Since you left off the choices, I have to just present the facts of what occurs first in the nerve impusle. The first thing that will is happen is the sodium ios will move to the inside of the nueron. The second step is the potassium ions will move to the inside of the neuron. After those move into the nueron, calcium will then move into the nueron. Both the sodium and potassium have 1 postive charge. While the calcium ion has 2 positive charges.
