Question

Which of the following contribute(s) to the resting membrane potential? the relative leakiness of the membrane to \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{+}\) b. active transport of ions across the membrane c. concentration of \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{+}\) inside and outside of the cell d. all of the above e. b and c only

Short answer

The correct answer is 'd. all of the above'. All mentioned factors - the relative leakiness of the membrane to \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{+}\), active transport of ions across the membrane, and the concentration of \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{+}\) inside and outside of the cell - contribute to the resting membrane potential.

Step-by-step solution

Understand the Nature of the Problem

The exercise asks which of the given options contributes to the resting membrane potential. The resting membrane potential is a balance of electrical charges across the cell membrane when the cell is at 'resting' or not actively sending signals. It is primarily established by the differential distribution of sodium (\(\mathrm{Na}^{+}\)) and potassium (\(\mathrm{K}^{+}\)) ions across the cell membrane, and determined by ion channels and ion transport proteins.

Evaluate Each Option

We now evaluate each option according to our understanding of the cell membrane and resting potential. \n\na. The relative leakiness of the membrane to \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{+}\): This is true. The cell membrane has different permeabilities for different ions, and the leakiness of the membrane to these ions contributes to the resting potential.\n\nb. Active transport of ions across the membrane: Also true. The sodium-potassium pump (an example of active transport) maintains the concentration gradients of \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{+}\) across the membrane, thus contributing significantly to the resting potential.\n\nc. Concentration of \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{+}\) inside and outside of the cell: This too is true. The differential concentration of these ions inside and outside the cell creates an electric potential difference, also contributing to the resting potential.

Select the Correct Answer

Since all options (a, b, and c) are correct, the correct answer to the exercise would be 'd. all of the above'.

Key concepts

Sodium-Potassium Pump

The sodium-potassium pump is a crucial protein found in the cell membrane. It actively transports ions using energy from ATP. This pump moves sodium (\(\text{Na}^+\)) ions out of the cell and potassium (\(\text{K}^+\)) ions into the cell. In each cycle, it typically exchanges three sodium ions for two potassium ions. This unequal exchange helps maintain a higher concentration of sodium ions outside the cell and a higher concentration of potassium ions inside.
This action is essential for maintaining the resting membrane potential of cells, which is a critical aspect of nerve impulse transmission and muscle contraction.
The pump's activity is a classic example of active transport, meaning it requires energy to function. By constantly working, it sustains the ion concentration gradients that are vital for the resting potential.

Ion Channels

Ion channels are specialized proteins embedded in the cell membrane that allow specific ions to pass through. They provide a pathway for ions to enter or leave a cell, driven by their concentration gradients. There are different types of ion channels, including voltage-gated, ligand-gated, and leak channels.
Leak channels are particularly important for maintaining the resting membrane potential because they allow potassium ions to move more freely than sodium ions. This selective permeability helps establish the overall negative charge inside the cell compared to the outside.
Ion channels can open or close in response to various signals, thus regulating the flow of ions across the cell membrane. Their function is vital for processes such as neural signaling and muscle contraction.

Membrane Permeability

Membrane permeability refers to the ability of the cell membrane to allow particular ions and molecules to pass through it. This property is essential for maintaining the cell's internal environment. It is primarily influenced by the types and numbers of ion channels present in the membrane.
In the context of resting membrane potential, the permeability of the membrane to potassium and sodium ions is of particular importance. Potassium leak channels contribute to a higher permeability of the membrane to potassium ions compared to sodium ions.
This differential permeability is a key factor in establishing the resting membrane potential. Changes in membrane permeability can significantly affect cellular functions, such as the initiation of action potentials in neurons.

Ion Concentration Gradient

Ion concentration gradients refer to the differences in ion concentration across the cell membrane. These gradients are crucial for many cellular processes, including the maintenance of the resting membrane potential.
Sodium and potassium ions have very different concentrations inside and outside of cells, with sodium being more prevalent outside and potassium more abundant inside the cell.
The sodium-potassium pump plays a significant role in maintaining these gradients, continuously operating to correct any deviations.
The stored energy in these gradients is used by the cell to perform work, such as propagating nerve signals. Maintaining these gradients is a constant, energy-consuming process for the cell, highlighting their importance.

Active Transport

Active transport is the process of moving molecules across the cell membrane against their concentration gradient, utilizing energy. The sodium-potassium pump is a prime example of active transport.
This mechanism is crucial for maintaining concentration gradients of ions, such as sodium and potassium, across the cell membrane.
Unlike passive transport, which relies on diffusion, active transport requires cellular energy in the form of ATP. This energy is used to move ions from areas of lower concentration to areas of higher concentration, thus maintaining the necessary gradients for the resting membrane potential.
Active transport processes are vital for a range of physiological functions, such as nutrient uptake, waste removal, and electrical signal transmission in nerve and muscle cells.