BIOLOGICAL ASPECTS OF STRESS.

To be able to understand what stress does to the human body, we have to take a closer look at how the body works, in particular the nervous system.

The nervous system can be divided in two different parts: the somatic nerve system which ensures that external stimuli are processed. This section includes the senses and can control muscles to respond to external stimulants. The other part of the nervous system is the autonomic system. This works, like its name implies, independently. This part controls the interior of the body, such as the digestive system, breathing, glands and heartbeat.

This autonomic part can be divided into two parts as well; we can separate a parasympathetic and a sympathetic part. The parasympathetic part tries to bring the body to a state of calm, in order to save energy and to work on rehabilitation and construction. The sympathetic part is the part that is activated by stress: the body is in a state of readiness. This situation requires energy.

This means that activity from the sympathetic nervous system leads to a state of the body that is not rest or aimed at saving energy. All energy and blood goes to the skeletal muscles, because of the fight-or-flight reaction: you are ready to run away. There is hardly any energy or blood for the digestive system.

Two major stress hormones are adrenalin (epinephrine) and noradrenalin (norepinephrine). These hormones are made in the adrenal glands and they affect the sympathetic nervous system; they accelerate the heart rate, increase respiration and ensure that energy is released. They make that the body gets to an increased state of alertness, and so begins the first phase of the general adaptation syndrome.