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The Resting Membrane Potential

(Sample Lesson)


Neurons, like other cells, are surrounded by a plasma membrane composed of a lipid bilayer that serves as both an insulator and a diffusion barrier to the movement of ions. Embedded in the lipid-bilayer are several types of protein channels and pumps that regulate the passage of ions across the membrane barrier.

Axon Membrane
Neuron axon membrane showing voltage gated channels and sodium-potassium pump

While neurons are at rest, two types of membrane proteins create and maintain a membrane potential of approximately -70 millivolt (mV).

  • Ion pump proteins use the energy stored in ATP (adenosine triphosphate) to pump Na+ out of the cell and K+ ions into the cell, creating opposing concentration gradients.
  • Leak channel proteins allow many of the K+ ions to passively move back out of the cell.

As positive ions accumulate outside the membrane, the inside of the membrane becomes relatively more negative (= less positive). Additionally, the cytoplasm along the inner surface of the membrane also contains a high concentration of negatively charged proteins.

The growing external positivity and internal negativity slow the outward leakage of K+ and the membrane comes to an equilibrium around -70 millivolts (mV), which is called the resting membrane potential.

Therefore, while the neuron is at rest, both electrical and chemical potentials are created. As long as the voltage-gated ion channels remain closed, the membrane stays at -70 mV. This is somewhat equivalent to pumping water uphill and storing it behind a dam while the floodgates remain closed.

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