Essay on the Fight or Flight Response

Published: 2021/11/23
Number of words: 2434


Scholars say that humanity has survived as a species primarily due to their ability to choose between fighting or fleeing when they see a dangerous situation. In essence, this attribute is a physiological reaction that occurs automatically, causing a person to run away from a threat or decide to fight the attacking element. While this concept is identified as a physical confrontational situation, it can also describe any potentially stressful triggers that the mind perceives as threatening. This distinction gives the phenomenon another name: the ‘acute stress response,’ which incorporates the notion of mentally stressful and physical situations.

This essay aims to identify the traits which manifest in human beings as a result of fear. Notably, the fight or flight response is a reaction that happens when the body is exposed to scary or stressful stimuli. Remarkably, these changes are often physiological and psychological as they affect different muscles and mental regions in the body. Essentially, this paper will speak on the additional changes within human beings when one identifies a stressful situation. For example, there are physiological changes such as increased heart rate, more circulation, dilation of pupils, and other actions triggered by the sympathetic systems. The body undergoes a series of changes that make one achieve amazing feats while preparing it for an immediate step towards either a fight or flee response.

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The Changes to The Body

The Brain

The presence of a stressful situation shows the power and potential that the brain has over the body. While some people understand the cerebrum triggers most of the reactions and movements in the body, few know the exact parts of the brain that are responsible for this response. Notably, all activities begin when the eyes perceive the looming danger and transmit the message to the amygdala (Understanding the stress response, 2018). This region is the portion of the brain responsible for analyzing one’s environment and emotionally reacting to the outcomes present. Subsequently, the message of the now confirmed threat is pushed to the hypothalamus, which activates the autonomic nervous system (Understanding the stress response, 2018). Essentially, this structure has two primary components, which are the parasympathetic and sympathetic nervous processes. Therefore, the latter process primarily activates the fight or flight response, which triggers the responses visible to the eye, such as dilated pupils and faster breathing.

The sympathetic system is responsible for the release of catecholamines which guide human beings on how to reach self-preservation. Most of the reactions within the body are stimulated by the release of various hormones and substances making up the catecholamine compounds. For example, the amygdala signals the adrenal gland, which releases epinephrine (Understanding the stress response, 2018). This compound, otherwise known as adrenaline, comes from the adrenal gland medulla and, once in the blood, causes various reactions such as the faster heart rate that most people feel when scared. Moreover, if the threat level increases, the brain releases corticotropin, which triggers adrenocorticotropic hormones into the bloodstream (Understanding the stress response, 2018). Consequently, the cerebrum remains charged and ready for a fight or flight reaction as long as the brain feels the threat is still valid and authentic.

The Heart

An increased heart rate is a common reaction to fear across the board. However, though most people agree with this concept, they are not aware of the changes that causing faster heartbeats. Essentially, the raised heartbeat is meant to circulate more blood to the muscles to make the movements efficient and faster. Scientists studying this singularity tackle it based on two views. One school of thought argues that the increase in heartbeats results from the sympathetic nervous system. In contrast, the other group of scholars concludes that it happens due to a decreased parasympathetic system response.

Wang et al. (2019) describes this issue as an autonomic response triggered by the sympathetic system. Remarkably, these nerves are in place to cause one to seek self-preservation which manifests in either running away or standing to protect oneself from a threat. In essence, the heart experiences an inotropy and chronotropy, resulting in increased output within the cardiac muscles (Wang et al., 2019). Furthermore, this reaction is attributed to the increased stimulation of intracellular transients and cardiac action potentials (Wang et al., 2019). Hence, the study followed the nerve stimulations and the voltage levels using calcium-sensitive dyes, which showed the influence of the sympathetic nervous system on the heart.

On the other hand, Müller et al. (2017) study discusses the faster heartbeats from the point of view of reducing the parasympathetic nerve system (PNS) rather than increasing the sympathetic impulses. In essence, this approach serves as a platform to control the rest phase in human beings. This impulse is crucial in relaxing the body’s muscles and mind in an open or closed setting. Studies on the seabird show that the PNS system is depressed for the reactions witnessed in the body (Müller et al., 2017). Notably, the in-depth study on the bird shows that the autonomic system can be activated by a decrease in PNS activity, making reactions such as increased heart rates emanate from a reduced relaxation impulse. Moreover, the heightened state lasted for two hours, showing the correct rest period one should have to get back to their normal body rhythms (Müller et al., 2017). The argument interprets the variations in heartbeats as a balancing effect where rather than have more sympathetic impulses; it suppresses PNS which automatically leaves the body in a fight or flight situation.


Most people are often oblivious to the change in breathing that occurs when facing a threat till they are out of the dangerous situation. Studies show there are a lot of ventilatory responses to stressors in one’s environment. Nicolò et al. (2017) focused on the aspects of frequency, tidal volume, and other factors that are related to overstimulation of the body from heavy exercise. Notably, most individuals register an increased ventilation rate which emanates from the exposure to stressors such as panic, fear, cold, and pain (Nicolò et al., 2017). For example, when one submerges themselves into some chilling water, an automatic response addresses the cold shock being felt in the body.

