The action potential is caused by permeability changes in the plasma membrane.

True

Explanation:

During resting potential, the inside of the membrane is more negative compared to the outside. The activation gates of Na+ channels are closed and the membrane is impermeable for sodium ions. When a stimulus is strong enough to fire an action potential, change in the shape of the channel proteins opens the activation gates.  

Now, the gated Na+ channels are opened making the membrane more permeable for sodium ions.  The membrane is permeable for sodium ions for a brief period only when both activation and inactivation gates are open. This allows the entry of sodium ions inside the axon and makes is more positive.

1.the evidene of the reaction

2.yes

3.yes