Final answer:
At the peak of an action potential, the activation gate of a voltage-gated Na+ channel is open, and the inactivation gate is closing, preventing further Na+ entry. Voltage-gated K+ channels open after a delay, allowing K+ to exit the cell which contributes to repolarization.
Step-by-step explanation:
At the peak of the action potential when the voltage reaches approximately +30 mV, the status of the activation gate and inactivation gate of a voltage-gated Na+ channel is as follows: the activation gate is open, which has allowed Na+ to rush into the cell, but as the membrane potential peaks, the inactivation gate starts closing. This closing of the inactivation gate prevents more Na+ from entering the cell, therefore contributing to the cessation of the depolarization phase. The voltage-gated K+ channels also respond to changes in membrane potential, with their gates opening at around -50 mV.
However, these K+ channels are slower to open and therefore, they open just as the voltage-gated Na+ channels are being inactivated. As positively charged K+ ions start to leave the cell, repolarization takes place. This event is crucial for resetting the membrane potential and preparing the cell for another potential action potential network should it be stimulated again.