During an action potential, the membrane becomes much more permeable to sodium ions than potassium ions, causing the membrane potential to become more positive, as sodium flows down its concentration gradient into the cell.

What is the purpose of the sodium-potassium pump? It maintains the concentration gradients of Na+ and K+, helping to stabilize resting membrane potential. If stopped working, electrochemical grandient would equalize/disappear and actions potentials could not be generated, so the cell would stop working.

The sodium pump is by itself electrogenic, three Na+ out for every two K+ that it imports. So if you block all sodium pump activity in a cell, you would see an immediate change in the membrane potential because you remove a hyperpolarizing current, in other words, the membrane potential becomes less negative.

Passive transport: membrane channels The sodium-potassium pump sets the membrane potential of the neuron by keeping the concentrations of Na+ and K+ at constant disequilibrium.

Therefore, potassium diffuses out of the cell at a much faster rate than sodium leaks in. Because more cations are leaving the cell than are entering, this causes the interior of the cell to be negatively charged relative to the outside of the cell.

In more detail: Sodium ions bind to the pump and a phosphate group from ATP attaches to the pump, causing it to change its shape. In this new shape, the pump releases the three sodium ions and now binds two potassium ions. Once the potassium ions are bound to the pump, the phosphate group detaches.

Sodium-Potassium Pump The pump undergoes a conformational change, translocating sodium across the membrane. The conformational change exposes two potassium binding sites on the extracellular surface of the pump. The phosphate group is released which causes the pump to return to its original conformation.

Terms in this set (6)

• First 3 sodium ions bind with the carrier protein.
• The cell then splits off a phosphate from ATP to supply energy to change shape of the protein.
• The new shape carries the sodium out.
• The carrier protein has the shape to bind with potassium.
• The phosphate is released and the protein changes shape again.

The typical cycle occurs in several steps. First, the pump binds ATP and three sodium ions from the cytoplasm. The ATP then phosphorylates the pump and it shifts in shape, creating an opening towards the outside of the cell. The sodium is released and two potassium ions are picked up.

Explanation: The sodium and potassium ions are pumped in opposite directions across the membrane. This pump build a chemical and electrical gradient. In nerve cells the pump is used to generate gradients of both sodium and potassium ions.