What ion(s) must the membrane become permeable to for a nerve impulse to pass through a nerve fiber?

For a nerve impulse to pass through a nerve fiber, the membrane of the neuron must become permeable to specific ions. Specifically, the membrane becomes permeable to sodium ions (Na+) and potassium ions (K+).

When a neuron is at rest, the membrane is more permeable to potassium ions than to sodium ions. This creates an electrical gradient across the membrane, with a negative charge inside the neuron and a positive charge outside.

When a neuron is stimulated, channels in the membrane open to allow sodium ions to flow into the neuron, causing a depolarization of the membrane. If the depolarization reaches a certain threshold, voltage-gated sodium channels open, allowing a rapid influx of sodium ions and the propagation of an action potential along the nerve fiber.