The Fight or Flight Response

The fight or flight response is an automatic physiological reaction that occurs when the body perceives a threat or danger. It prepares the body to either fight the threat or flee from it. This response evolved to help our ancestors survive physical dangers (e.g. predators) and is controlled by the autonomic nervous system.

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How the Fight or Flight Response Works

When a threat is perceived, the following sequence occurs:

1. Threat Detection

The amygdala (a small structure in the brain involved in processing emotions, especially fear) detects the threat and sends a distress signal to the hypothalamus.

2. Activation of the Sympathetic Nervous System

The hypothalamus activates the sympathetic nervous system (the part of the autonomic nervous system that prepares the body for action). This triggers the adrenal glands to release adrenaline (and noradrenaline) into the bloodstream.

3. Physiological Changes

Adrenaline causes a series of rapid physiological changes:

Change	Purpose
Heart rate increases	Pumps more blood (carrying oxygen and glucose) to muscles
Breathing rate increases	Takes in more oxygen for muscles
Muscles tense	Prepares for physical action (fighting or running)
Pupils dilate	Improves vision and awareness of surroundings
Blood diverted to muscles	Away from non-essential functions (digestion, immune system)
Digestion slows/stops	Energy is redirected to muscles
Sweating increases	Cools the body during exertion
Glucose released into blood	Provides energy for muscles
Pain sensitivity decreases	Allows action despite injury

4. Action

The body is now primed to either:

• Fight — confront and attack the threat
• Flight — escape from the threat as quickly as possible
• Some researchers have added "Freeze" — becoming immobile (like a deer in headlights), which may also be an adaptive response in some situations

5. Recovery

Once the threat has passed, the parasympathetic nervous system (the "rest and digest" system) takes over, returning the body to its normal resting state:

• Heart rate decreases
• Breathing slows
• Muscles relax
• Digestion resumes

Fight-or-flight response flow

flowchart TD
    A[Threat perceived] --> B[Amygdala detects threat]
    B --> C[Hypothalamus signalled]
    C --> D["Sympathetic nervous system<br/>activated"]
    D --> E["Adrenal glands release<br/>adrenaline + noradrenaline"]
    E --> F[Heart rate increases]
    E --> G[Breathing rate increases]
    E --> H["Muscles tense<br/>pupils dilate"]
    E --> I["Digestion suppressed<br/>glucose released"]
    F --> J[Fight, Flight or Freeze]
    G --> J
    H --> J
    I --> J
    J --> K[Threat passes]
    K --> L["Parasympathetic NS<br/>rest and digest"]
    L --> M[Body returns to baseline]

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Evolutionary Basis

The fight or flight response evolved because it helped our ancestors survive physical threats:

• Encountering a predator required either fighting it off or running away
• The physiological changes (increased heart rate, muscle readiness, heightened awareness) gave a survival advantage
• Those who had a strong fight or flight response were more likely to survive and pass on their genes

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The Fight or Flight Response in Modern Life

While the response evolved to deal with physical threats, it is also activated by psychological stressors in modern life:

Modern Stressor	Example
Exams	Anxiety before a test triggers the fight or flight response
Public speaking	Fear of judgement activates the response
Work deadlines	Time pressure causes stress-related activation
Social conflict	Arguments or confrontations trigger the response

The problem is that the fight or flight response is designed for short-term physical threats. When activated by chronic psychological stressors (which cannot be fought or fled from), it can lead to health problems:

• Chronic stress — persistent activation of the stress response
• Anxiety disorders — excessive fight or flight activation
• High blood pressure — due to chronically elevated heart rate
• Digestive problems — due to persistent suppression of digestion
• Weakened immune system — due to chronic diversion of resources away from immune function

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Evaluation

Strengths

• The fight or flight response is well-documented through extensive research
• It has clear evolutionary value — it helped our ancestors survive
• It explains the physical symptoms of anxiety and stress (racing heart, sweating, etc.)
• Understanding the response has practical applications (e.g. treating anxiety, managing stress)

Weaknesses

• The original concept was based primarily on research with male animals — the "fight or flight" may not fully describe female stress responses
• Shelley Taylor (2000) proposed the "tend and befriend" response — suggesting that females may respond to threat by nurturing offspring (tend) and seeking social support (befriend), due to the hormone oxytocin
• The response is less adaptive in modern life — it is triggered by psychological stressors that cannot be physically fought or fled from
• It is an oversimplification — the stress response involves many systems and is more complex than the simple fight-or-flight model suggests

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Key Points

• The fight or flight response prepares the body to deal with threats through physiological changes.
• It is triggered by the amygdala and hypothalamus, which activate the sympathetic nervous system and release adrenaline.
• Key changes: increased heart rate, breathing, muscle tension, pupil dilation, glucose release.
• The parasympathetic nervous system returns the body to rest after the threat passes.
• The response evolved for physical threats but is triggered by modern psychological stressors.
• Chronic activation can lead to health problems including anxiety, high blood pressure, and immune suppression.

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Worked case study: Raine et al. (1997) — abnormal amygdala activity in murderers

While the fight or flight response is best studied through physiological research, a strong case study comes from neuroimaging of individuals with dysregulated threat responses.

Aim: To examine whether murderers who pleaded not guilty by reason of insanity (NGRI) show abnormal activity in brain regions linked to emotion and aggression, including the amygdala — the brain structure that triggers the fight or flight response.