Though the reaction typically favors a higher breathing frequency, the tidal volume often remains the same as the one that takes in air rapidly and in a shallow manner. While this reaction is stimulated by the responses in metabolism to the external stimulus, fear often triggers a non-metabolic response in that it is initiated by the brain (Nicolò et al., 2017). Notably, this difference creates a change in frequency and tidal volume as one takes in a much deeper breath when panicking. For instance, some people feel they cannot breathe and hence begin to hyperventilate, while others suffer from hypercapnia where their bloodstream has a build-up of carbon dioxide (Nicolò et al., 2017). Therefore, the autonomic response leads to a rapid increase in breathing balanced by one’s frequency and tidal volume, which is how deep or shallow one breathes.


One is often more potent and capable of incredible feats when they are facing danger. Studies show that an individual’s muscles are engorged with blood as heart rate increases. Notably, these findings are apparent by analyzing superficial veins in the body (Derakhshan et al., 2019). Scientists applied thermal analysis on regions of the head such as the forehead, chin, periorbital area, and cheek to see blood movement in these regions. They discovered that when stressed, the body could send nutrients and oxygen to the muscles, which was detectable through the heat facial cutaneous vasculature changes drawn up in graph form. While this study was purposely intended for detecting deception, its premise applies to autonomic responses that are also defined as stressful mental situations. Hence, the heart and the blood vessels allow for more nutrients and oxygen to reach the muscles in the body, thereby preparing it for a fight or flight decision.


Most people have heard the quote ‘survival for the fittest; however, few understand the role vision plays in this endeavor. When one perceives a threat, the survival instincts in the brain kick in and activate the sympathetic system. Remarkably, this term, also known as the autonomic nervous approach, rapidly changes how organs function. For instance, the eye system experiences a change in its pupils and ciliary muscles. When seeing the danger, the pupils dilate, which directly improves one’s vision.

Additionally, the ciliary muscles in the eye relax, causing one to see much further than you would under normal conditions (Flight & Fight, n.d.). Fong, 2012 studies this phenomenon by showing that the pupil dilates after being triggered by emotional stress, which can happen if one is put in a fight or flight situation (Fong Joss, 2012). Moreover, some individuals also speak to having tunnel vision in a life-threatening situation, especially when choosing the right option among the two available outcomes or as one faces an emergency (Kuhl, 2017). Hence, the body has several reactions to being exposed to threatening situations, which include improved vision causing one to see clearer and further away.

Digestive System

Most people can attest to having a dry mouth when faced with a stressful or threatening situation. Mao et al. (2019) shed light on this through their findings that show it is often triggered by perceived stress resulting from the autonomic system (Mao et al., 2019). In essence, this is a typical reaction if one panics. Studies show that people panic or become anxious when faced with an emergency, triggering the autonomic response, releasing catecholamines, which are neurotransmitter compounds that cause the emission of hormones such as adrenaline into the bloodstream (Derrick et al., 2019). This anxiety causes one to breathe through the mouth, therefore drying it of the saliva normally circulating or triggering gastroesophageal reflux that leads to a dry mouth. Moreover, the nervous system inhibits further gastrointestinal secretion and corresponding movement while also contracting all sphincters (Enteric Nervous System, 2019). This reaction takes blood away from the stomach to fuel the muscles to enable a quick response. Hence, the body is prepared internally for whatever happens when either choosing to run or fight.

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Differences In Gender Regarding Heart Rates

Moreover, further studies show no distinct statistical differences between men and women regarding heart rate fluctuation when it influences the autonomic nervous system. Researchers analyzed the reaction of both male and female participants when faced with postural provocation using cardiac electrophysiology techniques (Hnatkova et al., 2019). Notably, when the postural change occurred, there was a slight difference between men and women, where the females have a heart rate of 5 more beats per minute (Hnatkova et al., 2019). Also, female participants reacted to standing provocation, as illustrated by shifts in the respective sympathovagal modulations. Essentially, the alterations were between sitting, prone, and standing positions. The reactions to stressful situations mimic this study as the scientists sought to discover the psychosocial reactions present in each gender. Consequently, the findings show no marginal or distinguishable statistical difference between men and women when analyzing the psychosocial reactions to autonomic responses.


Generally, everybody has different reactions when faced with a dangerous situation. These problematic instances trigger what is known as a ‘flight or fight response.’ Essentially, this phenomenon is broadly classified to encompass stressors that range from physical confrontations to mental strains in open or closed settings. Though these reactions may vary, they are all governed by the autonomic nervous system, which is influenced by the brain, making it a non-metabolic response. The cerebrum typically relies on two sets of nervous systems to achieve this goal. These are the sympathetic and parasympathetic system. Where the former riles up the body and prepares it for action, the latter relaxes human beings thereby initiating rest and adequate digestion of foods to replenish the lost energy or nutrients. Remarkably, these reactions can manifest in changes in one’s heart rate, breathing, digestion and vision. Most people report hyperventilating more frequently, having a higher heart rate, and some even dry mouths when faced with a stressful situation. Therefore, there should be more awareness and studies targeting this issue as the biological processes can help the body harness all its potential at will rather than only when afraid.


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