Physiological Responses to Stressful or Traumatic Events: Part I

Part I of this article includes information about how our bodies physiologically respond to a stressful or traumatic event.  These stress reactions are universal and necessary for our survival.  I hope that this information will be useful to you.


Stress as a term by itself is misleading. Instead, there are stressors, stress states, and stress responses.  Stressors are for the most part, subjective.  What is stressful to one person will not necessarily be to another.  Parachuting out of plane for one person is an exciting, uplifting, and in fact calming experience, while to another, causes fear and trepidation; an event to be avoided at all cost.

Stress states can be charted on a continuum, from normal stress to what is known as a dissociative stress state, most often a symptom of post-traumatic stress disorder (PTSD). I am not going to discuss PTSD at this time, rather for now, I want to look at the continuum between normal and chronic stress states.

The stress response, a biological and biochemical process, starts in the brain, spreads to the autonomic nervous system, which in turn causes a hormone release designed to protect and maintain stability in both humans and animals. Survival is the key. Fight, flight, freeze, and appraisal are the mechanisms by which we have survived since the beginning of time.


The brain weighs about three pounds and is composed of mostly water and fat. It is the grand mediator and thus the first system to recognize a stressor.  In fact, it can simulate the stress response for as long as seventy-two hours post incident and also has the dubious ability to arouse the stress response simply by thinking about threat (McEwen & Seeman, 1999, Sapolsky, 1996).

Brain development is use dependent, meaning that stimulation directly affects the growth of neural pathways.  This critical factor in brain development will be discussed at greater length when I introduce the issue of adverse childhood experiences.

The cerebral cortex contains the neocortex, limbic system, and diencephalon, three of the four major sections of the brain, the fourth being the brainstem. It is the largest part of our brain comprising from ten to fourteen billion neurons. If we had the inclination to collect them all in one spot, we’d have a stretch of neurons approximately 2 million miles long (Bruce D. Perry, 2002) (Daniel J. Siegel, 1999).  At the top of the brain, the neocortex, mediates complex “information-processing functions such as perception, thinking, and reasoning” and is the area of the brain which makes us “most uniquely human” (Daniel J. Siegel, 1999).

The limbic system is a tiny, walnut sized system located deep in the center of the brain between the brain stem and the cerebral cortex. Among the divisions making up the limbic system are the orbitofrontal cortex, anterior cingulate, and the amygdala, which all play a central role in coordinating the activity of the higher and lower brain.  The limbic system mediates emotions, motivation, goal directed behavior, including the appraisal of meaning and the processing of social experiences. It is the storage center for emotionally charged memories, controls appetite, sleep cycles, sex drive, and processes the sense of smell (Daniel J. Siegel, 1999; Babette Rothschild, 2000; Joseph LeDoux, 1996; Bruce D. Perry, 2002).

Despite its size, the limbic system is powerful and plays a central role in survival.  Incoming stimuli are first processed, integrated, and given meaning in the limbic system. The orbitofrontal cortex, located behind the eyes is designed to integrate and coordinate cognitive and emotional processes. It helps us to control our impulses and emotional arousal while at the same time reading facial expressions and interpreting interactions with others. Our earliest face to face experiences with caregivers stimulate the neural pathways of the orbitofrontal cortex which, if our caregiver interactions are healthy and functional, will help children to “moderate their frustration, rage, and fear, and to respond flexibly to other people” (Perry, 2002 pg. 5).  The development of these neural pathways plays an important role in a child’s resiliency and in their ability to cope with stressful experiences.

The hippocampus which forms a part of the limbic system is shaped like a seahorse and sits on either side of the brain.  It plays a very important role in learning and memory and is particularly affected by stress.  Studies indicate that chronic traumatic stress can result in an atrophied or smaller hippocampus. This has the consequence of affecting learning in children. Studies are only now uncovering the extent of the damage done to the hippocampus when exposed to chronic stress (Bremner, 2003, Perry, 2003).

