Why are nerve impulses called "action potentials"?

Question

(why don't they just call them nerve impulses?)

Answer 1

Because they can potentially cause an action! They can either cause a movement (action) or a feeling.

Answer 2

The Resting Potential:

The cell membrane is negative just inside the cell. The cell is said to be polarized. The membrane stores energy by holding these opposite charges apart. Positive outside and negative inside. The voltage across the membrane is called the membrane potential. This is the membrane's potential to do work. If the cell is not doing work it is called the resting potential. (-70 millivolts). When the cell is stimulated the voltage across its membrane changes and it becomes an excitable cell.

The plasma membrane of the neuron contain many sodium-potassium pumps. These pumps are ATP driven and collect sodium on the outside of the cell and potassium on the inside of the cell. Potassium and sodium may diffuse sparingly through the membrane, but the undisturbed cell can maintain the steep gradients with these pumps.

A change in the resting potential can affect its permeability. This is called a stimulus. If this stimulus causes a decrease from the resting potential of -70 millivolts in the direction of 0, the membrane is said to be depolarized. This creates an Action Potential.

The action potential is an all or none event. A neuron has a threshold potential -50 millivolts, this must be attained before the sodium gates open and allow the sodium to pour into the cell.