Final answer:
Ion channel inactivation refers to the temporary closure of an ion channel's inactivation gate after initial activation, preventing the channel from reopening in response to a continuing stimulus.
Step-by-step explanation:
Ion channel inactivation is the process by which a voltage-gated ion channel closes and becomes temporarily unable to reopen in response to a stimulus, even if that stimulus continues. This process occurs after the activation of the ion channel and is characterized by a distinct inactivation gate that closes after the channel opens in response to a change in membrane voltage. During depolarization of an action potential, voltage-gated Na+ channels open when the membrane potential becomes less negative, reaching the threshold of around -55mV.
These channels have two gates: the activation gate and the inactivation gate. Once the threshold is reached, the activation gate allows Na+ ions to rush into the cell, leading to a peak in depolarization. Subsequently, during this peak, the inactivation gate closes, preventing further Na+ ions from entering, thus contributing to the repolarization of the neuron. When repolarization occurs, the membrane potential becomes more negative again, and eventually, the inactivation gate re-opens, preparing the channel for another round of potential action.
To answer the student's question directly, ion channel inactivation refers to option 2) Closing of the channel even when the stimulus continues.