The Parasympathetic Nervous System: What is it and how do we activate it?

The parasympathetic nervous system, often referred to as the "rest and digest" system, plays a crucial role in maintaining homeostasis in the body. Understanding how to activate this system can have profound effects on our overall health and well-being. But what is the parasympathetic nervous system is the begin with? Why it’s important and how do we support it?

What is the Parasympathetic Nervous System?

The parasympathetic nervous system is one of the two divisions of the autonomic nervous system, which controls involuntary bodily functions such as heart rate, digestion, and respiratory rate. It’s the counterpart to the sympathetic nervous system, which is responsible for the "fight or flight" response. The parasympathetic nervous system promotes relaxation, rest, and recovery, counterbalancing the effects of stress on the body, stimulated by the sympathetic nervous system. So in the absolutely simplest terms possible - parasympathetic is your relaxed self, sympathetic is your stressed out self.

How Does the Parasympathetic Nervous System Regulate Heart Rate & Breathing?

The parasympathetic nervous system regulates heart rate by releasing neurotransmitters such as acetylcholine. Acetylcholine binds to the heart’s pacemaker cells, and helps your body set a slow and steady rhythm. By reducing your heart rate, and the force of your contractions, it helps your body settle into a gentle, relaxed state of being. Similar to the cardiovascular system, with the respiratory system, it’s all about the cadence. The parasympathetic nervous system modulates the activity of respiratory muscles, particularly the diaphragm, leading to slower and deeper breaths.

How Does Parasympathetic Nervous System Relate to the Stress Response?

In times of stress, the sympathetic nervous system becomes activated, leading to physiological changes such as increased heart rate, shallow breathing, and heightened alertness. But we can’t live like that all the time, or our cortisol levels will be through the roof! The parasympathetic nervous system acts as a counterbalance to the stress response, promoting relaxation and restoring the body to a state of equilibrium. By activating the parasympathetic nervous system, we can mitigate the effects of stress on our physical and mental health. However, with the stressors of modern life - think traffic on your daily commute and the constant itch to reach inbox zero - many of us do live in a state of sympathetic nervous system activation. Living in a consistent stress response can lead to a whole host of health implications including digestive problems, cardiovascular diseases, and mental health disorders, so it’s critical to keep this is check [1]. And of course, sauna and cold water therapy are two of our favorite tools that do just that.

How Does Sauna Impact the Parasympathetic Nervous System?

Sauna bathing has significant impacts on the body’s entire autonomic nervous system, but particularly the sympathetic branch. By exposing the body to heat and humidity, saunas induce a relaxation response mediated by the parasympathetic nervous system. This leads to vasodilation, or the widening of blood vessels, which helps increase circulation, and reduce blood pressure and heart rate, leading to a state of deep relaxation and reduced stress. Sauna sessions have been shown to lower levels of stress hormones like cortisol and adrenaline, promoting stress reduction [2]. On the flip side of that, the heat stress experienced in the sauna also triggers the release of endorphins, aka neurotransmitters that promote those happy feelings, so it packs a double punch [3]!

How Does Cold Plunging Impact the Parasympathetic Nervous System?

Cold plunging also has a significant impact on the parasympathetic nervous system, albeit in a much different way than you experience with the sauna. Robert Frost once said, “the only way out is through,” and that’s sort of the case here.

When the body is exposed to cold water, it triggers a physiological response known as the "cold shock response." This response activates the sympathetic nervous system, causing a rapid increase in heart rate and breathing rate, and leading to vasoconstriction, or the narrowing of blood vessels, to conserve heat. At this point, your body’s main objective becomes regulating your core temperature, and the vagus nerve is the big driver here to kick on your parasympathetic response and find a new equilibrium. This shift towards parasympathetic dominance helps restore balance to the autonomic nervous system and contributes to the body's overall relaxation, recovery, and the continual battle against chronic stress.

The human body is amazing. We’re machines with soft tissue and we simply run better when we understand our systems and work to maintain them. By understanding the basics of the autonomic nervous system, you become empowered to make informed decisions in your daily life to support it.

Citing our sources:

1. Fisher JP, Young CN, Fadel PJ. Central sympathetic overactivity: maladies and mechanisms. Auton Neurosci. 2009 Jun 15;148(1-2):5-15. doi: 10.1016/j.autneu.2009.02.003. Epub 2009 Mar 6. PMID: 19268634; PMCID: PMC2679852.
2. Żychowska, Małgorzata, et al. "Effects of sauna bathing on stress-related genes expression in athletes and non-athletes." Annals of Agricultural and Environmental Medicine 24.1 (2017).
3. Laatikainen, T., Salminen, K., Kohvakka, A. et al. Response of plasma endorphins, prolactin and catecholamines in women to intense heat in a sauna. Europ. J. Appl. Physiol. 57, 98–102 (1988). https://doi.org/10.1007/BF00691246