The order of events when a neuron fires an action potential is as follows:
1. Depolarization: The neuron's membrane potential is changed from its resting potential to a more positive voltage.
2. Threshold: The membrane potential reaches a critical level, known as the threshold potential, which triggers the action potential.
3. Action potential: An all-or-none electrical impulse is generated and propagates along the axon.
4. Repolarization: The membrane potential returns to its resting potential.