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  • Alainnah Knight

How The Autonomic Nervous System (ANS) Is Impacted By Trauma

Trauma can have lasting effects on the autonomic nervous system (ANS), which plays an important role in regulating involuntary bodily functions. The ANS consists of two branches: the sympathetic nervous system (SNS), often associated with the fight-or-flight response, and the parasympathetic nervous system (PNS), responsible for the rest-and-digest response.

Trauma, especially complex and prolonged trauma, can result in an overactive sympathetic nervous system (SNS), leaving individuals in a chronic state of heightened alertness and anxiety. At the same time, the parasympathetic nervous system (PNS), responsible for relaxation and recovery, can be impaired, making it challenging for individuals to feel calm. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, reduced heart rate variability (HRV), sensitization to threat cues, neurobiological changes in the brain, long-term health consequences, and difficulties in emotional regulation are just a few of the multifaceted impacts of trauma on the ANS. Recognizing these complexities is crucial for implementing trauma-informed care that addresses both the psychological and physiological aspects of trauma, supporting a holistic approach to the recovery of trauma. Let's dive into a few ways trauma impacts the ANS.

An anatomical model that has half a face and is showing the skull on the other side alongside the organs within the body.

Trauma's Impact On The Autonomic Nervous System (ANS)

Heightened Sympathetic Activation

Trauma can lead to chronic activation of the sympathetic nervous system. This heightened state of arousal is often called the "flight-or-flight" state. In this state, we will often feel on edge, tense, unable to relax or sit still, or have racing thoughts even when nothing threatening is happening. In the long-term, this can look like being a workaholic, a people pleaser, constantly second-guessing, having digestive issues, and problems sleeping at night.

Impaired Paraympathetic Regulation

When we have lived in a chronic state of parasympethetic nervous system activation, our sympathetic nervous system, which is responsible for the "rest-and-digest" state, can become impaired. We may not be able to regulate emotions, can become triggered easily, or not ever have experienced feeling "calm." This is caused by living in a constant state of hyperarousal.

Dysregulation of The Hypothalamic-Pituitary-Adrenal (HPA) Axis

The hypothalamic-pituitary-adrenal (HPA) axis is a key componenet for our stress response systems. This system releases adrenal hormones, such as cortisol, which activates the sympathetic nervous system pathways. Cortisol is a hormone that is produced in order to help us regulate stress. When the system that is responsible for helping regulate and produce this hormone is dysregulated, we begin to neurally and hormonally react to stress in different ways. This can result in being easily triggered, not being able to handle stress effectively, or being depressed.

Sensitivity To Threat Cues

Having experienced a trauma can increase sensitivity to any cues associated with the threat or danger. Triggers can include smells, textures, time of day or year, places, memories, and so much more. Sometimes we may not even know that we are being triggered on a conscious level, but our bodies have been reminded of a time that they were threatened or in danger and responding as if you are in that experience again. This heightened sensitivity can lead to exaggerated sympathetic activation in response to perceived threats, even when they are not objectively present.

Impact on Emotional Regulation

The ANS is closely tied to emotional regulation, which helps us stay in our window of tolerance. When we have experienced trauma, it can become difficult to regulate our emotions even after just something "minor" has happened. This can lead to intense emotional responses, being in prolonged states of hyperarousal, and feeling tired or drained.


Understanding the impact of trauma on the autonomic nervous system (ANS) is such an important step in a journey of healing from trauma. Trauma-focused therapies, mindfulness practices, and interventions that address the physiological effects of trauma can play a beautiful role in supporting you in this journey.


Center for Substance Abuse Treatment (US). Trauma-Informed Care in Behavioral Health Services. Rockville (MD): Substance Abuse and Mental Health Services Administration (US); 2014. (Treatment Improvement Protocol (TIP) Series, No. 57.) Chapter 3, Understanding the Impact of Trauma. A

Kuhlman, K. R., Vargas, I., Geiss, E. G., & Lopez-Duran, N. L. (2015). Age of Trauma Onset and HPA Axis Dysregulation Among Trauma-Exposed Youth. Journal of traumatic stress, 28(6), 572–579.

Murphy, F., Nasa, A., Cullinane, D., Raajakesary, K., Gazzaz, A., Sooknarine, V., Haines, M., Roman, E., Kelly, L., O'Neill, A., Cannon, M., & Roddy, D. W. (2022). Childhood Trauma, the HPA Axis and Psychiatric Illnesses: A Targeted Literature Synthesis. Frontiers in psychiatry, 13, 748372.

Sherin, J. E., & Nemeroff, C. B. (2011). Post-traumatic stress disorder: the neurobiological impact of psychological trauma. Dialogues in clinical neuroscience, 13(3), 263–278.

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