Membrane Potentials Flashcards
What is the concentration of K+ inside and outside of the cell and what is the equilibrium constant?
Outside (small 5)
Inside (large 150)
E(k+)= -91
What is the concentration of Na+ outside and inside the cell and what is the equilibrium constant?
145 Outside
12 Inside
+66 E(Na+)
Which ion channel has the greatest influence on disrupting resting membrane potential? What would have a smaller influence?
Great: Potassium Leak channels
Small: Na-K ATPase
What are the charges on the inside and outside of the cell?
Positive on outside and negative inside
What is the largest factor of resting membrane potential ?
Permeability of potassium ions, allowed by potassium leak channels
What are two important things about the Na/K ATPase channel?
3Na ions are transferred out, while 2K ions are transferred inside,
uses ATP
what is the typical muscle (cardiac/skeletal) resting membrane potential?
-80 to -90 mV
What is smooth muscle normal resting membrane potential?
-60 mV
What is neurons normal resting membrane potential?
-60 to -70 mV
What two forces act on ions to develop the membrane potential? What is both together called?
diffusion forces (chemical gradients/concentration) electrostatic forces (electrical gradients)
both together are electrochemical force
What is equilibrium potential (Eion)?
membrane potential when elctrical and chemical forces are equal, no further movement occurs (not resting membrane potential)
nerst equation to calculate equilibrium potential
61.5/z(charge of ion) x log[x out]/[xin]
How do you calculate the driving force?
Resting membrane potential (Vm) - equilibrium potential (Ex) = driving force
What does the driving force represent?
it takes into accound electrical and chemical forces to predict movement of ions
if IONin > IONout (less than one) what will the log be?
if IONin < IONout (greater than one) what will the log be?
if IONin = IONout (0) what will the log be?
- log will be negative
- log will be positive
- log will be zero
What is the membrane impermeable to?
Calcium!
What happens when extracellular K+ is low and the RMP is more negative?
It is further away from the threshold, so more difficult to depolarize cell (hyperpolarized)
What happens when extracellular K+ is high and RMP is more positive?
It is closer to the threshold, and is easier to depolarize the cell
What do cardiac glycosides inhibit?
Na/K ATPase allowing positive change inside membrane
What is polarization?
deviation from 0mV
What is depolarization?
when membrane potential becomes less negative
What is hyperpolarization?
when membrane potential becoms more negative
what is repolarization?
when membrane potential is returning towards resting membrane potential
What are the 3 key properties of action potentials?
All-or-none
propagating or self/reinforcing
non-decremental (looks the same everywhere)
If there is a small stimulus (graded potentials), will it spread further and quicker on a large or small diameter axon?
Large axon, will not do action potential unless large stimulus.
What are the different phase for resting depolarization repolarization hyperpolarization
resting: phase 4
depolarization: phase 0
repolarization: phase 3
hyperpolarization: refractory period
What happens during depolarization (phase 0)?
voltage gated Na+ channels open activation gate rapidly, and close inactivating gate after minimal delay, causes large positive influx, stopping at +30mV (NA CHANNELS NEED TO BE RESET TO CAUSE AP AGAIN)
What happens during repolarization (phase 3) ?
voltage gated K+ channels open slowly, and K+ leak channels bring K+ back into cell to get back to negative RMP
What happens during hyperpolarization (refractory period)?
voltage gated K+ channels stay open too long, causing excess K+ and negative charge, making it more difficult to stimulate a subsequent actionpotential
What occurs in the absolute refractory period?
Na channels are either open or the inactivation gate is closed and cannot reopen (NA channels not reset so no AP can be generated)
What occurs in relative refractory period?
all Na channels have been reset (inactivation gate is open and activation gate is closed), action potential may be initiated, but requires a stronger stimulus b/c of hyperpolarization
Na permeability during an action potential rapidly increases and decreases, what does K+ permeability do?
Slowly increases and decreases
As extracellular concentration of potassium decreases, the resting membrane potential becomes more negative. As extracellular concentration of potassium increases, the resting membrane potential becomes…?
it becomes more positive
What occurs during hypokalemic periodic paralysis?
dips in blood K+ levels, membrane is hyperpolarized, harder to reach threshold
What occurs during hyperkalemic periodic paralysis?
Excess levels of K+ in blood, closer to threshold, any stimulus makes AP
