L1 Membrane Potential

Question 1

definition of coulomb

Answer 1

measure of electrical charge of a particle

Question 2

how do you apply coulombs to amperes?

Answer 2

a coulomb is the quantity of charge transported in 1 second by a current of 1 ampere

Question 3

what is the proton’s charge in coulombs

Answer 3

e= 1.6 x 10^-19 C

Question 4

what is Avogadro’s number?

Answer 4

number of molecules in one molecule in one mole of any substance = 6.022 x 10^23

Question 5

what is Faraday’s constant?

Answer 5

total charge on a mole of any monovalent ion

Question 6

what is the expected charge on a divalent ion?

Answer 6

2F

Question 7

what is the sign of a charge for cations? for anions?

Answer 7

+, -

Question 8

what is potential difference

Answer 8

the work required to move a unit of charge from one point to another

Question 9

what is the definition of a volt

Answer 9

the energy to move one C one meter

Question 10

how is potential difference always expressed?

Answer 10

in terms of inside of the cell relative to the outside

Question 11

what is the definition of current

Answer 11

net flow of charge

Question 12

what is the unit of current?

Answer 12

ampere

Question 13

what is the unit of an ampere?

Answer 13

coulomb/second

Question 14

in biological systems, current flow is described as the movement of what type of molecule?

Answer 14

movement of positive charges

Question 15

current flow is described as movement of positive charge as measured by the flow from the _____ to the ______

Answer 15

from the anode (positive electrode) to the cathode (negative electrode)

positive electrode denotes all protons go to it
while negative electrode - all electrons go to it

Question 16

what is resistance

Answer 16

the measure of the ease with electrical current flows

Question 17

what is the unit of resistance

Answer 17

an ohm; resistance is abbreviated as R

Question 18

what is Ohm’s law

Answer 18

R=E/I

E is commonly substituted for V

Question 19

the symbol for conductance is

Answer 19

g

Question 20

what is conductance

Answer 20

the reciprocal of resistance

g=I/E

Question 21

inside a typical resting cell, which of these is low in concentration: Cl, K, Na

Answer 21

Inside has low Na and Cl

Question 22

what ion has high extracellular concentrations

Answer 22

Cl, Na

Question 23

will ions pass through a phospholipid bilayer directly?

Answer 23

no, they must pass through a channel

Question 24

as ions pass through the membrane what do they create?

Answer 24

they create concentration gradients

Question 25

why are ions on one side of the phospholipid bilayer able to affect ions on the other side of the phospholipid bilayer?

Answer 25

because the membrane is thin - 5nm thick

Question 26

when is the equilibrium potential reached?

Answer 26

when the ionic gradient is equal to the concentration gradient if you don't understand that - basically its the point where there's no net diffusion of an ion

Question 27

what three things determine the rate of flow of an ion across a plasma membrane?

Answer 27

concentration gradient voltage difference across the plasma membrane conductance of ion channels

Question 28

the membrane of potential where there is no net movement of a specific ion is called what

Answer 28

equilibrium potential of that ion (E_ion)

Question 29

the equilibrium potential of an ion may be calculated by what

Answer 29

Nernst equation

Question 30

what is the Nernst equation for any given ion?

Answer 30

E_ion = [ (RT) / (zF) ] * ln( [ion]_out / [ion]_in )

Question 31

what do R, T, z, F mean in the Nernst equation?

