in Vm

Question 30

What gives rise to the rapid fall of the action potential?

Answer 30

the opening of potassium channels that allows efflux of potassium slightly slower than sodium channels leads to the hyperpolarization of the membranes because it makes the membrane much more permeable to potassium than sodium

Question 31

drugs that modify or block action potentials

Answer 31

Na+ channel blockers k+ channel blockers Ca2+ channel blockers