The autonomic nervous system (ANS), which is part of the peripheral nervous system, consists of sensory and motor neurons. These neurons run between the central nervous system and the peripheral organs, such as the heart, lungs, stomach and intestines.   The ANS is largely involuntary and functions below the level of normal conscious awareness.

The two branches of our nervous system

Historically, the ANS has been divided into two branches:  the sympathetic (SNS) and parasympathetic (PNS) nervous systems.

The SNS responds in the face of threat by elevating heart rate and blood pressure. It stimulates the conversion of glycogen to glucose in the liver, dilates the pupils of the eyes and the bronchi. The SNS also shunt blood away from the skin and viscera to the skeletal muscles, brain, and heart, and inhibits peristalsis in the gastrointestinal tract and contraction of the bladder and rectum.

The PNS responds in rest or in the freeze response (see the above discussion of trauma) by slowing down the heart rate, lowering blood pressure, constricting the pupils, increasing blood flow to the skin and viscera, and encouraging peristalsis of the GI tract.

Stress

The diseases of stress are considered as the result of hormonal changes due to activation of the SNS in the face of perceived threat or danger.   When faced with threat or danger, an animal or human must mobilize, activating sources of short-term energy in the form of glucose from muscles and glycogen from the liver.  The arousal response triggers the release of epinephrine in the brain and adrenalin from the adrenal glands.  This stimulates the heart to beat faster and blood vessels to the brain and skeletal muscles to dilate, which constricting the blood vessels to the organs of digestion.

Cortisol

Cortisol is another important hormone released in response to SNS activation.  Its function is to prepare the body to tolerate prolonged states of threat.  Cortisol and related corticosteroids promote the retention of salt, and therefore fluids, which have the long-term effect of raising blood pressure.  Increased cortisol levels can also stimulate brain activity, leading to insomnia and increase serum lipids. This can increase cholesterol, promote storage of calories which can lead to obesity, and promote sustained levels of blood glucose, potentially leading to the development of diabetes.  Prolonged high levels of cortisol can also lead to suppressed immune system function, increasing susceptibility to infection and viruses.

Needless to say, there is a clear link between the levels of chronic stress in our culture and the incidence of heart disease, hypertension, diabetes, and obesity.

There is well-documented scientific research linking childhood trauma and the diseases of stress.  However, the diseases of trauma, such as Fribromyagia, Chronic Fatigue Syndrome, and Irritable Bowel Syndrome, have often been considered psychosomatic.

PTSD

The classic symptoms of trauma and PTSD manifest when the fight or flight response is unsuccessful and we have no choice but to freeze.  If the freeze response is not resolved by a discharge or sequencing in the body, we become susceptible to another range of responses that are not driven by epinephrine, adrenalin and cortisol.  The freeze response is driven by a perceived sense of helplessness. This is associated with PNS activation and abnormally low levels of serum cortisol, and elevation of other neurohormones.  The diseases of trauma lie on a continuum, from those more related to SNS activation (and therefore stress with elevated cortisol) on one end. Others are related to PNS activation (and therefore the freeze response with decreased levels of cortisol) on the other.

Please refer to The Body Bears the Burden:  Trauma, Dissociation and Disease, and The Trauma Spectrum:  Hidden Wounds and Human Resiliency by Dr. Robert Scaer for an excellent, in-depth discussion of trauma and trauma-related diseases.