During a fight or flight response the body automatically prepares itself to fight or flee a threatening situation. The threatening information enters the brain through a sensory portal normally the eyes or ears this triggers the hypothalamus to put the body in a state of high alert.
The hypothalamus is a small part of the brain that instigates changes throughout the body down what is known as the hypothalamic-pituitary-adrenal axis via the blood stream and the nervous system.
Down the sympathetic nervous system stress response route, the hypothalamus releases Corticotropin-releasing hormone (CRH) which is a neurotransmitter that stimulates the release of Adrenocorticotropic hormone (ACTH) from the pituitary gland, an endocrine gland about the size of a pea situated just below the hypothalamus in the brain. ACTH is another hormone that travels in the blood to the adrenal glands which are found on top of each kidney. Once here, the ACTH in the adrenal cortex instigates the release of the stress hormone cortisol.
At the same time, other hypothalamus hormones stimulate the adrenal medulla to release ephinepherine and norephinephrine.
Together cortisol, ephinepherine (adrenalin) and norephinephrine (noradrenalin) spark a number of stress responses throughout the body. The pupils’ dilate to increase the amount of light entering the eye to heighten attention and awareness of the surroundings there is also increased mental activity particularly an enhanced memory. The heart rate is increased and the bronchi are dilated to allow increased flow of oxygen into the lungs. The body will turn glycogen to glucose to raise the blood sugar levels. The body releases energy reserves in muscles to increase strength and energy to either fight or flee.
The rate of blood clotting is increased so if the body was to be physically injured less blood would be lost and pain sensitisation is decreased. In order that the bodies energy be conserved and only be used to aid the survival from a threatening situation, metabolic reactions in the intestines are restricted, tears and digestive secretions are inhibited, regeneration of the immune system is halted, the bladder is relaxed and erection or vaginal lubrication are inhibited. Blood vessels in the skin are constricted and dilated around the organs and muscles that need oxygenating during the fight or flight response.
The fight or flight response aids the rapid preparation of the body to deal with a threat by changing its state into metabolic overdrive; it provides the body with the greatest capacity to survive the sudden danger or threat to life.
However, it is clear to see from an understanding of the stress response that if it is unnecessarily activated or the body does not have a chance to return to a homeostatic state once the danger or threat has been dealt with, the constant metabolic overload can lead to chronic stress.
The majority of people have heard of the fight or flight response but many seem to over look the ‘Freeze Response’ which is equally as important as a means of survival.
The freeze response occurs in nature, often when fighting or fleeing isn’t an option. A mammal will feign death. Animals are hard wired to overlook prey that isn’t moving as a means of self-preservation to avoid disease.
The freeze response is an automatic response to a threat of danger, sometimes it comes after attempting to fight or flee. Other times, it is the instant automatic reaction, instigated by the reptilian brain which is in charge of survival instinct. Durning the freeze response, the control of the neo-cortex which is the area of the brain known to be involved in the processes of logical reasoning is inhibited. Subsequently, the individual losing all power to move or communicate.
As an automatic survival instinct it is almost impossible for humans to ‘override’ it with their intentions.
The freeze response could be highlighted as a fundamental cause of some issues that arise in Post Traumatic Stress Disorder. Often people will experience shame and guilt for not being able to do anything in a critical situation. However, by showing someone that the freeze response is automatic and completely out of the individual’s control, they may be better able to come to terms with the situation.
During a stress response there is the release of neuropeptides, a minute protein the modulates stress by suppressing sleep and increasing alertness and anxiety in order that a person is better able to deal with the threatening stress provoking situation with a strong sense of urgency.
Correspondingly, catecholamins including adrenalin and dopamine restrain the short term memory and focused concentration; additionally it inhibits the frontal brain regions associated with rational thought. The evolutionary role of these changes is that attention and energy reserves are better spent on equipping the body to either fight or flee the threatening situation.
Finally, during a stress response, the hippocampus stores the emotional memory of the stressful event; again this is an evolutionary mechanism that allows the long term memory to store explicit information so that if a person is faced with the same threat the response will occur at an even faster rate.