A Neuron Fires When Na⁺ Ions

question 81

Multiple Choice

A neuron fires when Na⁺ ions

• A) move against their concentration gradient spontaneously.
• B) are actively pumped down their concentration gradient.
• C) move down their concentration gradient spontaneously.
• D) are actively pumped against their concentration gradient.
• E) None of the answer choices is correct.

---

Definitions:

Carbon Monoxide

A colorless, odorless, and toxic gas produced by incomplete combustion of carbon-containing materials, capable of binding with hemoglobin and reducing blood's oxygen-carrying capacity.

Water Vapor

The gaseous phase of water, present in the atmosphere and an important part of the Earth's water cycle and weather.

Carbon Dioxide

A colorless, odorless gas produced by burning carbon and organic compounds and by respiration. It is naturally present in air and is absorbed by plants in photosynthesis.

Simple Organic Molecules

Basic compounds containing carbon that are the building blocks of more complex organic molecules.