How do action potentials occur?

Action potentials are fundamental electrical impulses that neurons use to communicate. The process begins when a neuron's membrane potential depolarizes, meaning that the inside of the neuron becomes less negative compared to the outside. This depolarization occurs when the neuron receives sufficient stimulation, causing sodium channels to open and sodium ions to flow into the cell. If the depolarization reaches a certain threshold level, it triggers a rapid change in membrane potential, leading to the generation of an action potential.

This action potential is characterized by a sharp rise and subsequent fall in voltage across the neuron's membrane, allowing the electrical signal to propagate along the axon. This wave of depolarization moves down the axon, transmitting the signal to other neurons or target cells.

The other options provided do not accurately describe the process of action potential generation. Hyperpolarization refers to an increase in the negative charge inside the neuron, which is contrary to the initiation of an action potential. Losing the myelin sheath may affect the speed of signal propagation but does not initiate action potentials. The resting potential phase is characterized by stable, non-active conditions in the neuron and does not involve the changes in membrane potential needed to generate an action potential.