Membrane Potentials Flashcards
What is resting membrane potential primarily due to
The permeability of the plasma membrane to potassium ions
Resting membrane potentials of cardiac/skeletal muscle, smooth muscle and neurons
Cardiac/skeletal: -80 to -90
Smooth: -60
Neurons: -60 to -70
What channels are involved in resting membrane potential
Na/K pump
K+ leak channels
Signal gated vs ligand gated channels
Signal gated open in response to intracellular molecule and ligand gated open in response to extracellular molecule
Equilibrium potentials of K, Na, Ca, and Cl
K+= -91- equilibrium potential Na+ = +61.5- equilibrium potential Ca= 123 Cl= -66
Nernst equation when T=37 Celsius
61.5/z * log (x-out/x-in)
Z= charge of ion
Xin/out= concentration of ion inside/outside of cell
Ion concentrations of sodium and calcium inside and outside of cell
Sodium inside- 15mM
Sodium outside- 150 mM
Potassium inside- 150mM
Potassium outside- 5mM
Driving force
Takes into account electrical and chemical forces to predict the movement of ions
Represents net efflux
Driving force equation
Resting membrane potential - Equilibrium potential of ion X
Which ion has the highest driving force when a muscle is at rest
Na+ because its equilibrium potential is much further away from the resting membrane potential than other ions
What does the goldman equation do?
Allows you to calculate resting membrane potential and takes into account the different equilibrium potentials of ions
In order, which ions is the membrane most permeable to, relative to potassium
Chloride- most permeable
Sodium
Calcium- least permeable
Sodium contribution to the resting membrane potential
Minimal contribution due to low permeability at rest
Phases of the action potential
Resting phase-4
Depolarization-0
Repolarization-3
Hyperpolarization- relative refractory period
Calcium ions are important in action potentials in which cells
Cardiac pacemaker cells
Depolarization phase described
Increase in permeability of cell to Na
VG Na channels open rapidly
After minimal delay, these channels close automatically
Activation/inactivation gate states during resting state, activation state, inactivation state
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
During the refractory period, what is the state of activation/inactivation gates
Activation gate is open, but inactivation gate is swung close, blocking it.
When does the positive feedback loop of the opening of Na channels get broken
When the membrane potential reaches +30 because Na channels will close
Repolarization phase explained
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+
Hyperpolarization phase explained
Voltage gated K+ channels stay open a little too long
More difficult to stimulate a subsequent action potential
Causes refractory period
Absolute refractory period
Na channels activation gate may be open but the inactivation gate is closed and cannot reopen
Relative refractory period
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
Speed of permeability change of Na and K during action potential
Na permeability increases rapidly at first
K+ permeability increases slowly afterwards
Na+ permeability decreases rapidly
K+ permeability decreases slowly
Conductance vs permeability
Conductance is charge moving through a membrane whereas permeability indicates a particle that has mass moving
Hypokalemic periodic paralysis HypoPP
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
What is the effect on the driving forces of Na and K when resting membrane potential is decreased to -100mV
Driving force for Na is larger at RMP
Driving force of K is larger at peak
Hyperkalemic periodic paralysis
Excessive K+ levels in the blood
Prolonged action potential
Absolute refractory period is lengthened
Attacks managed by mild exercise, potassium wasting diuretics, glucose consumption
