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The Autonomic Nervous System
- Liz Lee
- Nov 14
- 4 min read
Updated: 6 hours ago
TLDR:
The autonomic nervous system controls many automatic body functions that keep us alive and healthy. It has two parts: the sympathetic system, which prepares the body for action, and the parasympathetic system, which helps the body relax. The left and right sides of the brain and nervous system have different roles, with the right side linked more to the sympathetic "fight & flight" system and the left side to the parasympathetic "rest & digest" system. Understanding these systems helps explain how our bodies respond to stress, rest, and everyday activities.
By learning about the autonomic nervous system, you can better understand your body’s signals and find ways to support your health and well-being.
The Nervous System in Everyday Life
The human body works like a complex machine, with many systems working together to keep us alive and well. One of the most important systems is the nervous system, which controls everything from breathing, moving your muscles to feeling emotions.
It's pretty complicated, but stay with me!
The nervous system consists of:
Central nervous system (CNS)
Made up of the nerve cells within the brain and spinal cord
Peripheral nervous system (PNS)
Made up of the nerve cells in the nervous system outside (the periphery) of the central channel. These nerve cells connect the organs, sensory systems, muscles with the central nervous system and makes sure the signals from the brain reach all the other parts, and vice versa.
It is also made up of 2 parts
the somatic nervous system - contains the sensory nerves and motor (movement) nerve cells.
The autonomic nervous system - contains the nerves of the body's inner organs that cannot be controlled consciously (involuntary).
Also made up of 2 parts; parasympathetic and sympathetic nervous system.
When it comes to how we react or cope with stress, anxiety and emotional regulation, the important part of the nervous system to understand is the autonomic nervous system. It plays a leading role in managing automatic body functions like heartbeat, digestion, and breathing. This blog will help to explain the autonomic nervous system and how it contributes to our body’s functioning.
What Is the Autonomic Nervous System?
The autonomic nervous system (ANS) is a part of the nervous system that controls involuntary actions. Think auto - for automatic - which means it manages processes that happen without you thinking about them, such as:
Heart rate
Breathing
Digestion
Blood pressure
Body temperature
Elimination (pooping and peeing)
The ANS works quietly in the background to keep your body balanced and ready to respond to changes in the environment. For example, when you exercise, your heart beats faster to supply more oxygen to your muscles. When you rest, your heart slows down to save energy.
The nervous system is divided into two main parts:
Parasympathetic nervous system: Helps your body relax and recover, often called the "rest and digest" system. It slows the heart rate and you have increased blood flow to the stomach to support digestion.
To remember this - this P for Peace
Sympathetic nervous system: Prepares your body for action, often called the "fight or flight" response. It speeds up your heart, opens airways, breathing increases, and releases energy.
To remember this - this S for Stress
Research shows that these two systems work together to keep your body stable, a concept called homeostasis (A term first coined by Walter Cannon in 1932). For example, after a stressful event, the parasympathetic system helps calm your body down.
Did you know: that the nervous system toggles between some level of sympathetic arousal and parasympathetic activation every 90 minutes to 2 hours.
The Nervous System and The Brain
While the autonomic nervous system mainly controls automatic body functions, it also interacts with the brain’s left and right sides. Studies suggest that the right hemisphere plays a bigger role in controlling the sympathetic nervous system, which activates the body during stress (Craig, 2005). The left hemisphere seems more involved in the parasympathetic system, which calms the body.
This means that when you feel anxious or excited, your right brain may be more active, triggering the sympathetic nervous system. When you relax or feel safe, your left brain may help activate the parasympathetic system.
Examples of Autonomic Nervous System in Action
Here are some everyday examples of how the autonomic nervous system works:
During a test: Your heart beats faster, breathing quickens, and your muscles tense up. This is your sympathetic nervous system preparing you to focus and respond by pushing more oxygen to your muscles.
After eating: Your body slows down the heart rate and increases digestion by allowing the muscles in the intestines to contract and move food through, all thanks to the parasympathetic nervous system.
When cold: Blood vessels narrow to keep heat inside your body, controlled by the autonomic nervous system. You may also get goosebumps where the tiny muscles at the base of your hair stand up.
When scared: Pupils dilate to let in more light, helping you see better in danger.
These automatic responses help you survive and adapt without needing to think about every detail.
Why Understanding the Autonomic Nervous System Matters
Knowing how the autonomic nervous system works can help you understand your body better. It is constantly trying to keep you in balance - homeostasis, and allows you to adapt to different environments. For neurodivergent individuals, this knowledge can explain why certain feelings or big reactions happen automatically - out of nowhere. For example, anxiety might trigger a strong sympathetic response, causing a fast heartbeat or sweating. Understanding this can help manage stress through breathing exercises or relaxation techniques that activate the parasympathetic system.
Scientists continue to study the autonomic nervous system to find better ways to treat conditions like anxiety, heart disease, and digestive problems. Research shows that therapies like breathing exercises and mindfulness can improve autonomic balance and overall health (Thayer & Lane, 2000).
References
Thayer, J. F., & Lane, R. D. (2000). A model of neurovisceral integration in emotion regulation and dysregulation. Journal of Affective Disorders, 61(3), 201–216. https://doi.org/10.1016/S0165-0327(00)00338-4
Kreibig, S. D. (2010). Autonomic nervous system activity in emotion: A review. Biological Psychology, 84(3), 394–421. https://doi.org/10.1016/j.biopsycho.2010.03.010
Craig, A. D. (Bud). (2005). Forebrain emotional asymmetry: a neuroanatomical basis? Trends in Cognitive Sciences, 9(12), 566–571. https://doi.org/10.1016/j.tics.2005.10.005
Waxenbaum, J, A. Anatomy, Autonomic Nervous System. [Book]. https://www.ncbi.nlm.nih.gov/books/NBK539845/
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