When a neuron fires rushes into the axon and makes that part of the axon more charged compared to the extracellular fluid?

potassium ions, positively. a part of neuron transmission process referred to as action potential occurs during firing of neuron. during action potential, a region of the membrane allows potassium ions to enter into the axon and negatively charged chloride ions out of the cell. as a result, there is rapid increase in positive charge in neuron. when charge reaches threshold, that is a charge of +40mv an impulse is propagated down the fiber.