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The sodium-potassium pump is a protein pump found in the cell membrane of all animal cells.
Its main function is to transport sodium ions out of the cell and potassium ions into the
cell.
This serves a number of purposes, but is critically important to the function of neurons as it
helps to maintain a higher concentration of sodium ions outside the cell, and a higher
concentration of potassium ions inside the cell.
Preserving these differences in ion concentrations helps to stabilize the cell’s membrane potential.
This is critical for the neuron to be able to fire an action potential, which is the
basis of the electrical signaling of neurons.
The sodium-potassium pump is a large membrane-associated enzyme that uses the energy of adenosine triphosphate,
or ATP, to transport sodium and potassium ions across the cell membrane.
All of the details of how this is achieved are not yet fully clear, but the general process
involves the binding of ATP to the pump, which promotes the binding of 3 sodium ions and
the release of 2 previously bound potassium ions.
ATP is broken down and transfers a chemical group known as a phosphate group to the pump,
which prompts the pump to undergo a conformational change, or a change in its shape.
This causes the bound sodium ions to be released into the extracellular fluid.
At the same time, the pump binds 2 potassium ions, which also prompts another conformational
change that returns the pump to its previous configuration and the cycle begins again.
Each cycle of the pump causes 3 sodium ions to move out of the cell and 2 potassium ions
to move into the cell.
Because there is one more positive charge leaving the cell than entering, there is a
net loss of positive ions, which makes the resting membrane potential of the cell slightly
more negative.