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All right.
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When we're talking about nerve signals, we're actually talking about specifically they're called action potentials.
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And so this question is asking about the beginning of an action potential, which is a process called depolarization.
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And what happens is this is going to represent a nerve cell.
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This is the inside of it.
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And so this nerve cell has a charge of about negative 70 milliseconds.
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And so in order for an action potential to start, this voltage has to change.
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And the way that that happens is concentrated on the outside is our sodium ions represented by na plus.
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And so when a signal begins and initiates an action potential, sodium will rush into the cell because it's got a higher concentration outside of the cell, and so it'll want to go inside.
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And it will actually cause this negative 70 to move towards zero...