The correct option is - (a) the activation and inactivation gates must both be open.
Explanation:
Option (a) is correct because of the following reason -
The axonal membrane is at its natural resting potential until an action potential occurs, and channels are deactivated and blocked on the extracellular side by their activation gates. The activation gates open in response to an electric current, allowing positively charged ions to flow into the neuron through the channels. When enough has penetrated the neuron and the membrane potential has reached a certain level, the channels inactivate themselves by closing their inactivation gates at the height of the action potential. The inactivation gate can be thought of as a "plug" tethered to the intracellular alpha subunit's domains III and IV. When the inactivation gate is closed, the flow of through the channel is stopped. As a result, both the activation and inactivation gates must be open to enable sodium ions to enter the cell.
