Final answer:
The initial influx of Na+ ions during an action potential triggers a positive feedback loop, causing further depolarization and the propagation of the action potential. Potassium channels and the sodium/potassium pump play roles in repolarization and restoring resting potential, but are not part of this initial positive feedback mechanism.
Step-by-step explanation:
In the first phase of triggering an action potential in a neuron, Na+ ions flow in and trigger a positive feedback loop. Voltage-gated sodium channels open in response to the initial entry of sodium into the cell, which in turn allows more sodium to enter the cell. As more Na+ ions enter the neuron, the internal voltage of the neuron further increases, causing even more sodium channels to open at further distances from the cell body. This positive feedback loop leads to a rapid increase in the neuron's internal voltage, resulting in depolarization and the propagation of the action potential along the axon.
After the peak depolarization is reached, a negative feedback loop takes over to return the neuron to its resting state. This involves the inactivation of sodium channels and the opening of potassium ion channels, allowing K+ ions to flow out of the cell, initiating repolarization. The sodium/potassium pump then actively restores the resting potential by moving Na+ out and K+ into the cell, but this process occurs after the action potential, not during the initial positive feedback loop phase.