The Sympathetic Nervous System and How the Body Processes Pain

The nervous system of the human body controls and maintains functions of the body.  The somatic nervous system is responsible for voluntary actions, such as walking or eating.  The autonomic nervous system is responsible for involuntary actions, such as digestion, heart rate and sweating.  The autonomic nervous system is further divided into the sympathetic and parasympathetic nervous systems.  Their functions are often simplified into the “fight or flight” system (sympathetic) or the “rest and digest” system (parasympathetic). 

The sympathetic nervous system is activated when we are confronted with a situation that is frightening or exciting or that we believe  will be frightening or exciting.  It then reacts to the stimulus by preparing the body to react to danger – increasing heart rate, blood pressure, sweating, and dilating pupils.  It also shuts down activities in the gastrointestinal system and reproductive system to preserve resources for countering immediate threats.

What does this have to do with pain?

Among the things that the sympathetic nervous system can do is decide which stimuli from pain receptors are allowed to reach the brain and consciousness.  When you have an acute (sudden-onset) injury, you may actually not feel pain, as the sympathetic nervous system sends signals to the tissues to reduce the transmission of pain signals to the brain.  When you are recovering from tissue damage, pain signals may be amplified to prevent you from re-injuring the tissue.

Pain and tissue damage do not necessarily go hand-in-hand.  Neuroscience research has demonstrated that tissue damage does not always result in pain.  Similarly, pain can exist without any evidence of tissue damage. When pain becomes chronic (long-lasting), it may result from long-term activation of the Sympathetic Nervous System.  Called “central sensitization,” a person’s nervous system may be hypersensitive to stimuli. This can be accompanied by changes in both the signal reaching the brain and the parts of the brain itself that sense and react to pain.  

Studies on stress and pain have found that people who are under chronic stress often present with physical symptoms such as pain in the neck and low back.  This is generally believed to be the result of excessive stress on the sympathetic nervous system, which can cause increased adrenaline to be released into the body, as well as activating the endocrine functions that release cortisol into the body.  The excess adrenaline results in the fight or flight response and associated anger and anxiety. The excess cortisol results in emotions of defeat and despair. People under chronic stress may vacillate between anger and despair.

These same mood alterations are often seen in people with chronic pain.  In addition, long-lasting chronic pain and stress is associated with other conditions such as insulin resistance, cardiovascular disease, anxiety, and cognitive issues.  Stress has also been indicated as a factor in chronic inflammation.

So what can be done?

If you have pain without a definitive cause “in the tissues,” what can you do?  The first step recommended is to become educated on the nature of pain. Your pain is an output of the brain that results from input from the brain and the sensory nerves that lead to a perception of threat.  It may not be a reflection of actual damage to the tissues.  

The second step is to take actions that can reduce chronic stress and alter the perception that is being output from the brain.  Stress management techniques recommended for people with chronic pain include:

  • Cognitive behavioural stress management
  • Relaxation, cognitive restructuring and coping skills training
  • Exercise
  • Yoga
  • Meditation

Studies of yoga and mindfulness techniques such as meditation have shown that these techniques have been successful in reducing people’s sensitivity to pain stimuli.  In addition, regular practitioners of mind-body practices have changes in their brain structures opposite of those who have chronic pain.

Can Massage Therapy Help?

Studies on the physiological effects of massage therapy have demonstrated that a single massage session can result in lowered heart rate, lowered blood pressure, and lower levels of substances associated with the stress response.  Although massage alone may not result in long-term stress reduction, it can be a tool used along with exercise and other stress-reduction techniques to aid in management of chronic pain symptoms.


References

Pongratz and Straub:  The Sympathetic Nervous Response in Inflammation.  Arthritis Research & Therapy 2014 16:504

Bushnell, Case, Ceko, Cotton, Gracely, Low, Pitcher and Villemure:  Effect of Environment on the Long-Term Consequences of Chronic Pain.  Author manuscript available in PMC 1 April 2016.  Published in its final form Pain 2015 April 156(0 1):S42-S49

Gifford and Thacker.  A clinical overview of the autonomic nervous system, the supply to the gut and mind-body pathways. Topical Issues in Pain 3.  Sympathetic Nervous System and Pain. Pain Management. Clinical effectiveness  L. S. Gifford (Ed). Falmouth, CNS Press: 21-52. 2002

Malfliet, Leysen, Pas, Kuppens, Nijs, Van Wilgen, Huysmans, Goudman, and Ickmans: Modern Pain Neuroscience in Clinical Practice:  Applied to Post-Cancer, Paediatric and Sports-Related Pain.  Brazilian Journal of Physical Therapy.  2017; 21(4):225-232.

Moraska, Pollini, Boulanger, Brooks and Teitlebaum:  Physiological Adjustments to Stress Measures Following Massage Therapy: A Review of the Literature eCAM 2010; 7(4):409-418.

Crawford, Boyd, Paat, Price, Xenakis, Yang, Zhang and the Evidence for Massage Therapy Working Group: The Impact of Massage Therapy on Function in Pain Populations—A Systematic Review and Meta-Analysis of Randomized Controlled Trials: Part I, Patients Experiencing Pain in the General Population.  Pain Medicine 2016; 17:1353-1373