Resting Membrane and action potentials Flashcards
Resting ion conditions of a skeletal muscle cell
inside:
150mM K
15mM Na
0.001 Ca
outside:
5 mM K
150 Na
1 Ca
Resting membrane Potential is primarily due to?
the permeability of the Potassium Ions
What is the resting membrane potential for some cells
Muscle (cardia/skeletal): -80 to -90 Smooth muscle: -60 Neurons: -60 to -70 Astrogila: -80 to -90 Erythrocytes: -9mV
What pumps and channels are important in maintain a resting membrane potential
Na/k ATPase
K leak channels
these are Ion channels that form gated pores
Na/K ATPase channel
maintains concentrations in proper place
exchanges 3 Na+ ions to the outside of cell in exchange for 2K+ ions to the inside of the cell
requires ATP
K+ leak channels
Open all the time
K+ leak channels are present at 100:1 ration to the Na+ leak channels
Passively move K+ is more likely to leave the cell than Na to enter
allows for K permeabillity to the plasma membrane
Forces acting on Ions to develop Membrane Potential
Diffusion forces: Chemical gradients
Electrostatic Forces: Electrical
charge base opposite attracts
These two make up the Electrochemical Forces
Equilibrium potential (Eion) Membrane potential when electrical and chemical forces are equal, no further movement occurs
Nerst Equation
61.5/z times the log( [X]out/[X]in)
used to calculate the equilibrium potential
Driving Force
Resting membrane potential Vm - Eion
this represents the net efflux
Driving force takes into account the electrical and chemical forces to predict movement of the ions
IONin is greater than the IONout
IONin is less thatn the IONout
If IONin is equal to the IONout
the log will be negative
the log will be positive
the log will be zero
Always take into account the ion charge (+/-)
At resting membrane why cant NA+ get into the cell if it has an influx driving force
Because the membrane is mostly impermeable to the NA+ at rest
Goldman Equation
This is an equation that helps us determine the membrane potential by taking into account all the different ion concentrations and permeabillity
What are the three main contributions to the resting membrane potential
Contribution of K+ Diffusion potential: this is the main contributor to resting membrane potential
Contribution of the Na+ Diffusion: very minimal due to low permeability at rest
Contribution of Na+/K+ ATP pump: Indirectly contribution to maintain ion concentration gradients
If the Resting membrane potential is more positive, does it make it easier to depolarize?
If the RMP is more positive, it is easier to depolarize because it is closer to the threshold
if the RMP is more negative, it males it harder to depolarize the cell, (hyperpolarized and further away from the threshold)
What are some factors that influence the Potassium Distribution that plays an important part in RMP
Enhance cell uptake: Insulin B-Catecholamines Alklosis Hyperosmolality Strenous exercise
Impair cell uptake: A-Catecholamines Acidosis External potassium balance Cell damage
Polarization
Deviation from 0 mV
Depolarization
when membrane potential becomes less negative
this does not mean action potential because it needs to get to that threshold to get an action potential
Hyperpolarization
when the membrane potential becomes more negative
Repolarization
when membrane potential is returning towards resting membrane potential
Key properties of action potentials
All or None
propagating or self reinforcing
non decremental
Graded Potentials
Changes in membrane potential that are small and local
can be both excitatory or inhibitory
Graded potential dissipate with distance because K+ leak channels are always open
Dependant on the stimulus and radius
strength of initiation is correlated with the strength of triggering event
Phases of Action Potentials: Resting phase
Phase 4
Phases of Action Potentials: Depolarization
Phase 0
Phases of Action Potentials: Repolarization
Phase 3
Phases of Action Potentials: Hyperpolarization
Refractory period
What are the key players in an action potential
Na+ ions K+ ions Voltage-gated Na+ channels Voltage-gated K+ channels K+ leak channels
Ca+ are important in some cell types
How do the Voltage Na+ gates work
Resting: the activation gate is closed and the inactivation gate is open
Activation: the activation gate opens during initial depolarization and Na+ comes into the cell
Inactivation: inactive gate closes rapidly after the inactivation phase after a certain period of time
this inactivation gate will stay closed until the membrane potential returns
What is the positive Feedback loop of voltage gated Na+ channels
Local triggering even occurs which opens some channels and if the event is large enough there will be a great wide area of increased membrane potential
more Na+ channels open and more Na+ flows through
this whole process stops at +30 mv because the Na+ channels close
What happens during the repolarization phase
Voltage gated Na+ channels are closed
Potassium leaks out still via the K+ leak channels
Voltage gated channels slowly open to further increase the membrane permeabillity to K+
this helps to repolarize the cell
What happens during the Hyperpolarization phase
Voltage gated K+ channels stay open a little too long which causes the increased repolarization
THis makes it more difficult to stimulate the next action potential
this is considered the refractory period
Absolute refractory period
Na+ channels are either open or the inactivation gate is closed and cannot reopen
Another action potential cannot be generated
(the mountain on the graph)
Relative Refractory period
Inactivation gate is now open and activation gate is closed
K+ permeabillity is still fairly high so there is hyperpolarization of the resting membrane potential
Not all Na+ voltage gates are in the same state
An action potential can still happen at this time, but requires a stronger stimulus
Hypokalemic Periodic Paralysis (hypoPP)
Periodic dips in blood K+ levels
Drops in blood K+ levels triggers events, but blood K+ levels are normal between attacks
Membrane hyperpolarized, harder to reach threshold
repolarization occurs more quickly
Hyperkalemic Periodic Paralysis
Excessive K+ in blood
Prolonged action potential and absolute refractory periods lengthened
these can be managed by mild excersise, potassium wasting diruetics, and glucose consumption
