The long structure leaving the cell body that action potentials travel along is called an axon.

Here's a breakdown:

* Cell body: The main part of a neuron containing the nucleus and other organelles.

* Axon: A long, slender projection that extends from the cell body. It's responsible for transmitting electrical signals (action potentials) away from the cell body to other neurons, muscles, or glands.

* Action potential: A brief electrical signal that travels down the axon.

Think of the axon as a long, thin wire that carries an electrical current. The action potential is like the current that flows through the wire.