The amygdala is a tiny almond shaped structure that is as mighty as it is small. It is important to note that there are more neural pathways connected from the amygdala to the cerebral cortex than from the cortex to the amygdala, which means that it can overpower the cortex (Wylie & Simon, 2002). The amygdala is the storage container for all the frightening experiences one has had through out life.  Most importantly, it NEVER forgets (Joseph LeDoux, 1996).  Interestingly, while the human brain is not fully formed until the early to mid twenties, the amygdala is fully formed at birth. The amygdala is a key player in the stress response and consequently to our survival. Without the amygdala, survival would most certainly be compromised if we were unable to store and recall that fire burns, that certain animals are dangerous, or that precaution is required on the edge of a cliff.


When the amygdala interprets an event to be threatening and scary, it messages the hypothalamus to go into action..  The hypothalamus, located below the thalamus, straddles the diencephalon and the limbic system and is central to the autonomic nervous system (ANS).  Some believe the hypothalamus is a part of the limbic system; however, its importance is in its function and not to what system it is connected. It is, without doubt, an essential player in the stress response and in maintaining homeostasis. This is the central way station for all the automatic functions that go on in the body such as heart rate, blood pressure, goose bumps, and respiration. The thalamus is the relay station for all information except olfactory information coming into the brain.

After the amygdala sends messages to the hypothalamus, it in turn releases the powerful hormone, corticotropin releasing hormone (CRH) to the pituitary glands which induces the pituitary gland to secrete adrenocorticotropin releasing hormone (ACTH).  The ACTH then travels to the adrenal glands which flood the system with adrenal cortisol, setting the fight, flight, freeze, and appraisal system into high gear. The adrenalin keeps us alert and sets the physiological response into action, while cortisol works more slowly and helps the body to replenish its energy supply (McEwen, 1998). The cortisol is designed to contain and to ensure that the system doesn’t run amok.


The ANS is an enormous network of nerves, which branch out from the spinal cord to every organ in the body and is centered in the hypothalamus.  It is responsible for all the automatic functions within our body, which are outside of our control or our awareness.  Dr. Robert Sapolsky in his taped course Biology and Human Behavior: the Neurological Origins of Individuality, comments that the ANS is “an enormously distributed system” that is divided into two different parts (sympathetic and parasympathetic systems) with “very opposing flavors.”

The sympathetic nervous system (SNS) is responsible for releasing adrenalin and is the accelerator responsible for the fight, flight, or freeze response. It is the essential emergency energizer, which profoundly affects the heart.  The hypothalamus starts the whole process going when it sends out “projections” to other parts of the body that there is a threat in the neighborhood. Once the call to arms is sounded, our heart rate and blood pressure increase.  These increases augment the production of glucose and oxygenation to the large muscles for flight readiness. The glucose production is assisted by the shut down of the gastrointestinal tract.  This shut down affects the secretion of saliva, hence dry mouth is typically an early sign that our emergency system has been activated.

The parasympathetic nervous system (PNS) has just the opposite function.  It calms the response by putting on the brakes.  The heart rate slows and our breathing slows and deepens. While the PNS is calming the system, it is also stimulating systems, which shut down during the emergency response such as the gastrointestinal tract so that digestion and elimination can begin anew.  What has contracted in the face of danger can now relax and expand because ostensibly we have let go and acknowledged the end of the threat. Once our threat detection has quieted, the PNS can activate our appraisal system and “safety seeking behaviors” (Macy, R., 2003).   The job of the parasympathetic nervous systems is to restore a sense of wellbeing and harmony to the body.  Understanding how our bodies work and holding the frame that crisis and trauma is in the body can ultimately help to focus our energies so we can hopefully enhance the natural calming effects of the PNS.

The freeze response is as much a part of our survival as the fight or flight response.  Our limbic system assesses the threat and our ability to respond.  If it determines that death is a high probability, our bodies will most likely freeze.  Rothschild (2000) reminds us that the freeze response can actually increase our chances for survival.  Take for example, the possum; their “playing possum” increases the likelihood that their attacker will lose interest with an already “dead” prey.  Humans who enter the freeze state have an altered sense of reality and “time slows down and there is no fear or pain.  In this state, if harm or death does occur, the pain is not felt as intensely,” (Ibid, pg.10).  It is important to be aware, however, that if an individual enters the freeze state routinely, self- esteem can be compromised. Developing mastery and coping strategies are fundamental to self-esteem. (Macy, 2003).


