Question

Resting membrane potential depends on A. the differential distribution of ions across the axon membrane. B. active transport. C. selective permeability. D. All of the above

Short answer

D. All of the above

Step-by-step solution

Understanding Resting Membrane Potential

Resting membrane potential is the electrical potential difference across the cell membrane when the cell is in a non-excited state.

Importance of Ion Distribution

The resting membrane potential depends on the distribution of ions like Na+, K+, and Cl- across the axon membrane. These ions have different concentrations inside and outside the cell, creating an electrical gradient (Option A).

Role of Active Transport

Active transport mechanisms like the sodium-potassium pump (Na+/K+ ATPase) help maintain these ion gradients by pumping Na+ out of the cell and K+ into the cell against their concentration gradients (Option B).

Selective Permeability of the Membrane

The axon membrane's selective permeability to different ions contributes to the resting membrane potential. This selective permeability is essential because it allows certain ions to move more freely than others (Option C).

Conclusion

Since all of these factors – differential distribution of ions, active transport, and selective permeability – are crucial for maintaining the resting membrane potential, the correct answer is 'All of the above' (Option D).

Key concepts

Ion Distribution

In a neuron, resting membrane potential is largely determined by the distribution of ions between the inside and outside of the cell. Neurons have different concentrations of various ions, such as sodium (Na+), potassium (K+), and chloride (Cl-). These ions have specific roles:

• Sodium (Na+): Predominantly found outside the cell.
• Potassium (K+): Mostly present inside the cell.
• Chloride (Cl-): More abundant outside the cell.

This unequal distribution creates an electrical gradient, also known as the membrane potential. The difference in ion concentration across the membrane is essential for generating and maintaining the resting membrane potential. It acts as a sort of “battery” that is ready to power the cell's activities. Without this gradient, the neuron would not be able to function properly.

Active Transport

To maintain the ion gradients necessary for the resting membrane potential, cells use active transport mechanisms. A key player here is the sodium-potassium pump (Na+/K+ ATPase). This pump uses energy from ATP to move ions against their concentration gradients:

• Sodium (Na+): Pumps 3 Na+ ions out of the cell.
• Potassium (K+): Pumps 2 K+ ions into the cell.

This active transport is crucial because it restores and maintains the high concentration of K+ inside the cell and the high concentration of Na+ outside the cell. By doing so, it helps to keep the resting membrane potential stable. Without active transport, the ionic gradients would dissipate, and the cell would lose its ability to generate electrical signals.

Selective Permeability

Selective permeability refers to the ability of the cell membrane to allow certain ions to pass through while blocking others. This is achieved through specific ion channels. Key points include:

• Potassium Channels: Highly permeable to K+, allowing it to move freely.
• Sodium Channels: Less permeable to Na+, limiting its movement.

This selectivity is crucial for maintaining the resting membrane potential. The high permeability to K+ allows it to leave the cell, making the inside more negative. This imbalance is what primarily contributes to the resting membrane potential. Selective permeability is therefore a fundamental property of the cellular membrane that ensures proper cell function.