When a neuron becomes excited and is activated, the permeability of the cell membrane increases temporarily, meaning that ions can cross through more easily. because there is more sodium outside, sodium rushes inside the cell during this increased permeability. when this happens, that section of the neuron becomes depolarized because it is not as polarized as it was before (where there was a lot more positive charge outside before, now there is less so). if the stimulus is great enough, this local depolarization will cause an action potential or nerve impulse; basically the nerve will "fire."almost immediately after a depolarization, the membrane permeability changes again. this time, potassium is able to cross the membrane and potassium ions rush out of the cell, restoring the neuron’s normal resting state of depolarization. later, an active sodium-potassium pump will pump both types of ions back to their original position to essentially reset the neuron. the action potential travels along the neuron until it reaches the axon terminal, which dead-ends into the synapse (the gap before the next neuron). this causes neurotransmitters to release intothe synapse and bind on the dendrites of the next neuron. if there is enough of the neurotransmitter released, the next neuron will depolarize and fire.