Neurons fire when there is a rapid flow of ions across the cell membrane, specifically the movement of Na+ and K+ ions. This movement occurs down their concentration gradient, which is spontaneous and does not require energy. Therefore, choice C is the correct option as it describes the movement of ions down their concentration gradient spontaneously.

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A Neuron Fires When

Question 56

Multiple Choice

A neuron fires when:

A) Na⁺ ions move against their concentration gradient spontaneously
B) Na⁺ ions are actively pumped down their concentration gradient
C) Na⁺ ions move down their concentration gradient spontaneously
D) Na⁺ ions are actively pumped against their concentration gradient

Correct Answer: