The Resting Membrane Potential

1
The Resting Membrane Potential

• Lecture 4

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Biolelectric Potential

• Communication within neuron
• electrical signal
• electric current movement of electrons
• Bioelectric movement of ions

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Ion Distribution

• Particles / molecules
• electrically charged
• Anions
• negatively charged
• Cations
• positively charged

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Ion Distribution

• Anions (-)
• Large intracellular proteins
• Chloride ions Cl-
• Cations ()
• Sodium Na
• Potassium K

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Resting Membrane Potential

• Na Cl-
• A- K

outside
Membrane
inside
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Membrane is polarized

• more negative particles in than out
• Bioelectric Potential
• like a battery
• Potential for ion movement
• current

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Resting Membrane Potential
outside











Membrane
-
-
-
-
-
-
-
-
-
-
-
inside
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Bioelectric Potential
OUTSIDE
INSIDE
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Forces That Move Ions
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Gradients

• Concentration (C)
• Electrostatic (E)

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Concentration gradient

• Movement of particles in fluid
• Move from area of high concentration to areas of
  low concentration
• Diffusion
• Random movement of particles

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Concentration gradient
Lo
HI
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Concentration gradient
Lo
HI
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Electrostatic gradient

• Ions charged particles
• Like charges repel
• Opposite charges attract

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Electrostatic gradient
like charges repel
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Electrostatic gradient
opposite
charges attract
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Equilibrium Potential

• Also called reversal potential
• Distribution of single ion across membrane
• e.g., EK, ENa, ECl-
• Potential for movement of ion if channel opens
• units millivolts (mV)
• outside 0, by convention

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Equilibrium Potential

• R gas constant
• F Faraday constant
• T temperature (K)
• Z valence (charge) of ion

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Equilibrium Potential

• Constants never change
• Assume 25 oC
• Use log10

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Equilibrium Potential
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Membrane Potential

• Net bioelectric potential
• for all ions
• Balance of both gradients
• concentration electrostatic
• Units millivolts (mV)
• Vm -65 Mv
• given by Goldman equation

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Membrane Potential Goldman Equation

• P permeability
• Net potential movement for all ions
• known VmCan predict direction of movement of any
  ion

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Organic anions - Membrane impermeable Opposing
electrical force not required

Vm -65 mV
A-
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Chloride ion
Cl-
Vm -65 mV

• Concentration gradient equal to electrostatic
  gradient.
• Leaks out neuron
• ECl- - 65 mV

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Potassium ion
Vm -65 mV
K

• Concentration gradient greater than electrostatic
  gradient.
• Leaks out neuron
• EK - 75 mV

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Na
Sodium ion
C
Vm -65 mV

• Concentration gradient and electrostatic gradient
  into neuron.
• ENa 55 mV

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Metabolic Pumps

• Active Transport mechanisms
• Require energy
• Move materials against gradient
• Na - K
• Calcium - Ca
• Nutrients, etc.

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Na - K Pump

• Maintains gradients at rest
• Pumps 3 Na out of cell
• 2 K into cell
• Energy ATP

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Inside
Outside
Na
Na
Na
K
K
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Inside
Outside
K
K
K
K