Autonomic Nervous System: Understanding Sympathetic & Parasympathetic Roles

Nadine Rücker
May 6
3 min read

Updated: Jul 10

Overview

The Autonomic Nervous System (ANS) plays a vital role in keeping your body running smoothly without you even thinking about it. From adjusting your heartbeat to managing digestion, the ANS quietly balances the demands of activity and rest. In this article, we’ll focus on the two key branches of the ANS—Sympathetic and Parasympathetic—and how their opposing actions help your body respond to stress and recover afterward.

The image below shows how the ANS fits into the broader nervous system, highlighting its division from the Central and Peripheral Nervous Systems.

"The Nervous System"
Diagram of the human nervous system divided into Central and Peripheral Nervous Systems. The Central Nervous System (CNS) includes the brain and spinal cord. The Peripheral Nervous System (PNS) is shown branching into the Somatic Nervous System, responsible for voluntary muscle movement, and the Autonomic Nervous System, which controls involuntary actions. The Autonomic Nervous System is further split into the Sympathetic and Parasympathetic branches. — The nervous system is divided into the Central Nervous System (CNS), which includes the brain and spinal cord, and the Peripheral Nervous System (PNS), which connects the CNS to the rest of the body. The PNS is further split into the Somatic Nervous System, which controls voluntary movements, and the Autonomic Nervous System, which regulates involuntary functions. The Autonomic System is divided into the Sympathetic (activates fight-or-flight responses) and Parasympathetic (promotes rest-and-digest activities) branches. Image adapted from https://www.osmosis.org/learn/Parasympathetic_nervous_system.

The Autonomic Nervous System

The ANS regulates your involuntary bodily functions, such as blood pressure, heart rate, breathing, digestion, and more. Imagine your nervous system as a finely tuned balancing act—like a seesaw that constantly shifts between two states: high alert and deep relaxation. At the core of this balance are two critical branches of the autonomic nervous system:

The Sympathetic Nervous System (SNS) – the "Fight or Flight" mode
The Parasympathetic Nervous System (PNS) – the "Rest and Digest" mode

Understanding these two systems is key to optimizing health, managing stress, and improving recovery. Let’s explore how they work and why maintaining their balance is crucial.

The Autonomic Nervous System controls involuntary body functions and is made up of two opposing branches: the Sympathetic Nervous System, which prepares the body for action ("fight or flight"), and the Parasympathetic Nervous System, which promotes relaxation and recovery ("rest and digest"). Their antagonistic effects help maintain balance in the body depending on the situation. Image Source: Adapted from: https://www.standinguptopots.org/ANS101

The Sympathetic Nervous System (SNS): Fight or Flight

The sympathetic nervous system is your body’s built-in survival mechanism. It prepares you for action in response to stress, danger, or even just excitement. When activated, the SNS:

Increases heart rate and blood pressure – pumping more blood to muscles
Dilates pupils – sharpening vision to detect threats
Releases adrenaline and cortisol – boosting energy and alertness
Suppresses digestion and immune function – saving energy for survival
Increases sweating – cooling the body for physical exertion

This system evolved to help us escape predators and react to emergencies. Today, however, modern life overactivates the SNS through constant stress, deadlines, social pressures, and digital overload. Chronic SNS activation can lead to:

Anxiety and burnout
High blood pressure and cardiovascular strain
Weakened immune function
Poor digestion and gut issues

While the SNS is essential for acute stress responses, staying in this high-alert state for too long can be damaging. That’s where the parasympathetic nervous system comes in.

The Parasympathetic Nervous System (PNS): Rest & Digest

The parasympathetic nervous system is the counterbalance to the SNS. It promotes relaxation, recovery, and long-term health. When activated, the PNS:

Slows heart rate and lowers blood pressure – allowing the body to rest
Stimulates digestion – promoting nutrient absorption and gut function
Supports immune function – allowing repair and healing
Enhances sleep quality – reducing stress hormones
Activates deep breathing and relaxation – reducing anxiety

This system is triggered by calm, safety, and restorative activities like deep breathing, meditation, gentle movement, and even social connection. Optimizing PNS activity leads to:

Better recovery from stress and exercise
Improved digestion and gut health
Stronger immunity and reduced inflammation
Enhanced sleep and cognitive function
The See-Saw Effect: Balancing SNS & PNS

The key to a healthy nervous system is not eliminating stress, but managing it effectively. Ideally, we shift between the SNS and PNS as needed —ramping up when necessary and returning to a relaxed state afterward.

How to Shift from "Fight or Flight" to "Rest and Digest"

Deep breathing (4-7-8 method or diaphragmatic breathing)
Mindfulness and meditation
Physical activity (yoga, walking, stretching)
Cold exposure (e.g., cold showers to trigger PNS activation post-exposure)
Spending time in nature
Quality sleep and relaxation rituals

Summary

The sympathetic and parasympathetic nervous systems are like two sides of a seesaw, constantly adjusting to help us survive and thrive. While stress is unavoidable, we have control over how we recover and reset. By actively engaging in relaxation practices and managing daily stress, we can create a resilient nervous system that supports long-term health and well-being.

Which side of the seesaw are you on today?