When we hear fight-flight response, what does this actually mean, neuroscienctifically?

The sympathetic response in the nervous system, referred to as fight-flight, is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to our survival. It is activated through neuroception, meaning threats are detected by our nerves and neurosignals are transmitted to the amygdala in the brain, after which our innate defence mechanisms come online in the autonomic nervous system . This stress response is primarily mediated by (an on/off method) the secretion of these glucocorticoids through the hypothalamic-pituitary-adrenocortical (HPA) axis, as well as triggering the sympathetic-adrenomedullary axis (SAM) to release catecholamines through adrenergic neurotransmission. This all then circulates through the bloodstream and the brain.

When the brain recognises something as dangerous or life threatening, it signals the activation of the sympathetic nervous system. First the hypothalamus releases corticotropin-releasing hormone (CRH), which signals the pituitary gland to release adrenocorticotropic hormone (ACTH), which in turn travels to the adrenal glands and is given the signal to secrete and release cortisone and cortisol – our ‘stress hormones’. These hormones are synthesised and derived from our cholesterol. They are secreted by the middle region of the adrenal cortex.

Catecholamines are biochemicals made by the nerve cells and are used to send the signals to other cells. They include dopamine (for alertness), adrenaline (increases heart rate and metabolism) and noradrenaline (constricts blood vessels, causing increased blood pressure). Noradrenaline is the main neurotransmitter of the sympathetic nerves in the cardiovascular system, while adrenaline is the main hormone secreted by the adrenal medulla. These are released into the blood stress in response to physical or emotions stress. They help transmit nerve impulses in the brain, increase glucose and fatty acid release for energy, dilating bronchioles (decreasing resistance in the respiratory airway and increasing airflow to the lungs), and dilate the pupils. They include dopamine, adrenaline, noradrenaline.

Both catecholamines and glucocorticoids have a huge role in controlling and regulating our ion transport and glucose metabolism during periods of stress. They control metabolism in our muscles, fat, liver and bone. (Cortisol influences the metabolism of fats, proteins to maintain blood glucose within a narrow optimal range and keep it there even under stressful conditions). They affect our vascular tone, influence our immune response and metabolic function, sleep cycles, HRV, mood, memory processing, thoughts, behaviours, energy levels, cravings (high levels of corticoids running in the blood stream causes hypermetabolism, resulting in cravings for sugar, caffeine, greasy, processed foods, all which keep the internal system upregulated).

These biochemicals accommodate us in a time of perceived danger. They offer us the mobilised and upregulated energy which is needed to fuel the fight-flight response in our nervous system and move our bodies into fast action: upping the heart rate and our breathing, increased salvation, rushing blood and oxygen away from the digestive system and sexual space and directed to our vital organs (such as the heart and lungs) as well as to the Deep Front Line region (ie muscles we rely on to act under stress such as the back muscles and quads). In the brain, adrenaline pushes the amygdala further into activation (the gland that is our smoke detector in the brain) while cortisol reduces the activity of the hippocampus (our learning and memory centre).

A whole host of physiological bio chain reactions and byproducts occur when you are in a stressed state. This all happens outside of our conscious awareness and control, with the ultimate goal of the nervous system being, “I need to keep you safe”. Its intention is complete preservation of self.