The central nervous system is constantly sending electronic impulses called action potentials which are propagated along nerve cells via the finely-tuned actions of various proteins that are located in the nerve cell’s membrane. First, there is a membrane protein that simultaneously pumps potassium ions into the cell and sodium ions out of the cell. This sets up a chemical gradient across the membrane. There is more potassium inside the cell than outside, and there is more sodium outside than inside. Also, there are more negatively charged ions inside the cell so there is a voltage drop (50-100 millivolt) across the membrane. In addition to the sodium-potassium pump, there are also sodium channels and potassium channels. These membrane proteins allow sodium and potassium, respectively, to pass through the membrane. They are normally closed, but when the action potential travels along the nerve cell tail, it causes the voltage-controlled sodium channels to open quickly. Sodium ions outside the cell then come streaming into the cell down the electro-chemical gradient. As a result the voltage drop is reversed and the decaying electronic impulse, which caused the sodium channels to open, is boosted as it continues on its way along the nerve cell tail. When the voltage goes from negative to positive inside the cell, the sodium channels slowly close and the potassium channels open. Hence the sodium channels are open only momentarily, and now with the potassium channels open, the potassium ions concentrated inside the cell come streaming out down their electro-chemical gradient. As a result the original voltage drop is reestablished. This process repeats itself until the impulse finally reaches the end of the nerve cell tail. Read more