How Stress Affects Your Brain: Understanding the HPA Axis and Nervous System

stresssomatics

Aug 4

Have you ever felt like your body is stuck in “on” mode—even when there’s nothing wrong?

That’s not just in your head. It’s your stress response system, and two powerful players are at work: your HPA axis and your autonomic nervous system (ANS).

Let’s break it down in simple terms.

What Is the HPA Axis?

The HPA axis (hypothalamic-pituitary-adrenal axis) is your body’s longer-term stress response system. When you feel unsafe, overwhelmed, or threatened—your brain sends signals that release cortisol, your main stress hormone.

Cortisol helps you stay alert and energized in short bursts. But when your stress becomes chronic, the HPA axis can stay stuck in overdrive—leading to exhaustion, sleep problems, mood swings, and even burnout.

What About the Nervous System?

Your autonomic nervous system (ANS) works even faster than the HPA axis. It instantly scans for danger and decides:

Should I fight or flee? (Sympathetic)
Should I shut down or numb out? (Dorsal vagal)
Or can I stay calm, connected, and safe? (Ventral vagal)

This is where polyvagal theory helps us understand why we react the way we do—and how we can shift into regulation.

How Do They Work Together?

The ANS reacts first, and the HPA axis sustains the stress response if your body doesn’t feel safe.

When you're regulated and grounded, your body tells your brain: "We’re okay now."
That simple shift reduces cortisol and helps the HPA axis quiet down.

So, How Do You Heal?

The path to healing chronic stress and overwhelm lies in nervous system regulation—not just “thinking positive.” When we learn how to feel safe, supported, and connected in our body, we rewire the very systems that kept us stuck in survival mode.

Try This:

Start with small, consistent practices: