Lecture 7- Resting Membrane Potential Flashcards
how do cells maintain gradients of ions?
by means of primary transport
does separating charges require energy?
yes!
what do charges move through?
conductors
how are charges separated?
insulators
what is an electrochemical gradient?
combination of an electrical gradient and chemical gradient.
ions are subjected to an electrochemical gradient will move
what does an electrical gradient cause across a cell membrane? in respect to membrane potential
unequal distribution of charges (ions), which therefore ultimately is established by ATPase transporters
what is membrane potential measured in?
millivolts (mV)
for most cells what is the RMP?
between -20mV and -90mV
how can membrane potential change?
due to movement of ions
special case of RMP where there is a steady state, what is it?
balance between active transport and leakage of ions
how do you measure the membrane potential of a cell?
put one recording electrode into the cytoplasm of the cell, put the other one in the saline bath
voltmeter says the membrane potential
how do we word the convention of membrane potential?
inside (-) with respect to outside
what is depolarization?
membrane potential (mV) gets closer to zero
what is hyperpolarization?
membrane potential (mV) gets further from zero (more negative)
what is repolarization?
membrane potential (mV) goes back down after depolarization
what is equilibrium potential?
the membrane potential that exactly opposes the steady state electrochemical gradient for an ion
follows the convention “inside with respect to outside”
explain equilibrium potential/ reversal potential with an example of K+?
ex. K+ enters the cell through active transport K+ pump, therefore the concentration of K+ is higher inside the cell, they can leak outside the cell through leakage channels so to prevent that we put (-) ions into the cell. so the amount of voltage necessary to keep the K+ inside is called equilibrium potential.
what does the nernst equation do?
calculates the equilibrium potential for an ion at 37°C given its concentration gradient
what does independence have to do with equilibrium potential?
equilibrium potential for each ion is independent of the concentration of other ions
ex. equilibrium potential for K+ doesn’t effect the equilibrium potential for Na+
why do we need an equation?
to account for leaky ions and their electrochemical gradients
what is not included in the equation? why? (2)
anions (-) (ex. proteins)
Ca++
because their permeability is 0 so it wouldn’t affect the equation
Na+ relative permeability is 1 and K+ relative permeability is 50, what does that mean?
K+ is 50x leakier than Na+
what does the goldman equation do?
predicts RMP considering
relative permeability of Na+, K+ and Cl-
the concentrations inside and outside the cell
what is a normal healthy RMP?
-78mV
what would be a cause of -89 mV?
hyperpolarization
severe diarrhea, thus low [K+ out] (2mM K+)
what would cause -79 mV RMP?
slight hyperpolarization
causes you to retain water, thus Na+ low, (135mM Na+ out)
what would possibly cause Na to be 10,000??? what is the RMP?
when a neuron spikes an action potential
RMP would be +58 mV
why cant you always only look at the concentration gradient to see what direction ions will move? (3)
ions are charged so we have to look at electrochemical gradient
equilibrium potential
membrane potential of the cell
if the RMP of a cell is -78 mV and ENa is +60 mV, what way will ions move?
into the cell to make the cell more positive (want RMP to be as close to ENa as possible)
if the RMP of a cell is -78 mV and ECl is -80 mV, what way will ions move?
into the cell to make the RMP more negative
epilepsy: Cl inside is 15 mM, RMP is -76 mV and ECl is -52 mV, where will ions move?
out of the cell to make the cell more (+) for RMP to be closer to ECl
