Membrane potential Flashcards
What is resting membrane potential?
The voltage difference across the cell membrane when the cell is at rest; it establishes a starting point for a cell to be excited
What is the ion concentration of potassium outside and inside the cell?
4.5 mM outside and 155 mM inside
Removing which ion channel from the plasma membrane of a neuron will have the greatest influence on disrupting resting membrane potential?
Potassium leak channels
Which ion channel establishes resting membrane?
Potassium leak channel
How many ions of sodium and potassium does the Na/K ATPase exchange?
3 Na+ go out for 2 K+ to come in
What is the ratio of potassium leak channels to sodium leak channels?
100:1
What is the resting membrane potential for muscle (cardiac/skeletal)?
-80 to -90 my
What is the resting membrane potential for smooth muscle?
-60 my
What is the resting membrane potential for neurons?
-60 to -70 mv
What forces act on ions to develop membrane potential?
Diffusion forces, electrostatic forces and electrochemical forces
What are diffusion forces?
Chemical concentration gradients
What are electrostatic forces?
Electrical gradients (based on charge, opposites attract)
What are Electrochemical forces?
Diffusion forces and electrical forces
What is equilibrium potential?
Membrane potential when electrical and chemical forces equally counteract each other, no further movement occurs (does not equal resting membrane potential) (the voltage/charge required to maintain a specific concentration gradient that allows no movement across the membrane, where chemical forces and electrostatic forces cancel each other out)
Why does sodium have a positive equilibrium potential? Why does potassium have a negative?
Because there is more sodium outside than inside (150mM vs 15mM), the chemical gradient is directing it to move inside the cell, and so the equilibrium potential must be positive (+66mv) to drive sodium out (because like charges repel)
Because there is more Potassium inside than outside so it requires a negative potential (-91 mv) inside to stop movement of potassium going out. (Positive potassium ions will be attracted to the negative charge inside)
Why do sodium and potassium ions have equilibrium potentials not near resting membrane potential?
Because the sodium potassium ATPase keeps sodium and potassium out of equilibrium in resting neurons; this resting membrane potential is necessary for action potential
Which ion does have an equilibrium potential near resting potential?
Chloride
What is the nerve equation?
Equilibrium of an ion = (61.5/z)*Log([x]out/[x]in)
Used to calculate equilibrium potential
What his the driving force? And the equation?
The driving force takes into account electrical and chemical forces to predict movement of ions
It is the resting membrane potential - equilibrium potential
A positive driving force will represent efflux while a negative will represent influx
What are the equilibrium potentials of K, Na, Ca, and Cl?
-91
+61.5
+123
-66.4
What are the estimates for directionality?
Ion in > ion out = log will be negative
Ion in < ion out = log will be positive
Ion in = ion out = log will be zero
Which ions are more permeable and which ones are less?
Potassium is highly permeable (80-86%) while sodium, calcium and chloride are not that permeable
Why does sodium have minimal contribution to the resting membrane potential?
Because of its low permeability
What is the contribution of the sodium potassium atp pump to the resting membrane potential?
4mv (minimal)
How does a positive or negative resting membrane potential influence depolarization?
A more positive RMP will make it easier to depolarize the cell whereas a more negative RMP will make it more difficult (further away from threshold)
What is repolarization?
When the membrane potential is returning towards resting membrane potential?
What are the key properties of action potentials?
All or none
Propagating or self-reinforcing
Non-decremental
What is a graded potential?
Change in membrane potential that is small and local (excitatory or inhibitory) they dissipate with distance because potassium leak channels are always open
How does the strength of initial graded potential correlate with the strength of triggering an event?
Strong triggering event will cause more channels to open and change polarity of a membrane
What phase of an action potential is resting?
Phase 4
What phase of an action potential is depolarization?
Phase 0
What phase of an action potential is repolarization?
Phase 3
What phase of an action potential is hyperpolarization?
It’s the refractory period
What is overshoot?
When the membrane potential is above 0
