‘Gradients Across Membrane’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License. The dotted, blue channels represent sodium channels the striped, green channels represent potassium channels the solid yellow channels represent chloride channels. If the membrane is permeable to potassium, ions will flow outward.

If the membrane is permeable to sodium, ions will flow inward. The distribution of ions on either side of the membrane lead to electrochemical gradients for sodium and potassium that drive ion flow in different directions. For example, the electrochemical gradients will drive potassium out of the cell but will drive sodium into the cell. These concentration differences lead to varying degrees of electrochemical gradients in different directions depending on the ion in question. Ion Distribution Creates Electrochemical Gradients ‘Membrane at Rest’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License. The dotted, blue channels represent sodium leak channels the striped, green channels represent potassium leak channels the solid yellow channels represent chloride leak channels. This ion distribution leads to a negative resting membrane potential. For a typical neuron at rest, sodium, chloride, and calcium are concentrated outside the cell, whereas potassium and other anions are concentrated inside. ‘Membrane Potential’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License.Ī closer look shows that sodium, calcium, and chloride are concentrated outside of the cell membrane in the extracellular solution, whereas potassium and negatively-charged molecules like amino acids and proteins are concentrated inside in the intracellular solution. The inside of the neuron has a more negative charge than the outside of the neuron. This distribution of ions and other charged molecules leads to the inside of the cell having a more negative charge compared to the outside of the cell. Voltage DistributionĪt rest, ions are not equally distributed across the membrane. ‘Membrane Potential Terms’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License. An increase in membrane potential is a change that moves the cell’s membrane potential away from 0 or hyperpolarizes the membrane. A decrease in membrane potential is a change that moves the cell’s membrane potential toward 0 or depolarizes the membrane. This is also referred to as an increase in membrane potential. If the membrane potential moves away from zero, that is a hyperpolarization because the membrane is becoming more polarized. Since the membrane potential is the difference in electrical charge between the inside and outside of the cell, that difference decreases as the cell’s membrane potential moves toward 0 mV. This means that when a neuron’s membrane potential moves from rest, which is typically around -65 mV, toward 0 mV and becomes more positive, this is a decrease in membrane potential. This is also referred to as a decrease in membrane potential. If the membrane potential moves toward zero, that is a depolarization because the membrane is becoming less polarized, meaning there is a smaller difference between the charge on the inside of the cell compared to the outside. There is more than one way to describe a change in membrane potential. ‘Measuring Membrane Potential’ by Casey Henley is licensed under a Creative Commons Attribution Non-Commercial Share-Alike (CC BY-NC-SA) 4.0 International License. The membrane potential is the difference in voltage between these two regions. The membrane potential is measured using a reference electrode placed in the extracellular solution and a recording electrode placed in the cell soma. The recording electrode is inserted into the cell body of the neuron. A reference electrode is placed in the extracellular solution. The membrane potential is the difference in electrical charge between the inside and the outside of the neuron.

Electrical gradient