A neuron is at rest. A millisecond later, an action potential travels along its axon. What happened in the interim?

During the interim period between resting state and the propagation of an action potential, the neuron undergoes a sequence of events. Initially, the neuron is at its resting membrane potential, with a negative charge inside relative to the outside due to the distribution of ions across the cell membrane. Upon receiving a stimulus, typically from neurotransmitters released by neighboring neurons, ion channels in the neuron's membrane open, allowing an influx of positive ions (such as sodium ions) into the cell. This influx of ions depolarizes the membrane, creating a local potential called the graded potential. If the graded potential reaches a critical threshold, voltage-gated sodium channels along the axon membrane open, causing a rapid influx of sodium ions into the cell, further depolarizing the membrane and generating an action potential. Following the action potential, the neuron undergoes repolarization and hyperpolarization phases to restore its resting membrane potential. This involves the closing of sodium channels and the opening of potassium channels, allowing potassium ions to exit the cell, repolarizing the membrane. Sodium-potassium pumps then actively transport ions back to their resting concentrations, preparing the neuron for subsequent action potentials.