Definition
- The resting membrane potential (RMP) is the electrical potential difference across the cell membrane at rest, with the inside negative relative to the outside.
- Neuron RMP−70 mV
- Skeletal & cardiac muscle RMP−90 mV
Normal Values
RMP and equilibrium potential of important ions (mammalian spinal motor neuron)
Ion
Na+
- ECF (mmol/L)
- 150
- ICF (mmol/L)
- 15
- Equilibrium potential
- +60 mV
K+
- ECF (mmol/L)
- 5.5
- ICF (mmol/L)
- 150
- Equilibrium potential
- −90 mV
Cl−
- ECF (mmol/L)
- 125
- ICF (mmol/L)
- 9
- Equilibrium potential
- −70 mV
HCO3−
- ECF (mmol/L)
- 21
- ICF (mmol/L)
- 5
- Equilibrium potential
- −25 mV
Ca++
- ECF (mmol/L)
- 2.5
- ICF (mmol/L)
- 10−4
- Equilibrium potential
- +130 mV
- K+ has the highest membrane permeability among the diffusible ions despite its larger atomic weight (39 vs 23 for Na+), because its effective hydrated radius is smaller.
- The membrane is practically impermeable to intracellular proteins and organic phosphates.