Our children are our most precious investment.  Their needs are of chief importance.  Children who have experienced adverse childhood experiences, which include neglect, physical and sexual abuse, and witness to violence are at risk for multiple emotional, learning, and physical problems. Additionally, even though these children have already been traumatized, they are nevertheless more vulnerable to traumatic reactions following a critical incident.

Drs. Bruce Perry and Vincent Felitti speak passionately about the affects of violence on the growing child’s emotional, intellectual, and  physical life well into adulthood .  The research is compelling and their comments at times heart breaking.

Dr. Perry states that children are not resilient rather they are malleable.  The consequence of malleability is that abused and neglected children are “hammered” into shape and are not able to return to their “original shape” as they would if they were resilient or pliant.  Similarly, they are understandably easily controlled and influenced by their experience.

More insidious is the damage done to the growing and developing brain. Violence and other forms of maltreatment effect learning, impulse control, aggression, the ability to attach or bond to others, self esteem and physical health. The title of one of Dr Vincent Felitti’s (2001) articles on adverse childhood experiences entitled, Reverse Alchemy in Childhood, Turning Gold to Lead, poignantly describes the damage done to an innocent child filled with potential at birth.  Instead that child is born into the vortex of transgenerational abuse (Perry, 1997) where hopefulness and potential are compromised.


Many of my clients in the past have responded to research results about childhood maltreatment by saying, “well I’m screwed!  Why bother?  The answer is you’re only screwed if you think you are!  None of us are responsible for the treatment we received as children.  Children are innocent beings who are dependent upon their caregivers.  Children reasonably expect that the adults in their lives are going to protect them, teach them all the living skills they need to know, and treat them in ways they deserve.  This last phrase is critically important because as any child development professional will tell you, magical thinking is at the center of a child’s developmental process. Magical thinking explains cause and effect for a child despite the fact they most often know the difference between fantasy and reality. That said if a parent is erratic, abusive, and inappropriate with a child, it is most common for children to believe they themselves are responsible for it and deserve the abusive treatment. Perhaps they didn’t make their bed, secretly threw away the peas instead of eating them, or didn’t hide the booze “well enough” from the alcoholic parent. That is often enough evidence to believe they deserved it.   It is far too painful to imagine that a parent or caregiver is at fault…we need our adults to bring safety and security to our lives.  Let’s think for a moment about the innocent, creative five year old experiencing daily or episodic pummeling physically, verbally and emotionally by a parent.  What do you imagine happens to that sweet child?  If that child is going to survive such an environment, he or she has to develop survival skills.  Those survival behaviors can be anything from dissociating, meaning they psychologically disappear from the scene (many survivors of abuse report that they imagine themselves on the ceiling looking down at themselves and their abuser).  Others begin to use substances, that can include food, alcohol, or drugs to self medicate.  Some strike out at others or become the class clown, or isolate, or become caretakers of others.  The list can go on.  What I see as a clinician, far too often, is that my clients carry the belief that they deserve poor treatment within a tired and tattered play script that is glued, with a very strong fixative, to their back pocket.  Their role in the play regardless of the other players is always the same…the behavioral pattern is repeated ad nauseum.

Ok, you say, “I can see it now… I’m Really screwed!”  I’m not writing this information with the intention of leaving you in despair.  Rather I am writing all this to illustrate that a child learns to respond to maltreatment in ways that at the time are adaptive. At the time of the maltreatment, the survival behaviors make sense and are necessary to get through the ongoing ordeal.  BUT learned behavior can be unlearned. Start by celebrating and honoring your survival behaviors…they got you through.  Now however, they are bringing you to therapy, or perhaps to a place of depression or anxiety because they no longer work in the ways they had…that is of course the bad news AND in my book the good news because you are at the now of change.