Which ion sets the resting membrane potential in most neurons?

Which ion sets the resting membrane potential in most neurons?

• A. Sodium (Na+)
• B. Potassium (K+)
• C. Calcium (Ca2+)
• D. Chloride (Cl-)

Answer: (B)

The resting membrane potential is mainly set by how permeable the cell membrane is to different ions at rest. Neurons have many potassium leak channels, so the membrane is much more permeable to K+ than to the other ions. This makes the resting potential sit close to the potassium equilibrium potential, typically around -70 mV (often toward -90 mV if only K+ were considered). The Na+ gradient and channels are less influential at rest because the membrane is less permeable to Na+ then, so Na+ doesn’t pull the potential in as strongly. Calcium is kept at very low free intracellular levels and has limited resting permeability, so it contributes little to the baseline potential. Chloride’s influence varies by neuron and isn’t the universal determinant. The Na+/K+ ATPase helps maintain the ion gradients over time and adds a small hyperpolarizing influence, but the dominant factor shaping the resting membrane potential on a moment-to-moment basis is the high K+ permeability.

The resting membrane potential is mainly set by how permeable the cell membrane is to different ions at rest. Neurons have many potassium leak channels, so the membrane is much more permeable to K+ than to the other ions. This makes the resting potential sit close to the potassium equilibrium potential, typically around -70 mV (often toward -90 mV if only K+ were considered). The Na+ gradient and channels are less influential at rest because the membrane is less permeable to Na+ then, so Na+ doesn’t pull the potential in as strongly. Calcium is kept at very low free intracellular levels and has limited resting permeability, so it contributes little to the baseline potential. Chloride’s influence varies by neuron and isn’t the universal determinant.

The Na+/K+ ATPase helps maintain the ion gradients over time and adds a small hyperpolarizing influence, but the dominant factor shaping the resting membrane potential on a moment-to-moment basis is the high K+ permeability.