In a neuron, what creates the electrochemical gradient favoring the outflow of K⁺ when the cell is at rest?
a. Na⁺/K⁺-ATPase
b. Voltage-gated K⁺ channels
c. Voltage-gated Na⁺ channels
d. Ligand-gated Na⁺/K⁺ channels

Verified step by step guidance

1. Understand the concept of electrochemical gradient: It is the combination of electrical and chemical gradients that influence the movement of ions across a membrane.
2. Identify the role of Na+/K+-ATPase: This enzyme actively transports 3 Na+ ions out of the neuron and 2 K+ ions into the neuron, using ATP. This creates a concentration gradient with more Na+ outside and more K+ inside the cell.
3. Recognize the resting membrane potential: At rest, the inside of the neuron is negatively charged relative to the outside, primarily due to the activity of Na+/K+-ATPase and the presence of negatively charged proteins inside the cell.
4. Consider the movement of K+ ions: The concentration gradient created by Na+/K+-ATPase favors the outflow of K+ ions, as there is a higher concentration of K+ inside the cell compared to outside.
5. Evaluate the options: Na+/K+-ATPase is responsible for maintaining the concentration gradient that favors the outflow of K+ when the neuron is at rest, making it the correct answer.

Key Concepts

Electrochemical Gradient

An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. It consists of two parts: the electrical potential and a difference in the chemical concentration across a membrane. In neurons, this gradient is crucial for the movement of ions like K+ and Na+, influencing the cell's resting membrane potential.

Na+/K+-ATPase Pump

The Na+/K+-ATPase pump is an essential membrane protein that uses ATP to transport three Na+ ions out of the cell and two K+ ions into the cell. This active transport mechanism helps maintain the resting membrane potential by creating a high concentration of K+ inside the cell and a high concentration of Na+ outside, contributing to the electrochemical gradient.

Resting Membrane Potential

The resting membrane potential is the voltage difference across the neuronal membrane when the cell is not transmitting a signal. It is typically around -70 mV in neurons, primarily due to the differential distribution of ions, especially K+ and Na+, across the membrane, maintained by the Na+/K+-ATPase pump and selective permeability to K+.