Measuring the Resting Membrane Potential

Author: Scott A. Sheffield MS

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In a resting axon, the distribution of cations and anions polarizes the plasma membrane. The intracellular fluid (ICF) becomes relatively negative to the extracellular fluid (ECF).

  • A image descriptionvoltmeter is used to measure the charge difference (voltage or electrical potential) between the ECF and ICF. The greater the difference, the greater the voltage.
An image showing how to measure the resting membrane potential using voltmeter with 2 electrods
An image showing how to measure the resting membrane potential using voltmeter (which is labeled) with 2 electrods
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An image showing how to measure the resting membrane potential using voltmeter (which is labeled) with 2 electrods
An image showing a ground electrod of voltmeter placed on the surface of a neuron cell membrane
An image showing a ground and recording electrods of voltmeter placed on the surface of a neuron cell membrane
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  • The recording electrode typically consists of a glass tube filled with KCl solution and a silver wire coated with Ag/AgCl. The electrode is able to convert ionic current to electrical current, which is sent to the voltmeter.
  • The ground electrode is image descriptionplaced outside the membrane and the recording electrode is inserted image descriptionrecording electrode into the axon.
  • Charge differences between the ECF and ICF (resting membrane potential or RMP) are image descriptiondisplayed in millivolts (mV) on the voltmeter.

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Factors That Determine the Resting Membrane Potential

  • The plasma membranes of resting axons are slightly polarized due to the unequal distribution of Na+, K+, Cl- and protein- ions in ECF and ICF.
  • Several factors play a role in creating the resting membrane potential.
  • image descriptionNa+/K+ pumps (or Na+/K+-ATPases) move Na+ and K+ ions to opposite sides of the membrane.
An image showing different types of channels in the (neuron) cell membrane (between ICF and ECF)
An image showing different types of channels (Na-K pump is labeled) in the (neuron) cell membrane (between ICF and ECF)
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  • Each pump protein uses one molecule of ATP to image descriptiontransfer 3 Na+ ions out of the cell and 2 K+ ions in.
  • As a result, Na+ ions are concentrated outside the axon membrane and K+ ions are concentrated inside. The unequal transfer of ions also contributes slightly to the polarity of the resting membrane.
  • Very few of the Na+ ions can diffuse back into the cell because most of the gated image descriptionNa+ channels are closed.
  • Most gated image descriptionK+ channels are also closed.
  • However, many image descriptionleak channels remain open, which increases the membrane’s permeability to K+ ions.
  • As K+ ions image descriptiondiffuse outward, the interior of the membrane becomes more negative and the exterior more positive, which significantly alters the RMP.

Use these interactive quizzes and labeling exercises to master nervous system anatomy.

An image showing different types of channels (Na-K pump is labeled) in the (neuron) cell membrane (between ICF and ECF)
An image showing different types of channels (Na channel - Na-K pump are labeled) in the (neuron) cell membrane (between ICF and ECF)
An image showing different types of channels (K channel - Na channel - Na-K pump are labeled) in the (neuron) cell membrane (between ICF and ECF)
An image showing different types of channels (K leak channel - K channel - Na channel - Na-K pump are labeled) in the (neuron) cell membrane (between ICF and ECF)
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  • Proteins- and other large anions confined within cell also contribute to the membrane’s polarity.
  • An image descriptionequilibrium is quickly reached be-tween the outward diffusion gradient for K+ and the inward electrical gradient.
An image showing different types of channels (K leak channel - K channel - Na channel - Na-K pump are labeled) in the (neuron) cell membrane (between ICF and ECF)
An image showing different types of channels equilibrium status of K leak channel in addition to (K channel - Na channel - Na-K pump are labeled) in the (neuron) cell membrane (between ICF and ECF)
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  • As the RMP stabilizes, Cl- ions passively disperse based on the permeability and polarity of the plasma membrane. Becasue the ICF is relatively negative, Cl- ions are repelled and tend to concentrate outside of the membrane.