why does a neuron fire?

Answer 1

A neuron fires during a process called depolarization. Normally, something called a sodium potassium pump keeps a positive charge outside of the cell and a negative charge inside the cell. When a nerve wants to fire, sodium gates open and flood the cell giving the cell a positive charge. This happens several times down the length of the neuron. If this impulse is then passed onto another cell, it too will fire. It is an all or none process, if a nerve cell recieves more excitatory impulses than inhibitory impulses it will fire. Does this answer your question?

Answer 2

Because he's had all he's gonna take from that freakin proton, the bastard.