L1 Membrane Potential Flashcards
definition of coulomb
measure of electrical charge of a particle
how do you apply coulombs to amperes?
a coulomb is the quantity of charge transported in 1 second by a current of 1 ampere
what is the proton’s charge in coulombs
e= 1.6 x 10^-19 C
what is Avogadro’s number?
number of molecules in one molecule in one mole of any substance = 6.022 x 10^23
what is Faraday’s constant?
total charge on a mole of any monovalent ion
what is the expected charge on a divalent ion?
2F
what is the sign of a charge for cations? for anions?
+, -
what is potential difference
the work required to move a unit of charge from one point to another
what is the definition of a volt
the energy to move one C one meter
how is potential difference always expressed?
in terms of inside of the cell relative to the outside
what is the definition of current
net flow of charge
what is the unit of current?
ampere
what is the unit of an ampere?
coulomb/second
in biological systems, current flow is described as the movement of what type of molecule?
movement of positive charges
current flow is described as movement of positive charge as measured by the flow from the _____ to the ______
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
what is resistance
the measure of the ease with electrical current flows
what is the unit of resistance
an ohm; resistance is abbreviated as R
what is Ohm’s law
R=E/I
E is commonly substituted for V
the symbol for conductance is
g
what is conductance
the reciprocal of resistance
g=I/E
inside a typical resting cell, which of these is low in concentration: Cl, K, Na
Inside has low Na and Cl
what ion has high extracellular concentrations
Cl, Na
will ions pass through a phospholipid bilayer directly?
no, they must pass through a channel
as ions pass through the membrane what do they create?
they create concentration gradients
why are ions on one side of the phospholipid bilayer able to affect ions on the other side of the phospholipid bilayer?
because the membrane is thin - 5nm thick
when is the equilibrium potential reached?
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
what three things determine the rate of flow of an ion across a plasma membrane?
concentration gradient
voltage difference across the plasma membrane
conductance of ion channels
the membrane of potential where there is no net movement of a specific ion is called what
equilibrium potential of that ion (E_ion)
the equilibrium potential of an ion may be calculated by what
Nernst equation
what is the Nernst equation for any given ion?
E_ion = [ (RT) / (zF) ] * ln( [ion]_out / [ion]_in )
what do R, T, z, F mean in the Nernst equation?
R = gas constant T = absolute temperature z = valence of ion F = Faraday constant
what can we simplify about the Nernst equation at room temperature?
RT/F can be replaced by 58 mV
also natural logarithms (ln) is replaced by base 10 logarithms (log)
what is the difference between the Nernst equation at room temperature versus in a mammalian body?
instead of 58mV, it is instead 61mV
what is the Nernst equation only valid for?
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
what is the principle of electrical neutrality
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
Donnan equilibrium is
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
the Na/K pump is a(n) _______ (active/passive/facilited) pump
active, requires ATP
the Na/K pump pushes how many ions of Na/K in/out?
3 Na out
2 K in
why do we have both a Nernst equation and a Goldman equation?
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
what is the other name for the Goldman equation
constant-field equation
in a membrane’s resting state, the relative ionic permeabilities of K, Cl, and Na are?
P_K : P_Cl : P_Na = 1 : 0.45 : 0.02
using the Goldman equation and the permeabilities of K and Na, the membrane potential would be?
-71 mV
what are some passive membrane properties (3)?
transmembrane resistance
axial resistance
membrane capacitance
how is input resistance (r_in) defined?
r_ in = (delta V) / I
where delta V = change in membrane potential
I = injected current
specific membrane resistance of a unit area (R_m) has units of ?
ohms* cm ^2
specific membrane resistance (R_m) is a function of
density of ion channels and their conductance
how is the area of the size of a cell related to the resistance?
the larger the area, the smaller the resistance
what is the input resistance of an ideal spherical neuron?
R_in = R_m / (4pir^2) , where r is the radius of the cell
where does maximum membrane depolarization occur?
at the site of the current injection (or synapse)
what does r_i symbolize
it is the longitudinal resistance of intracellular fluid (axial resistance) for a unit length
what is lambda and how is it defined?
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
how would you determine the membrane voltage at any point on the membrane distant from the synaptic electronic depolarization?
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)
if x = lambda, what would be V_lambda?
0.37V_0
what happens to lambda when r_m gets bigger?
lambda also gets bigger
what does a larger lambda mean? how is a larger lambda significant?
larger lambda means less decay over the length
a larger lambda allows for a greater chance for two or more synaptic potentials to summate
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)
a synaptic potential would be expected to be larger in a smaller dendritic process
would you expect a larger lambda from a larger dendritic process or a smaller one?
you would expect a larger lambda from a larger dendritic process because they would have less r_in
what is tau
tau is defined as the time necessary for the electrotonic potential to decrement to 37% of its original peak value
what equation defines tau?
tau = r_m * C_m
where r_m = membrane resistance
C_m = membrane capacitance
how is the duration of tau determined?
V= V_max * e^(-t/tau)
what would you expect when t= tau?
V= 0.37V_max
if you have a larger tau, would you expect more or less decay over time?
larger tau -> less decay over time
