In the Action at the Synapse activity, you will learn all about what goes on at the synapse, including the effects of neurotransmitters and drugs. These represent communication between neurons. But what about the communication within a neuron — the change in electrical charge that causes a neuron to fire an excitatory or inhibitory message into the synapse? This neural impulse is called the action potential, and it is shown by the dot of light in the animation above. Here you see one neuron's action potential traveling from the dendrites to the axon terminals, where it triggers an action potential in the adjacent neuron's dendrites. Just how is this electrical message being transmitted? What causes a neuron to "fire"? What is the "all-or-none law" all about?
