It’s easy, as a yoga teacher, to take your students’ behavior personally. The student who skips every chaturanga and spends half the class in child’s pose. The one who takes the most aggressive variation of everything you offer. The one who sobs quietly in pigeon pose for no apparent reason. The one who lies in savasana with their eyes wide open, or quietly rolls up their mat and slips out before it even begins.

We notice these things. And if we’re honest, we sometimes wonder: is it me? Is it them? Are they checked out, resistant, or just not trying?

Here’s a more useful lens: it’s their nervous system.

What you’re witnessing in those moments isn’t effort or attitude or even personality — it’s autonomic state. A nervous system that is highly activated shows up differently on a yoga mat than one that is shut down, and differently again from one that is genuinely at ease. These states aren’t chosen consciously. They’re shaped by what happened that morning, that week, or in some cases, years and decades before your student ever walked through your door.

You may have experienced this in your own practice — arriving wound tight from the day and leaving somehow softer, more focused, more yourself. That shift is real, and it’s physiological. If you want to understand why yoga produces it — and I mean actually understand it, at the level of biology rather than belief — the autonomic nervous system is where you have to begin.

Automatic Doesn’t Mean Untouchable

The word autonomic comes from the same root as autonomous: self-governing. Your autonomic nervous system (ANS) manages heart rate, digestion, pupil dilation, modulates aspects of immune function, glandular secretion, vascular tone, and dozens of other processes that your conscious mind never has to think about. Your heart beats while you sleep. Your stomach churns through lunch while you teach. Your blood vessels constrict when you stand up too fast — and your ANS corrects it before you even notice.

For most of history, this system was considered essentially inaccessible to conscious influence. A background operating system you couldn’t reach from the front end. You were along for the ride.

That assumption has been significantly revised. Researchers have identified specific structures — including a small cluster of neurons in the brainstem called the pre-Bötzinger complex — that help explain why deliberate changes in breathing can influence autonomic state.

It’s one of the more exciting areas of current neuroscience, and we’ll dedicate a full post to it later in this series. For now, it’s enough to know that the old idea of the ANS as completely beyond our influence is no longer the consensus view.

The body, it turns out, has left some doors open.

The Architecture: Brain, Brainstem, and Two Branches

The autonomic nervous system is part of the broader peripheral nervous system — the vast network of nerves that extends from the brain and spinal cord out into every organ, gland, and tissue in the body. But its command center lives primarily in the brainstem and hypothalamus, ancient structures that sit below the cortex (our outermost layer of the brain — the wrinkled surface you picture when you picture a brain) and operate mostly outside conscious awareness.

Think of the brainstem as the building’s utility room: unglamorous, largely invisible, and absolutely critical. It regulates breathing rhythm, cardiovascular function, and basic arousal states. The hypothalamus — a small but powerful region nestled near the base of the brain, just above the brainstem — acts as a master coordinator between the nervous system and the hormonal system. Together, they are constantly receiving information from the body and the environment and making real-time adjustments.

From this central command, two branches extend outward to govern essentially everything:

The sympathetic nervous system and the parasympathetic nervous system.

These two branches reach the same organs — the heart, the lungs, the digestive tract, the blood vessels, the skin — and they generally have opposing effects on them. Where one accelerates, the other decelerates. Where one constricts, the other dilates. You’ve probably heard sympathetic described as “fight or flight” and parasympathetic as “rest and digest,” and while those shorthand labels are useful starting points, they’re incomplete in ways that matter for yoga teachers. Each branch is nuanced, layered, and physiologically rich — rich enough that we’ll give each one its own dedicated post in this series.

They Never Fully Turn Off

Here’s where a lot of wellness education goes sideways: the sympathetic and parasympathetic branches are not a light switch. They are not on or off. They are not enemies.

At every moment of your life, both branches of the autonomic nervous system are active simultaneously. What changes is the ratio — which branch is more dominant, and by how much. Even in deep, restorative sleep, your sympathetic nervous system maintains a baseline of tone. Even in an acute stress response — a fight-or-flight moment — your parasympathetic system doesn’t go completely silent.

In fact, the nervous system can produce responses beyond fighting or fleeing. Sometimes the body becomes still and immobilized — a state often described as freeze — while in other situations a vasovagal response can lead to lightheadedness or even fainting. These responses reflect shifting patterns of sympathetic and parasympathetic activity, and they are a reminder that the nervous system’s responses to threat are more varied and complex than the “fight or flight” shorthand suggests.

For a long time, physiologists described the ANS as pursuing homeostasis — the idea that the body maintains fixed, stable set points and that health means returning to them after any disruption. Blood pressure at X, temperature at Y, cortisol at Z. Deviate, correct, return. It’s a tidy model, and it’s not entirely wrong — but it’s incomplete.

The more accurate picture is allostasis: the body achieves stability not by returning to fixed points, but by continuously adjusting those set points based on what life is currently asking of it. It’s predictive and adaptive rather than reactive and rigid. And it involves real trade-offs, because resources are finite. When the ANS floods the muscles with blood during a stress response, it pulls from digestion. When it sustains elevated cortisol to manage ongoing demands, it borrows from immune function, sleep quality, and reproductive health. The body is always robbing Peter to pay Paul.

When life allows for recovery — when the borrowing gets repaid — the system remains resilient. But when the demands are chronic and the debts accumulate unpaid, the physiological cost of that sustained adaptation adds up. Researchers call this allostatic load, and it’s one of the central mechanisms behind the persistent nervous system patterns we’ll be returning to throughout this series.

That capacity for flexible, fluid movement between states — mobilizing and then returning to baseline, activating and then genuinely settling — is increasingly understood to be one of the central markers of physiological health. The goal isn’t calm. The goal is flexibility.

Why This Matters in a Yoga Room

Your students walk into class already in some autonomic state. It was shaped before they arrived — by their commute, their sleep, their last conversation, and patterns that may go back years or decades. They don’t check that state at the door.

Your class is an environment. The way you sequence, pace, cue, and — for those trained to offer it — touch, either works with the nervous system or against it. A student who arrives in a low-activation state — already sluggish, flat, or shut down — may struggle to meet the demands of a fast, intense flow, skipping every chaturanga and retreating to child’s pose not because they’re lazy or unwilling, but because their nervous system is operating in a low-activation state that makes mobilization harder. Conversely, a student who arrives in high-activation — wired, anxious, or still running on adrenaline from the day — may find it genuinely impossible to settle into a slow yin class, fidgeting through every long hold and lying in savasana with their eyes open and their mind reeling.

Neither student is doing yoga wrong. Their nervous systems are doing exactly what nervous systems do.

You don’t need a neuroscience degree to teach yoga well. But understanding the basic framework of the ANS — what it is, what it governs, how its two branches function in dynamic balance — gives you a lens that makes your existing intuitions more precise.

This series is about building that lens, one layer at a time. In the posts ahead, we’ll go deep into the sympathetic branch, the parasympathetic branch, and the emerging science around how bottom-up practices — movement, breath, touch, sound — can influence this system in ways we’re only beginning to measure and understand.

The nervous system is not background noise in your classroom. It’s the whole conversation.

This episode is essentially the science behind why RBM exists. Chapter 1 of Hands-On Yoga Assists — The Science of Safe Touch — picks up exactly where we left off today. [Start with the book.]

The Autonomic Nervous System: Your Invisible…