1. What is a membrane potential? How is a resting membrane potential established? Include the following key terms: Na+ ions, K+ ions, Na+ channels, K+ channels, Na+/K+ pumps, concentration gradients, membrane permeability, leak channels.

Answer 1

A membrane potential refers to the difference in electric charge across a cellular membrane, which is essential for various physiological processes, including nerve impulse transmission and muscle contraction. The resting membrane potential is the electrical potential difference across the membrane of a resting neuron, typically around -70 mV.

The establishment of the resting membrane potential involves several key components and processes:

1. Concentration Gradients: There are differences in the concentrations of specific ions, primarily sodium (Na+) and potassium (K+) ions, inside and outside the cell. Typically, there is a higher concentration of Na+ ions outside the cell and a higher concentration of K+ ions inside the cell. These gradients create a driving force for the movement of these ions across the membrane.

2. Membrane Permeability: The cell membrane is selectively permeable, allowing certain ions to move more freely than others. At rest, the membrane is more permeable to K+ ions than to Na+ ions, largely due to the presence of leak channels that allow K+ ions to flow out of the cell while fewer Na+ ions leak into the cell.

3. Ion Channels: Na+ channels and K+ channels are integral membrane proteins that facilitate the flow of these ions across the membrane. While Na+ channels are generally closed during the resting state, K+ channels (specifically K+ leak channels) are open, allowing K+ ions to move out of the cell, which contributes to the negative charge inside the cell.

4. Na+/K+ Pumps: The Na+/K+ pump is an active transport mechanism that helps maintain the concentration gradients of Na+ and K+ ions. For every three Na+ ions that are pumped out of the cell, two K+ ions are pumped into the cell. This process requires energy in the form of ATP, helping to counterbalance the leakage of ions and maintain the resting membrane potential.

In summary, the resting membrane potential is primarily established by the differential concentration gradients of Na+ and K+ ions, the cell's selective permeability to these ions, the activity of leak channels, and the action of the Na+/K+ pump, all of which combine to create a polarized membrane with a negative internal charge relative to the outside.