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Which one of the following events occurs first in a nerve impulse? a. Potassium ions move to the outside of a neuron. b. Sodium ions move to the inside of a neuron. c. Potassium ions move to the inside of a neuron. d. Sodium ions move to the outside of a neuron.

Theresa Perry

in Chemistry

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Jodi Brooks on June 6, 2018

The answer is b.Normally, the membranes of the neuronal cells have negative voltages across them (meaning that the inside is more negative relative to the outside). In the case of an action potential (when a neuron fires), the first thing that happens is that the membrane is depolarized, which means that the load of the inner part relative to the outside begins to reverse. This happens when the voltage-gated ion channels allow sodium ions (Na+, positively charged) to rush through the membrane and into the cell. Therefore, the polarity of the charge of the membrane begins to reverse (within the more positive, less positive), that is what we call the depolarization.


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