The Brain on Pain: Autonomic Nervous System

As we discussed in the previous blog, Brain on Pain: The Big Picture, pain is vitally important from a survival standpoint.

It protects us from harm to our bodies. When healthy people feel pain, our sensory neurons (that’s the part of our nervous system responsible for giving us the actual feeling of pain) activate our autonomic nervous system, and more specifically our sympathetic nervous system, leading to a “fight or flight” response. In other words, our sympathetic nervous systems prime us for action or an appropriate defense response in the face of danger.

If you’re on a walk and a big dog starts aggressively barking in your direction, most of us feel the instinct to run away. This is the flight response.
Alternatively, you might find yourself driving on the road and suddenly a car swerves into your lane and you brake hard to avoid a crash. This is the fight response.
Our bodies are wired to automatically react to stimuli or events that could potentially hurt us.

Once activated, our sympathetic nervous systems take necessary measures to prepare us: measures like increasing our heart rate so our bodies receive more blood and oxygen, breaking down glucose so we have enough energy to fight or take flight, or slowing down our digestion since it’d be so inconvenient to need to stop for a bathroom break when we need to run away or fight!

While this protective bodily mechanism may have served a very different function to ancestors as they dealt with harsher survival conditions, our bodies still need this mechanism in present-day albeit for different reasons. Tackling a difficult exam, training for a half-marathon, or rushing to make the train during a work commute all require the support of the sympathetic nervous system. 

While our autonomic nervous system, and specifically our sympathetic nervous system, helps us react to pain, it also influences how we feel pain.

Normally, it suppresses the pain experience by blocking pain signals as they are being transmitted—pretty convenient if you’re trying to run from a big dog and take a few stumbles on your escape route. However, in chronic pain states, things look a little different. Research shows that in the face of chronic pain, the sympathetic nervous system may be so worn out that it doesn’t work as well as it is supposed to, leading to blunted response to pain or stressful stimuli and ultimately a stronger pain experience. For example, patients who experience Irritable Bowel Syndrome don’t experience as much variation in their heart rate in response to pain.

Champion Spotlight

There’s probably no better real-life example of an individual who maximized use of their sympathetic nervous system than famed Australian zookeeper and television personality, Steve Irwin.

Steve caught his first venomous snake when he was 6, spent his youth tackling problematic crocodiles for the Queensland government, and the remainder of his life serving an admirable purpose of conserving and expanding wildlife. As he developed his uncanny sixth-sense for wildlife, his refined sympathetic nervous system undoubtedly supported him in his passion, directing him away from danger and giving him the tools to get closer to wild animals than any other human could even venture to try!

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