Answer 31

``` R = gas constant T = absolute temperature z = valence of ion F = Faraday constant ```

Question 32

what can we simplify about the Nernst equation at room temperature?

Answer 32

RT/F can be replaced by 58 mV | also natural logarithms (ln) is replaced by base 10 logarithms (log)

Question 33

what is the difference between the Nernst equation at room temperature versus in a mammalian body?

Answer 33

instead of 58mV, it is instead 61mV

Question 34

what is the Nernst equation only valid for?

Answer 34

it is only valid for ions that diffuse and its results describe the net flow of a passively diffusing ion when the system is at equilibrium

Question 35

what is the principle of electrical neutrality

Answer 35

under biological conditions, the bulk concentration of cations in any compartment must equal bulk concentrations of anions in the same compartment tldr: cations must equal anions to be neutral

Question 36

Donnan equilibrium is

Answer 36

state when product of outside ion concentrations equals product of inside ion concentrations e.g. [K+]_out * [Cl-]_out = [K+]_in * [Cl-]_in same as electrochemical equilibrium

Question 37

the Na/K pump is a(n) _______ (active/passive/facilited) pump

Answer 37

active, requires ATP

Question 38

the Na/K pump pushes how many ions of Na/K in/out?

Answer 38

3 Na out | 2 K in

Question 39

why do we have both a Nernst equation and a Goldman equation?

Answer 39

the Nernst equation is to determine the membrane potential of individual ions the Goldman equation takes into account concentration gradients of permeable ions as well as their relative membrane permeabilities for each

Question 40

what is the other name for the Goldman equation

Answer 40

constant-field equation

Question 41

in a membrane's resting state, the relative ionic permeabilities of K, Cl, and Na are?

Answer 41

P_K : P_Cl : P_Na = 1 : 0.45 : 0.02

Question 42

using the Goldman equation and the permeabilities of K and Na, the membrane potential would be?

Answer 42

-71 mV

Question 43

what are some passive membrane properties (3)?

Answer 43

transmembrane resistance axial resistance membrane capacitance

Question 44

how is input resistance (r_in) defined?

Answer 44

r_ in = (delta V) / I where delta V = change in membrane potential I = injected current

Question 45

specific membrane resistance of a unit area (R_m) has units of ?

Answer 45

ohms* cm ^2

Question 46

specific membrane resistance (R_m) is a function of

Answer 46

density of ion channels and their conductance

Question 47

how is the area of the size of a cell related to the resistance?

Answer 47

the larger the area, the smaller the resistance

Question 48

what is the input resistance of an ideal spherical neuron?

Answer 48

R_in = R_m / (4*pi*r^2) , where r is the radius of the cell

Question 49

where does maximum membrane depolarization occur?

Answer 49

at the site of the current injection (or synapse)

Question 50

what does r_i symbolize

Answer 50

it is the longitudinal resistance of intracellular fluid (axial resistance) for a unit length

Question 51

what is lambda and how is it defined?

Answer 51

lambda = length constant = sqrt ( r_m / r_in) it is the point away from the initial site where the V would be 0.37V_0

Question 52

how would you determine the membrane voltage at any point on the membrane distant from the synaptic electronic depolarization?

Answer 52

at given point x away from the site of depolarization, V_x = (V_0) * e^ (-x/lambda) where V_0 = initial site (where max voltage occurs)

Question 53

if x = lambda, what would be V_lambda?

Answer 53

0.37V_0

Question 54

what happens to lambda when r_m gets bigger?

Answer 54

lambda also gets bigger

Question 55

what does a larger lambda mean? how is a larger lambda significant?

Answer 55

larger lambda means less decay over the length | a larger lambda allows for a greater chance for two or more synaptic potentials to summate

Question 56

would you expect a synaptic potential to be larger in a small dendritic process or in a large one? (given that all other things are equal)

Answer 56

a synaptic potential would be expected to be larger in a smaller dendritic process

Question 57

would you expect a larger lambda from a larger dendritic process or a smaller one?

Answer 57

you would expect a larger lambda from a larger dendritic process because they would have less r_in

Question 58

what is tau

Answer 58

tau is defined as the time necessary for the electrotonic potential to decrement to 37% of its original peak value

Question 59

what equation defines tau?

Answer 59

tau = r_m * C_m where r_m = membrane resistance C_m = membrane capacitance

Question 60

how is the duration of tau determined?

Answer 60

V= V_max * e^(-t/tau)

Question 61

what would you expect when t= tau?

Answer 61

V= 0.37V_max

Question 62

if you have a larger tau, would you expect more or less decay over time?

Answer 62

larger tau -> less decay over time