Final answer:
At rest, the activation gate of the fast Na+ channel is closed, and the inactivation gate is open. No Na+ can enter the cell until depolarization occurs, at which point the activation gate opens briefly before the inactivation gate closes to stop Na+ influx.
Step-by-step explanation:
Status of the Activation and Inactivation Gates of the Fast Na+ Channel at Rest
At rest, the voltage-gated Na+ channel has two gates: the activation gate and the inactivation gate. The activation gate is closed preventing Na+ from entering the cell, while the inactivation gate is open, which means it's ready to close shortly after the channel opens during an action potential. This arrangement ensures that Na+ influx will only occur when the cell depolarizes past a certain voltage threshold, typically around -55 mV. At that point, the activation gate opens rapidly, allowing Na+ to enter the cell and contribute to the rising phase of the action potential. Almost as quickly as it opens, the inactivation gate closes to terminate the Na+ influx even as the membrane potential is still depolarized. This sequence of gate operations is critical for the generation and propagation of action potentials in nerve and muscle tissues.
The resting state of the cell is also maintained by the Na+/K+ transporter, which actively pumps K+ ions into the cell and Na+ ions out, maintaining the established concentration gradients across the plasma membrane.