Membrane Potentials

Question 1

What is resting membrane potential primarily due to

Answer 1

The permeability of the plasma membrane to potassium ions

Question 2

Resting membrane potentials of cardiac/skeletal muscle, smooth muscle and neurons

Answer 2

Cardiac/skeletal: -80 to -90
Smooth: -60
Neurons: -60 to -70

Question 3

What channels are involved in resting membrane potential

Answer 3

Na/K pump

K+ leak channels

Question 4

Signal gated vs ligand gated channels

Answer 4

Signal gated open in response to intracellular molecule and ligand gated open in response to extracellular molecule

Question 5

Equilibrium potentials of K, Na, Ca, and Cl

Answer 5

K+= -91- equilibrium potential
Na+ = +61.5- equilibrium potential
Ca= 123
Cl= -66

Question 6

Nernst equation when T=37 Celsius

Answer 6

61.5/z * log (x-out/x-in)
Z= charge of ion
Xin/out= concentration of ion inside/outside of cell

Question 7

Ion concentrations of sodium and calcium inside and outside of cell

Answer 7

Sodium inside- 15mM
Sodium outside- 150 mM
Potassium inside- 150mM
Potassium outside- 5mM

Question 8

Driving force

Answer 8

Takes into account electrical and chemical forces to predict the movement of ions
Represents net efflux

Question 9

Driving force equation

Answer 9

Resting membrane potential - Equilibrium potential of ion X

Question 10

Which ion has the highest driving force when a muscle is at rest

Answer 10

Na+ because its equilibrium potential is much further away from the resting membrane potential than other ions

Question 11

What does the goldman equation do?

Answer 11

Allows you to calculate resting membrane potential and takes into account the different equilibrium potentials of ions

Question 12

In order, which ions is the membrane most permeable to, relative to potassium

Answer 12

Chloride- most permeable
Sodium
Calcium- least permeable

Question 13

Sodium contribution to the resting membrane potential

Answer 13

Minimal contribution due to low permeability at rest

Question 14

Phases of the action potential

Answer 14

Resting phase-4
Depolarization-0
Repolarization-3
Hyperpolarization- relative refractory period

Question 15

Calcium ions are important in action potentials in which cells

Answer 15

Cardiac pacemaker cells

Question 16

Depolarization phase described

Answer 16

Increase in permeability of cell to Na
VG Na channels open rapidly
After minimal delay, these channels close automatically

Question 17

Activation/inactivation gate states during resting state, activation state, inactivation state

Answer 17

Resting state- activation gate is close and inactivation gate is open
Activation- activation gate opens during initial depolarization
Inactivation- inactivation gate closes rapidly after activation phase, cannot be moved until membrane potential returns to resting

Question 18

During the refractory period, what is the state of activation/inactivation gates

Answer 18

Activation gate is open, but inactivation gate is swung close, blocking it.

Question 19

When does the positive feedback loop of the opening of Na channels get broken

Answer 19

When the membrane potential reaches +30 because Na channels will close

Question 20

Repolarization phase explained

Answer 20

VG Na channels are closed
Potassium continues to leak out via K+ leak channels
Voltage gates K+ channels slowly open (+35mV to -90mV), further increasing the membrane permeability to K+

Question 21

Hyperpolarization phase explained

Answer 21

Voltage gated K+ channels stay open a little too long
More difficult to stimulate a subsequent action potential
Causes refractory period

Question 22

Absolute refractory period

Answer 22

Na channels activation gate may be open but the inactivation gate is closed and cannot reopen

Question 23

Relative refractory period

Answer 23

Inactivation gate is now open and activation gate is closed
K+ permeability is still fairly high and overshoots K+ leaving the cell so the membrane potential becomes slightly more negative than resting potential
In addition, not all voltage gated Na channels are in the same state at the same time yet, varying the potential response
Action potential may be generated but requires a stronger stimulus

Question 24

Speed of permeability change of Na and K during action potential

Answer 24

Na permeability increases rapidly at first
K+ permeability increases slowly afterwards
Na+ permeability decreases rapidly
K+ permeability decreases slowly

Question 25

Conductance vs permeability

Answer 25

Conductance is charge moving through a membrane whereas permeability indicates a particle that has mass moving

Question 26

Hypokalemic periodic paralysis HypoPP

Answer 26

Periodic dips in blood K+ levels
Drops in blood K+ triggers events, but blood K+ levels are normal between attacks
Membrane hyperpolarized, harder to reach threshold
Repolarization occurs more quickly

Question 27

What is the effect on the driving forces of Na and K when resting membrane potential is decreased to -100mV

Answer 27

Driving force for Na is larger at RMP

Driving force of K is larger at peak

Question 28

Hyperkalemic periodic paralysis

Answer 28

Excessive K+ levels in the blood
Prolonged action potential
Absolute refractory period is lengthened
Attacks managed by mild exercise, potassium wasting diuretics, glucose consumption