Question

In a neuron, what creates the electrochemical gradient favoring the outflow of \(\mathrm{K}^{+}\) when the cell is at rest? a. \(\mathrm{Na}^{+} / \mathrm{K}^{+}\) -ATPase b. voltage-gated \(\mathrm{K}^{+}\) channels c. voltage-gated Na \(^{+}\) channels d. ligand-gated \(\mathrm{Na}^{+} / \mathrm{K}^{+}\) channels

Short answer

The electrochemical gradient favoring the outflow of \(\mathrm{K}^{+}\) when a neuron is at rest is primarily created by the \(\mathrm{Na}^{+} / \mathrm{K}^{+}\)-ATPase, making option a the correct answer.

Step-by-step solution

Understand the resting membrane potential and ion movement

The resting membrane potential of a neuron is a result of the concentration gradient of different ions, primarily \(\mathrm{K}^{+}\), \(\mathrm{Na}^{+}\), and \(\mathrm{Cl}^{-}\). When the neuron is at rest, the \(\mathrm{K}^{+}\) ions move out of the cell more easily than \(\mathrm{Na}^{+}\) ions can move in, which leads to a negative charge inside the cell. The main factors creating this gradient include ion channels and ion pumps.

Analyze option a: \(\mathrm{Na}^{+} / \mathrm{K}^{+}\)-ATPase

The \(\mathrm{Na}^{+}/\mathrm{K}^{+}\)-ATPase is an active transport pump that moves \(\mathrm{K}^{+}\) ions into the cell and \(\mathrm{Na}^{+}\) ions out of the cell. This pump helps maintain the resting membrane potential by maintaining the concentration gradient of \(\mathrm{K}^{+}\), allowing it to move out of the cell more easily than \(\mathrm{Na}^{+}\) ions can move in. This makes it a candidate for the answer.

Analyze option b: voltage-gated \(\mathrm{K}^{+}\) channels

Voltage-gated \(\mathrm{K}^{+}\) channels open in response to changes in the membrane potential. While these channels are involved in the repolarization phase of action potentials, they do not play a significant role in maintaining the resting membrane potential.

Analyze option c: voltage-gated Na \(^{+}\) channels

Voltage-gated Na \(^{+}\) channels open in response to changes in the membrane potential, which allows Na \(^{+}\) ions to flow into the cell. These channels are involved in the depolarization phase of action potentials, but they are closed when the neuron is at rest and do not contribute to the resting membrane potential.

Analyze option d: ligand-gated \(\mathrm{Na}^{+} / \mathrm{K}^{+}\) channels

Ligand-gated \(\mathrm{Na}^{+}/\mathrm{K}^{+}\) channels open in response to binding of specific signaling molecules, such as neurotransmitters. These channels play a role in synaptic communication between neurons but do not have a primary role in maintaining the resting membrane potential.

Determine the correct answer

Based on the analysis of the given options, we can conclude that the electrochemical gradient favoring the outflow of \(\mathrm{K}^{+}\) when the cell is at rest is primarily created by the \(\mathrm{Na}^{+} / \mathrm{K}^{+}\)-ATPase, making option a the correct answer.

Key concepts

Electrochemical Gradient

An electrochemical gradient is a crucial concept in understanding how ions move across cell membranes. It comprises two components: the concentration gradient and the electric gradient. - **Concentration Gradient**: This refers to the difference in ion concentration inside and outside the cell. For instance, neurons maintain a higher concentration of potassium ions (\(K^{+} \)) inside the cell compared to outside.- **Electric Gradient**: This is about the charge difference across the cell membrane. Since potassium ions are positively charged, their movement is influenced by the cell's electrical charge.Together, these gradients create the forces that drive ions in or out of the cell. The electrochemical gradient is essential for the resting membrane potential, which keeps the interior of the cell negatively charged compared to the outside.

Na+/K+-ATPase

The sodium-potassium pump, or \( \text{Na}/\text{K-ATPase} \), is a key player in maintaining the cell's electrochemical gradient. This pump is a type of ion pump that actively transports ions across the cell membrane. Here's how it works:- It **pumps out three \( \text{Na}^{+} \) ions** from the cell.- Simultaneously, it **pumps in two \( \text{K}^{+} \) ions** into the cell.This action is critical because it keeps the intracellular \( \text{K}^{+} \) concentration high and the \( \text{Na}^{+} \) concentration low. The pump requires energy, derived from ATP, to facilitate this ion movement against their concentration gradients. Its action contributes significantly to the resting membrane potential, as it generates a net negative charge inside the cell.

Voltage-Gated Channels

Voltage-gated channels are membrane proteins that open or close in response to changes in the membrane's electric potential. These channels play a crucial role during the action potential but are less involved when the cell is at rest.- **Voltage-Gated \( \text{K}^{+} \) Channels**: These channels open mainly during the repolarization phase of the action potential, allowing \( \text{K}^{+} \) to exit the neuron, thereby returning the membrane potential back to a negative value.- **Voltage-Gated \( \text{Na}^{+} \) Channels**: These are responsible for the depolarization phase, during which the membrane potential becomes more positive as \( \text{Na}^{+} \) floods into the cell.While these channels are vital for the rapid signaling changes in neurons, they remain closed at rest and don't actively contribute to maintaining the resting membrane potential, unlike passive leak channels or the \( \text{Na}/\text{K-ATPase} \) pump.

Ion Pumps

Ion pumps are integral membrane proteins that use energy to move ions across the biological membrane, typically against their concentration gradient.- **Role in Resting Potential**: Ion pumps, such as the \( \text{Na}/\text{K-ATPase} \), are vital in establishing the resting membrane potential by maintaining the essential ion gradients.- **Energy Requirement**: Unlike ion channels, these pumps require energy, which they get from ATP, to transport ions.- **Types and Functionality**: While the sodium-potassium pump is the most recognized, cells have various other ion pumps that contribute to maintaining homeostasis and ion balance.Ion pumps are indispensable for proper cellular function, not just in neurons but across all cell types, as they help maintain the necessary conditions for cell survival and signal transmission.