The influence of stress on pain;
interactions of the mind/body
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The influence of stress on pain;
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| What is stressful? | The physiological response | A mind/body control system |
Stress can be defined as a perceived inability to cope with an unpleasant or painful life situation. The definition is broad as we must include stress due to physical deprivation or abuse and stress arising from within, such as anger, anxiety or grief. Like pain, there is no direct relationship between the stressful situation (tissue damage) and the stress (pain). It is our minds which decide whether a situation is stressful. Air traffic control would be stressful to some. But air traffic controllers are not super cool people, they are trained to deal with air traffic and are confident in their ability to cope with the situations that may arise. Those very people may find public speaking a nightmare.
The brain/mind plays a primary role in identifying a situation as stressful. Memories of past experiences are called up, cultural and social norms apply, and these factors put together a perception of our ability to cope with a situation. A degree of stress which we can cope with may well act as a stimulus to greater achievement. Some people need deadlines in order to be productive. Stress which helps us deal with an emergency is clearly beneficial if it helps us to survive. But repeated stress is distracting at best and at worst progressively destructive. A repeated alarm becomes exhausting even if there is no physical demand being made on the body.
The physiological response to stress is an increase in activity of the sympathetic nervous system and the release of increased levels of epinephrine and nor-epinephrine into the blood stream. These hormones have the same effect as the sympathetic nervous system, that is, vasoconstriction, increased cardiac effort, inhibition of the GIT and other changes such as increased glycolysis in muscles. Two important differences between the nervous and hormonal response to stress are firstly, the effect of the hormones lasts about ten times longer than the sympathetic response as the hormones are removed quite slowly from the blood. Secondly, the hormones reach every cell of the body. In this state of alarm the body is ready for "fight or flight". Either of these activities uses up the glucose made available, and reduces the increased activity of the heart by fatigue and exhaustion. The feelings of fear are replaced probably due to the accumulation of endorphins, by relief and elation
If there is neither opportunity for fight or flight, we may just have to sit still after a frightening episode until the feelings evoked by the stress hormones slowly fade away.
Stress is also accompanied by an increase in the secretions of the adrenal cortex due to raised levels of adreno-cortoci-trophic hormone(ACTH). ACTH is secreted in the anterior part of the pituitary gland under the stimulation of Corticotropin -Releasing hormone (CRH). This hormone is secreted in the hypothalamus in response to stress and conveyed to the anterior pituitary gland through a portal system. The hypothalamus is part of the so called "limbic" system of the brain which was a name used to include the hippocampus, amygdyla, septum and the cingulate gyrus. These areas of the brain all seem related to mood and emotion. Here motivation for behaviour originates in response to emotions such as fear, rage and aggression. When the feelings are resolved there are replaced by relief or satisfaction. Feelings have a biochemical basis. They are partly generated by the levels of endorphins and many other neuropeptides which that make us feel satisfied and content.
There is thus a direct channel of communication between changes in mood and emotion, and the secretions of the pituitary gland and the adrenal cortex. This pathway has been called the hypothalmic-pituitrary-adrenal axis or HPA. The increased levels of cortisol as a result of CRH formation, have a direct negative feedback on CRH secretion and normally this control loop regulates cortisol levels. In the presence of sustained stress the activity of the hypothalamus breaks into this normal regulatory mechanism. The benefit to the body of raised cortisol levels in stress is uncertain. Raised cortisol levels affect mood, behaviour and disrupt memory and reduce serotonin synthesis. Another consequence is depression of the immune system. The HPA system can also raise the level of immune response so it appears to have an important regulatory role. It allows us to understand the direct influence of our emotional state on our susceptibility to some if not all illness. Cells of the immune system carry membrane receptors to many neurotransmitter substances including endorphins. Thus endorphins produced in the hypothalamus influence the activity of both lymphocytes and neurones in the brain stem and spinal cord.
Drugs which act on the mind such as heroine, lithium and Valium attach to specific receptors on cells of the nervous system. These receptors have not evolved in preparation for man made drugs but for the ir endogenous equivalent. Our moods and anxieties are therefore constantly under control of endogenous neuro-peptides. These peptides are to found all over the body, certainly concentrated in some areas such as the limbic system, but not restricted to the brain. They are found on all immune cells and glandular secreting cells, particularly those of the gut. Immune cells also secrete neuro-peptides so the information flow is both ways between the immune system and the brain. This evidence persuades some scientists to view the mind as a flow of information around the entire body, which may be unconscious (Pert 1997). The group of classical neuro-transmitter substances, neuro-peptides, steroid hormones and growth factors which carry this flow have been called information substances.
The information substances operate as a network of influences and information.. The concept of a network implies that any node or point of the network has the ability to change the entire system. There is no heirarchy with gives one system more influence than another. We tend to imagine the brain as the master mind, with "higher" centres like the cortex having control of "lower" centres. This view is supported by the anatomical structure of the brain. Yet there is reason to believe that the structural divisions do not represent clear functional divisions. There is no "pain centre" or "visual centre" or "memory centre" (Greenfield 1997).Connections between regions are more likely to be form a balanced dialogue with each other than converge on an executive centre. Greenfield constructs a new metaphor for the brain as "a bag of hormones with sparks" The ancient eastern view of energy centres also considers that there is a network of energy and information rather than a singly dominant centre. Many alternative healers refer to the bodies innate intelligence.
The focus on the body as a part of the mind can be useful in reducing pain. In a state of meditation practitioners of yogi are able to reduce their respiratory rate and endure pain and cold. Benson (1977) showed that a simple breathing technique, which induced a meditative state of mind actually brought about striking physiological changes such as decreased metabolic rate, lowered blood pressure and lowered respiratory rate. Western scientists refer to breathing techniques as relaxation therapy and find, not surprisingly, but with no attribution to ancient eastern medicine, that it is very effective in reducing pain. Recent evidence adds further understanding of the process. Deep breathing causes a change in the balance of certain peptides, including endorphorphins in the brain stem and in particularly the peri-aquaductal grey area.
Candice Pert (1997) believes that the emotions, and the many peptides that cause these emotions are the conduit between body and mind, going back and forth between the two and influencing both. She writes "At any instant our body is in our mind and our mind is in our body".
Stress is in our body and also in our mind. It makes us feel anxious, short tempered and overwhelmed. The molecules of these emotions lower the pain thresholds set in the peri-aquaductal grey. Pain and suffering add exhaustion, fear and depression. The cycle is a positive feedback. Pain is stressful and stress makes pain worse. If we are to try and reduce one, we will have to reduce both.
Sources and Recommended Reading
Pert C (1997) "Molecules of Emotion- why you feel the way you feel" Simon and Schuster. London.
Benson 1977 in Melzac R and Wall PD "The Challenge of Pain" Penguin 1998.
Shepherd G. "Neuobiology." 3rd edition. Oxford 1994.
Stokes P.E (1995) The potential role of excessive3 cortisl induced by HPA hyperfunction in the pathogeneisi of depression. Eur Neuropsychopharmacol Suppl 77-82.
Greenfield S. (1997) The Human Brain; A Guided Tour" Science Masters Series. Weidenfeld and Nicholson.
This page was prepared by Robin Wilding and last updated on March 25th 2000. Write to RobWilding@eclipse.co.uk with comments or visit Moorland Dentistry