PART 1: Fight or flight response

Our body does not abandon us when facing a life endangering situation. It prepares us to fight with many tools developed during evolution.

The amygdala is an area of the brain that controls our decision making and emotional responses. It´s tasks include fear processing and threat evaluation based on information from the eyes and ears. From what we have learned, a crocodile presents an extremely dangerous threat, and the amygdala instantly sends an emergency signal to hypothalamus. This area of the brain is like a command center that communicates with the rest of the body, and in an alarming situation activates the sympathetic nervous system.

The fight or flight response is activated by the sympathetic nervous system

The sympathetic nervous system triggers the fight or flight response before we knowingly make any decision on how to act. Many things happen very fast. Firstly the hormone epinephrine (also known as adrenaline) and norepinephrine (also called noradrenaline) are released into our system. We notice the effects: rapid pulse and respiration increase oxygen intake for fast action. Blood pressure goes up and extra oxygen is sent to the brain, increasing alertness. Sight, hearing, and other senses become sharper. Blood sugar (glucose) and fats from energy stores are released into bloodstream to give us the extra power we need.

The skin temperature goes up and sweating of palms makes the grip better – should we need to climb to a tree to flee. Digestion is slowed down – all our energy is now needed to stay alive.

All these reactions are caused by very fast chemical processes in our body. Our preparedness for the fight is uncounscious, and we flee away from the crocodile without thinking.

The fight or flight is a term by Walter B. Cannon

The term flight or flight was first named by M.D.  Walter B. Cannon in 1915. He studied in Harvard and continued to teach there at the department of psychology.  Cannon became especially interested in laboratory animals´ physical reactions under pressure.

When he studied the digestion of scared animals, he observed physical changes in the stomach. Cannon was keen to understand in the relation of psychological and physical reactions for stress and continued his studies on animals´ bodily stress responses for twenty years.

Cannon also re-phrased an earlier presented term homeostasis than means internal balance of the body. According to Cannon our body continuously seeks to gain a certain kind of equilibrium. With living beings the organisms are very complex, including the brain and nerves, the heart, lungs, kidneys and more. For their cooperative condition Cannon suggested a term homeostasis. For instance a raise in blood sugar level makes us thirsty and drinking water re-sets the balance.

‘The homeostatic definition of stress: Acondition where expectations, whether genetically programmed, established by prior learning, or deduced from circumstances, do not match the perception of the environment. This discrepancy between what is observed or sensed and what is expected or programmed elicits patterned responses.’

Still in danger

Let´s get back to the threat we were facing. If the crocodile we saw turns out to be  a soft stuffed toy, we take deep breath and laugh out of relief.

If however the threat is real and a fight is unavoidable, the hypothalamic–pituitary gland–adrenal cortex axis (HPA axis or HTPA axis) activates after the first surge of adrenaline subsidises. The HPA axis keeps the sympathetic nervous system up and running as long as needed, until the fight is over.

The adrenal cortex produces hormones that  contribute to release of cortisol. Cortisol is a steroid hormone that has several functions, it for instance controls the blood sugar level during stress reaction. The hormonal effects caused by the adrenal cortex are called indirect stress responses as they work through blood flow.  These effects take place within 20-30 seconds. Immediate stress responses described in the beginning of this article are induced by the sympathetic nervous system and visible in a few seconds.

Recovery of a stress reaction

When the threat has been removed and the brain no longer perceives the environment risky, will the frontal cortex get an ‘alarm cancellation’ message. The sympathetic nervous system reactions dampen and the amygdala makes the parasympathetic nervous system return the body to its normal relaxed state. The fight or flight response is over.

The body needs about 20 minutes to physically recover from an acute stress reaction. An adrenaline surge affects up to an hour. The release of hormones by the adrenal cortex started later and also lasts longer. The cortisol production in the body will seize as well when the danger is gone, and the balance between sympathetic and parasympathetic nervous system is gained.

The stress reaction can be kept on for a very long time. Human are built to face threats and fight for their lives, normally in rapidly escalating situations that are also quickly over. Activation and preparedness to attack are normal reactions, as well as excitement and joy of victory.

Multitasking, taxes, interests, tormenting colleagues, lost phones and broken household appliances – these were non-existent in the early days of the human species. We can not discharge the surge of adrenaline, when our attacker is a phone bill.

The complete set of 5 articles:

  1. Part 1: Fight or flight response
  2. Part 2: Chronic stress – The brain concludes that we are continuously in danger
  3. Part 3: Tools for long term and continuous stress measurement
  4. Part 4: The Moodmetric ring stress measurement and understanding the data
  5. Part 5: The Moodmetric measurement in preventive occupational health 

The picture and information about Walter Cannon