Thursday, October 12, 2017

Stuff I Learned - ANS

For years, the book The Anatomy of Hatha Yoga sat on my bed stand, and I cannot estimate how many times I read and reread this classic text. In this and other readings, I came to appreciate yoga's influence on the Autonomic Nervous System (ANS), and in particular its potential to shift our response mode from a potentially inappropriate fight/flight/freeze response to a more sustainable rest and digest default status.
The human heart beats at about 100 bpm,
even if disconnected from
neural input.
Among the organs that are influenced by the ANS is the heart and its rate. Heart rate is naturally set to about 100 beats per minute (bpm) by pacemaker cells in the heart. In the absence of ANS input, your heart naturally beats at about 100 bpm. Provided sufficient nutrition, the human heart continues to beat at this steady drum beat even when outside of the body and disconnected from the brain or any other neural input. (please, do not try this at home.)

Your ANS regulates your
heart rate.

While 100 bpm is a pretty functional default heart rate, it's too slow to sufficiently supply blood to your brain and working muscles during exercise, and faster than is necessary to supply your tissues with blood while you're resting. Here's where the brilliance of the body shines forth; your ANS modulates your heart rate to match the needs of your tissues. The rest and digest (parasympathetic) aspect of your ANS acts to lower your heart rate while you're resting. In the adjacent diagram, the shaded portion labelled vagus represents the parasympathetic activation that actively lowers your heart rate while you're resting. The fight/flight/freeze (sympathetic) aspect of your ANS raises your heart rate while you're active or otherwise aroused.

What does this mean for those of us that are living in bodies? Both the sympathetic and parasympathetic aspects of your ANS are essential for optimal health. It can be easy to misinterpret discussions of the ANS and conclude that
  • sympathetic = bad
  • parasympathetic = good
Unfortunately, this simplification is incorrect. What's bad about sympathetic response is not its existence, but the chronicity of its overactivity in our 21st century lives. We need the heart rate to rise when we're active, and it's also vitally important that we have the capacity to relax. Thankfully, regular exercise and contemplative practices like Yoga have the potential to facilitate optimal regulation of the ANS.

In the interest of mental and physical health, are you taking some time each week for physical activity?

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