November 29, 2020
Biol 4102 / 6102: Fundamentals of Neurobiology
Electrical Signaling, Membrane Potential
Chapter 3
Membrane Potential
oBasis of cellular signaling
Action Potential
Synaptic Potential
Terminology
oCharge: positive or negative and carried by ions
units: Coulombs
oVoltage (Potential): a measure of how much charge is separated
units: Volts (V)
oCurrent (I): the flow of positive charge
units: Amperes (A)
oPermeability: the relative ease with which ions can flow through channels
oConductance (G): a measure of the ease with which charge can flow
units: Siemens (S)
inverse of Resistance (R), units: Ohms ()
Method for recording Neuronal Membrane Potential
oVoltage Recording with intracellular microelectrodes
records the potential difference across the membrane
Physical basis for membrane potential
oSeparation of charge by the membrane
oDifferential concentrations of ions across membrane
Na/K pump maintains distribution
oSelective Permeability to Na+, K+, Cl- ions
Resting conductance: Based on ion channels
Nernst Equilibrium Potential
o[This is very important!!!] The Equilibrium potential for an ion is the potential at which
there is no net movement of an ion due to a balance between electrical and chemical
gradients
E
x
= * ln [X]
o
[X]
i
RT
ZF
E
x
= * ln [X]
o
[X]
i
[X]
o
[X]
i
RT
ZF
oWhere:
Ex= Equilibrium Potential for ion X
[X]o is the concentration of ion X outside the neuron
[X]i is the concentration of ion X inside the neuron
R= Universal gas constant
T= Temperature in Kelvin
Z= Valence
F= Faraday constant
Simplified Nernst Equation: At 37° C, RT/F=26.7mV. The conversion of natural logarithm
to base 10 logarithm is 2.3
Ex= * log [X]o
[X]i
62
z
Ex= * logEx= * log [X]o
[X]i
[X]o
[X]i
62
z
Ex= * log
Glial cells are very permeable to K+ but not permeable to other ions. Therefore glial
membrane potential is the same as EK.
p. 1
