Lecture 7- Resting Membrane Potential

Question 1

how do cells maintain gradients of ions?

Answer 1

by means of primary transport

Question 2

does separating charges require energy?

Answer 2

yes!

Question 3

what do charges move through?

Answer 3

conductors

Question 4

how are charges separated?

Answer 4

insulators

Question 5

what is an electrochemical gradient?

Answer 5

combination of an electrical gradient and chemical gradient.
ions are subjected to an electrochemical gradient will move

Question 6

what does an electrical gradient cause across a cell membrane? in respect to membrane potential

Answer 6

unequal distribution of charges (ions), which therefore ultimately is established by ATPase transporters

Question 7

what is membrane potential measured in?

Answer 7

millivolts (mV)

Question 8

for most cells what is the RMP?

Answer 8

between -20mV and -90mV

Question 9

how can membrane potential change?

Answer 9

due to movement of ions

Question 10

special case of RMP where there is a steady state, what is it?

Answer 10

balance between active transport and leakage of ions

Question 11

how do you measure the membrane potential of a cell?

Answer 11

put one recording electrode into the cytoplasm of the cell, put the other one in the saline bath
voltmeter says the membrane potential

Question 12

how do we word the convention of membrane potential?

Answer 12

inside (-) with respect to outside

Question 13

what is depolarization?

Answer 13

membrane potential (mV) gets closer to zero

Question 14

what is hyperpolarization?

Answer 14

membrane potential (mV) gets further from zero (more negative)

Question 15

what is repolarization?

Answer 15

membrane potential (mV) goes back down after depolarization

Question 16

what is equilibrium potential?

Answer 16

the membrane potential that exactly opposes the steady state electrochemical gradient for an ion
follows the convention “inside with respect to outside”

Question 17

explain equilibrium potential/ reversal potential with an example of K+?

Answer 17

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.

Question 18

what does the nernst equation do?

Answer 18

calculates the equilibrium potential for an ion at 37°C given its concentration gradient

Question 19

what does independence have to do with equilibrium potential?

Answer 19

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+

Question 20

why do we need an equation?

Answer 20

to account for leaky ions and their electrochemical gradients

Question 21

what is not included in the equation? why? (2)

Answer 21

anions (-) (ex. proteins)
Ca++
because their permeability is 0 so it wouldn’t affect the equation

Question 22

Na+ relative permeability is 1 and K+ relative permeability is 50, what does that mean?

Answer 22

K+ is 50x leakier than Na+

Question 23

what does the goldman equation do?

Answer 23

predicts RMP considering
relative permeability of Na+, K+ and Cl-
the concentrations inside and outside the cell

Question 24

what is a normal healthy RMP?

Answer 24

-78mV

Question 25

what would be a cause of -89 mV?

Answer 25

hyperpolarization
severe diarrhea, thus low [K+ out] (2mM K+)

Question 26

what would cause -79 mV RMP?

Answer 26

slight hyperpolarization
causes you to retain water, thus Na+ low, (135mM Na+ out)

Question 27

what would possibly cause Na to be 10,000??? what is the RMP?

Answer 27

when a neuron spikes an action potential
RMP would be +58 mV

Question 28

why cant you always only look at the concentration gradient to see what direction ions will move? (3)

Answer 28

ions are charged so we have to look at electrochemical gradient
equilibrium potential
membrane potential of the cell

Question 29

if the RMP of a cell is -78 mV and ENa is +60 mV, what way will ions move?

Answer 29

into the cell to make the cell more positive (want RMP to be as close to ENa as possible)

Question 30

if the RMP of a cell is -78 mV and ECl is -80 mV, what way will ions move?

Answer 30

into the cell to make the RMP more negative

Question 31

epilepsy: Cl inside is 15 mM, RMP is -76 mV and ECl is -52 mV, where will ions move?

Answer 31

out of the cell to make the cell more (+) for RMP to be closer to ECl