What Is the Sympathetic Nervous System?

Borderline Personality Disorder Can Inhibit the Sympathetic Nervous System

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The sympathetic nervous system is one of three core parts of the autonomic nervous system. The autonomic nervous system regulations the functions of your organs, such as your heart, stomach and intestines. It also controls muscles in the body; we often do not notice this system at work because it acts reflexively in response to stimulus, such as when your heart starts racing when you are watching a scary movie.


The autonomic nervous system is essential in two ways:

  1. Emergencies: The autonomic nervous system is what stimulates the "fight or flight" reflex when presented with a threat.
  2. Non-emergencies: When no threat is present, it also allows your body to rest, recover and digest nutrients. 

The autonomic nervous system regulates muscles, your eyes, stomach, intestines, bladder and heart.When the sympathetic nervous system is activated, your pupils will become dilated, your heart rate will go up and you will feel primed to run. If you're confronted with danger, such as the sudden appearance of a wild animal when you're out on a run, the sympathetic nervous system controls how you react. If the stress to your body is prolonged, you'll feel a rush of adrenaline released. 

The Sympathetic Nervous System and Borderline Personality Disorder

Borderline personality disorder (BPD) is a common and disruptive mental illness, affecting millions of people within the United States.

Despite its prevalence, little research has been performed to study the neurological or physiological mechanisms behind BPD. Some scientists have suggested that better understanding the mechanics behind BPD, such as issues with the sympathetic nervous system, may lead to the creation of more effective treatment options.

To date, there is no medication approved to treat BPD, unlike other mental disorders.

According to the Diagnostic and Statistical Manual of Mental Illnesses,5th edition, a reference healthcare professionals review when making a diagnosis, those with BPD typically have trouble regulating their emotions. Researchers have hypothesized that this means the sympathetic nervous system in people with BPD may be overly-stimulated, causing intense or irrational reactions. People with BPD tend to display signs of stress longer than others; some studies have found that those with BPD remain in an emotional state 20% longer than other people. 

For people with BPD, the sympathetic nervous system is more easily triggered. Minor situations which wouldn't impact other people can cause an extreme physical response. Stress and anxiety from situations, even if the stress is caused by delusions. For instance, if a person with BPD believes their partner is going to leave her, she may become panicked and distraught, even if her partner has no intention of breaking up with her. Her heart may race, she may cry and she could feel a rush of adrenaline trying to prevent her partner from leaving. 

The cause of this heightened response is unknown.

Some healthcare professionals believe BPD is caused by a mix of biological and environmental factors, including both genetics and how you were brought up. Abuse, trauma and abandonment have all been linked to an increased rate of BPD, but your family's health history also plays an essential role. 


American Psychiatric Association. Diagnostic and Statistical Manual of Mental Illnesses, 5th edition, 2013. 

Austin, M., Riniolo, T., Porges, S. "Borderline Personality Disorder and Emotional Regulation: Insights From the Polyvagal Theory". Brain and Cognition, 2007, 69-76. 

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