what occurs during depolarization of an axon

June 28, 2026

During depolarization of an axon, voltage-gated sodium (Na⁺) channels open and Na⁺ rushes into the neuron, making the inside of the membrane much less negative (and briefly positive) compared with the outside.

Quick Scoop: What Occurs During Depolarization of an Axon?

Think of an axon like a resting battery that suddenly gets switched “on.” Depolarization is that switch moment when the electrical state of the membrane flips.

1. Starting point: Resting state

The axon starts at its resting membrane potential, around −70 mV (inside negative compared to outside).

At rest, there is more Na⁺ outside the neuron and more K⁺ inside, maintained by leak channels and the sodium–potassium pump.

2. Hitting threshold

A stimulus (from another neuron or a receptor) causes a small local depolarization, making the inside slightly less negative.

If this change reaches a threshold level (often around −55 mV), voltage-gated Na⁺ channels at the axon hillock rapidly open.

3. Sodium rushes in (the core of depolarization)

Once Na⁺ channels open, Na⁺ floods into the axon down both its concentration gradient and electrical gradient.

This rapid influx of positive charge makes the membrane potential shoot upward toward zero and then into positive values (for example, around +30 mV).

Opening of some Na⁺ channels triggers more to open (a positive feedback loop), giving the all‑or‑none action potential.

4. Inside becomes positive

During peak depolarization, the inside of the axon is now positive relative to the outside, which is the reverse of the resting condition.

This change in charge distribution at one segment of membrane helps depolarize the next segment along the axon, so the action potential travels down the nerve.

5. Transition to repolarization

At the peak of depolarization, Na⁺ channels inactivate (their inactivation gates close), so Na⁺ can no longer enter.

Voltage-gated K⁺ channels open, K⁺ flows out, and the membrane potential starts to fall back down—this is repolarization and comes right after depolarization.

Key facts in bullet form

Resting: inside negative, outside positive (about −70 mV).

Depolarization trigger: threshold reached → voltage-gated Na⁺ channels open.

Main event: Na⁺ rushes into the axon, making the inside less negative and then positive.

Result: membrane potential rapidly rises (the “upstroke” of the action potential).

Aftermath: Na⁺ channels inactivate, K⁺ channels open, leading into repolarization.

Simple one‑sentence answer for exams

During depolarization of an axon, voltage‑gated sodium channels open and Na⁺ ions rush into the neuron, causing the membrane potential to become less negative and briefly positive inside relative to outside.

Information gathered from public forums or data available on the internet and portrayed here.