How Our Body Reacts to Trauma: Part 2

The autonomic nervous system (ANS) plays a critical role in the body’s response to trauma, coordinating involuntary functions to manage acute stress and danger. It consists of two main branches: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS), which have opposing but complementary roles.
 
The sympathetic nervous system (SNS) Response is activated during trauma, initiating the “fight-or-flight” response. This is triggered by signals from the hypothalamus to the adrenal glands, leading to the release of stress hormones such as adrenaline (epinephrine) and cortisol. This results in physiological changes which include increased heart rate and blood pressure to ensure oxygen delivery to muscles and vital organs, increasing rate in breathing and dilation of airways to maximize oxygen intake, heightened alertness as senses like sight and hearing become sharper, and an increase in the release of glucose and fats into the bloodstream for quick energy. If trauma is prolonged or repeated, the SNS can remain overactive, leading to chronic stress, hypervigilance, anxiety, and difficulty sleeping.
 
After the immediate danger passes, the parasympathetic nervous system (PNS) counteracts the SNS by initiating the “rest-and-digest” response. This calms the body and restores homeostasis. Its key functions include slowing the heart rate and reducing the blood pressure, facilitating digestion and energy conservation and promoting relaxation and recovery.
 
Trauma can dysregulate the ANS, causing either hyperactivation (persistent fight-or-flight state) or hypoactivation (freeze or dissociative responses). This is not difficult to imagine like in a battlefield scenario where the soldier is constantly alert for extended days or a person having to face repeatedly being abused without rhyme or reason. This often would result in chronic dysregulation diagnosed as post-traumatic stress disorder (PTSD), where individuals may experience abnormal fluctuations between hyperarousal and emotional numbness. Understanding these responses highlights how trauma impacts both immediate survival mechanisms and long-term physiological health.
 
Additionally, trauma, particularly when experienced during sensitive developmental periods, can lead to long-term changes in brain structure and function. These alterations often affect emotional regulation, memory, decision-making, and stress responses. The major effects may include certain brain regions:

Amygdala:
Function: Processes emotions like fear and anxiety.
Effect of Trauma: Trauma can cause hyperactivation and enlargement of the amygdala, leading to heightened emotional responses and increased sensitivity to stress.

Hippocampus
Function: Plays a key role in memory formation and emotional regulation.
Effect of Trauma: Prolonged stress or trauma can shrink the hippocampus, impairing memory and emotional regulation. This reduction in volume is associated with difficulties recalling positive memories and emotional numbness.

Prefrontal Cortex
Function: Responsible for decision-making, impulse control, and planning.
Effect of Trauma: Trauma can lead to reduced volume or impaired function in the prefrontal cortex, making it harder to regulate emotions and respond flexibly to stressors.
 
Cortical Thickness and Gray Matter Volume
Effect of Trauma: Studies show trauma exposure can result in thinner cortices in regions like the superior frontal gyri and smaller gray matter volumes in areas such as the amygdala and putamen, affecting cognitive functions.
 
Neurochemical Changes
Trauma disrupts neurotransmitter systems (e.g., cortisol,), leading to prolonged stress responses. Elevated cortisol levels can impair neural growth during development and contribute to cell death in critical brain areas.
 
Functional Connectivity
Repeated activation of survival-related brain regions during trauma reduces connections between lower brain areas (responsible for survival) and higher brain areas (responsible for learning, reflection, and planned responses). This impacts emotional regulation, learning ability, and adaptability.
 
Mental Health Implications
Structural changes increase vulnerability to mental health disorders such as depression, anxiety, PTSD, and certain maladaptive coping mechanisms.
 
Reversibility of Effects
Emerging research suggests that some trauma-induced changes may be reversible. Recovery of hippocampal volume has been observed with therapeutic interventions like mindfulness-based practices. Interventions targeting telomere erosion caused by trauma have shown promise in reversing cellular damage. Understanding these long-term effects underscores the importance of early intervention to mitigate trauma’s impact on brain structure and function.
 
The parasympathetic nervous system (PNS) plays a vital role in recovery from trauma by helping the body return to a state of calm and balance after the stress response. Here are ways in which the PNS aids trauma recovery:

1. Restoring Calm and Safety
The PNS counteracts the “fight-or-flight” response triggered by the sympathetic nervous system (SNS) during trauma, promoting relaxation and reducing stress hormones like cortisol and adrenaline. This allows the body to shift from survival mode to a state of rest and recovery.

Activation of the PNS, particularly through the vagus nerve, fosters feelings of safety, connection, and emotional stability, which are essential for healing.
 
2. Supporting Physical Recovery
The PNS facilitates “rest-and-digest” functions, improving digestion, immune response, and cellular regeneration. These processes are often disrupted during trauma but are critical for physical recovery and overall health.
It reduces heart rate and blood pressure, calming physiological hyperarousal caused by trauma.
 
3. Enhancing Emotional Regulation
By calming the nervous system, the PNS helps reduce symptoms of hypervigilance, anxiety, and emotional dysregulation often seen in trauma survivors. This creates space for emotional processing and healing.
 
4. Techniques to Activate the PNS
Several practices can stimulate the parasympathetic response to aid trauma recovery:
Deep Breathing: Slow, controlled breathing activates the vagus nerve, slowing heart rate and promoting relaxation.

Mindfulness and Meditation: These practices help regulate emotions and reduce stress by engaging the PNS.

Physical Activities: Gentle movement that incorporates breathing can enhance PNS activation while improving mood.

​Restorative Practices: Techniques like guided relaxation promote stillness and allow the body to reset its stress response.
Social Connection: Feeling safe in social interactions can activate the “ventral vagal state,” a component of the PNS that supports connection and emotional well-being.
 
By engaging these practices, individuals can leverage their parasympathetic nervous system to facilitate both physical and emotional recovery from trauma.
 
References:
Dumovich, J. & Singh P. (2022, September 19). Physiology, Trauma. NIH National Library of Medicine. https://pubmed.ncbi.nlm.nih.gov/30860713/
 
Muir, W. (2006, December 4). Trauma, Physiology, Pathophysiology, and Clinical Implications. Journal of Veterinary Emergency & Critical Care. Wiley. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1476-4431.2006.00185.x