The ‘fight or flight’ response

  While it is not necessary for the purposes of this book to know the detailed anatomy of the brain, it is useful to know a little bit about the biological and chemical basis of what is known as the ‘fight or flight’ response to stress. Of particular relevance to discussion of the fight or flight response is the autonomic nervous system. This extends from the brain to most of the important organs of the body and consists of two parts, called the sympathetic and parasympathetic nervous systems. Also within the brain is a structure called the hypothalamus, which has two distinct segments that are linked to the autonomic nervous system (see Figure 1.2). One segment is concerned with bodily arousal and is linked to the sympathetic part and the other segment is concerned with the reduction of bodily arousal and is linked to the parasympathetic part of the autonomic nervous system. The hypothalamus thus forms the starting point of the two sections of the autonomic nervous system. The physical consequences of the activation of the two respective parts of the autonomic nervous system on the organs of the body are shown in Figure 1.2.

Figure 1.2 Diagrammatic representation of the structure and function of the autonomic nervous system.

 

  The pituitary gland is a structure linked to the hypothalamus by a small stalk and connected to it by both nerves and blood vessels. It is the ‘master gland’ of the body and produces a number of hormones which control the activity of other glands elsewhere in the body. The most important of these glands in relation to stress are the adrenal glands, which are situated in the kidneys and assist the body to cope with stress by producing hormones. When the brain interprets a situation as being stressful, it triggers the pituitary gland to produce chemical messengers which instruct the kidneys to release stress hormones called epinephrine and norepinephrine into the bloodstream. These stress hormones are pumped around the body and result in the fight–flight response.

Harmful stress

  Under conditions of successful coping, the parasympathetic nervous system is suppressed. However, if the individual is not successful in overcoming the threat and the stress reaction continues without successful resolution for a prolonged period of time, the individual moves into a chronic phase. Examples of such chronic stressors include things like being stuck in a bad marriage, living in noisy or overcrowded conditions, and career or work related problems. In the chronic phase the parasympathetic nervous system becomes overactivated, bodily systems are inhibited and there is decreased physiological arousal, as shown in Figure 1.2. This is achieved through the release by the kidneys of a different stress hormone called cortisol (which is also associated with depression). If the stress continues, the individual eventually becomes physically exhausted and ultimately can become depressed.

The model of stress described here is thus a two stage one characterized by acute and chronic phases. If the individual experiences high levels of stress (acute stress) for a short period of time, it is unlikely to do any lasting harm, but if it continues over a prolonged period of time (chronic stress), it not only has detrimental effects on their performance but also can have harmful longer-term physical and mental consequences. Some of the harmful physical and mental consequences of chronic, long-term, unmitigated stress for both the individual and the organization are reported below.