FIGHT OR FLIGHT

20 Oct

FIGHT OR FLIGHT RESPONSE

The sympathetic nervous system functions like a gas pedal in a car. It triggers the fight-or-flight response, giving the body a burst of energy to respond to perceived dangers. The parasympathetic nervous system acts like a brake. It promotes the "rest and digest" response, which calms the body down after the threat has passed.

These key terms will help you understand the relationship between the brain's emotional and logical centres, the stress response systems (SAM and HPA), and how the body reacts to immediate and prolonged stress.

Critical Terms for Understanding the Stress Response and Brain Functions

Amygdala: A fundamental structure in the limbic system responsible for processing emotions, especially fear and threat detection. It triggers the fight-or-flight response by activating the hypothalamus and plays a critical role in emotional memory.
Corticotropin-releasing hormone (CRH) is a hormone released by the hypothalamus to stimulate the pituitary gland, which releases adrenocorticotropic hormone (ACTH) as part of the HPA axis to manage prolonged stress.
Cortisol: A steroid hormone the adrenal cortex produces in response to ACTH. It helps regulate metabolism, immune responses, and the body's ability to manage long-term stress.
Pituitary Gland: A small gland at the base of the brain that releases several hormones, including ACTH. It is a key component in the HPA axis, regulating stress responses.
Adrenal Cortex: The outer part of the adrenal gland produces cortisol during prolonged stress.
Adrenal Medulla: The inner part of the adrenal gland that releases adrenaline (epinephrine) and noradrenaline (norepinephrine) during the fight-or-flight response, which is triggered by the Sympathetic-Adrenomedullary (SAM) system.
Adrenaline (Epinephrine): A hormone released by the adrenal medulla during the fight-or-flight response. It increases heart rate, blood pressure, and energy levels, preparing the body for rapid action.
Noradrenaline (Norepinephrine): A hormone similar to adrenaline that also contributes to the fight-or-flight response, helping to increase alertness and focus.
Neocortex: The outer part of the brain is responsible for higher cognitive functions such as logic, judgment, and planning. It is divided into lobes and is considered the brain's "strategy centre."
Limbic System: The brain’s emotional centre is located more profoundly in the brain and is more primitive than the neocortex. It includes structures such as the amygdala and hippocampus and is responsible for emotions and memory.
Hypothalamus: A region of the brain located between the thalamus and midbrain. It acts as the control centre for the autonomic nervous system, regulating functions like body temperature, sleep, and appetite. It also plays a crucial role in hormone regulation by producing releasing factors for the pituitary gland.
Hippocampus: A significant component of the limbic system involved in consolidating short-term memories into long-term memory and aiding in spatial navigation. It is located under the neocortex in the medial temporal lobe.
Thalamus: A symmetrical structure within the brain that acts as a relay station between the neocortex and midbrain. It relays sensory and motor signals to the neocortex and regulates consciousness, sleep, and alertness.
Fight-or-Flight Response: The SAM system manages the body's automatic response to perceived danger. This response involves the release of adrenaline and noradrenaline to prepare the body for immediate action.
Sympathetic-Adrenomedullary (SAM) System: The system responsible for the fight-or-flight response. It is triggered by sympathetic nervous system arousal from the hypothalamus and involves the release of stress hormones from the adrenal medulla.
Hypothalamic-Pituitary-Adrenal (HPA) Axis: The system responsible for managing long-term stress by regulating the release of cortisol. It involves the hypothalamus, pituitary gland, and adrenal cortex.

THE AMYGDALAE

The Amygdalae (singular: Amygdala; are two almond-shaped groups of nuclei located deep and within the brain's temporal lobes. The amygdalae are part of the limbic system, a collection of brain structures associated with emotions and instincts. They are essential for processing emotions and triggering survival instincts, such as the fight-or-flight response. The amygdalae are believed to have evolved primarily as part of the brain’s fear response system, a critical function for vertebrates. Without fear, animals and humans would face more significant risks, entering dangerous situations that could lead to injury or death.

The amygdalae are connected to several key brain regions, including the neocortex, hypothalamus, hippocampus, and thalamus. This intricate network is crucial for regulating emotional responses and memory consolidation. The connection between the amygdalae and the hippocampus is vital for learning what to fear, preventing the need to reassess potentially dangerous situations continually. This ability to rapidly assess threats is essential for survival.

Additionally, the amygdalae are closely connected to all of our senses, receiving sensory input from both the external environment and internal organs. This sensory connectivity enables the perception of danger across multiple sensory channels. For example, the amygdalae allow us to visually detect threats, such as predators, or smell danger, such as detecting smoke. The amygdalae also receive input from the neocortex, allowing us to assess new situations or behaviours more efficiently.

When the amygdalae process sensory input associated with danger, they trigger fear or aggression responses, depending on the individual’s perception of their ability to manage the threat. In response, individuals may instinctively engage in fight, flight, freezing, or submission behaviours. However, the extent to which someone relies on these responses is influenced by self-efficacy—their belief in their ability to handle the situation.

The amygdala can override rational brain processing during intense emotional states when a stimulus matches a previously encountered threat or when the threat is unknown. This is called amygdala hijacking, where instinctive reactions occur without cognitive assessment. In such moments, the rational brain—the prefrontal cortex—is temporarily bypassed, causing individuals to act impulsively, often without considering the consequences. This emotional response happens milliseconds before rational brain processing, allowing for swift reactions to perceived threats. During an amygdala hijack, reasoning and logical thinking may be impaired as the emotional brain overrides the rational brain. A flood of hormones is released, causing both physical and emotional alarm, which primes the body for a fight-or-flight response.

When the amygdala detects a dangerous stimulus, it activates the hypothalamic-pituitary-adrenal (HPA) axis, triggering physiological stress responses such as increased heart rate, elevated blood pressure, and heightened arousal—preparing the body for action.

THE SYMPATHETIC-ADRENOMEDULLARY (SAM) SYSTEM: THE FIGHT-OR-FLIGHT RESPONSE

The fight-or-flight response is scientifically known as the Sympathetic-Adrenomedullary (SAM) system. It’s called this because the hypothalamus activates the sympathetic nervous system (SNS), which releases stress hormones from the adrenal medulla. This process prepares the body to react quickly to danger.

THREAT ASSESSMENT: HOW THE AMYGDALA STARTS THE SAM RESPONSE

When you encounter a threat, your brain's amygdala plays a critical role in evaluating the danger. The amygdala, located deep in the temporal lobe, is the brain's centre of emotions and fear. It processes threats across all senses—whether they're something you see, hear, smell, or feel.

Threat Detection by the Amygdala: When the amygdala recognises a danger, like spotting a predator or hearing a loud noise, it quickly assesses the threat.
Amygdala’s Role in Fight, Flight, or Submission: Based on its evaluation, the amygdala triggers different responses: you may feel the urge to fight, flee, or even submit (freeze in place), depending on your assessment of whether you can handle the situation.
Signal to the Hypothalamus: Once the amygdala detects a threat, it immediately sends a signal to the hypothalamus, which acts as the control centre for the stress response.

HOW THE SAM SYSTEM KICKS INTO ACTION

Once the amygdala alerts the hypothalamus, the sympathetic nervous system (SNS) is activated, triggering the fight-or-flight response.

Sympathetic Nervous System Activation: The hypothalamus sends signals to the sympathetic nervous system, which prepares your body for rapid action by increasing alertness and readiness.
Adrenal Medulla Response: The SNS then stimulates the adrenal medulla on top of your kidneys to release stress hormones.
Release of Adrenaline and Noradrenaline: The adrenal medulla releases adrenaline (epinephrine) and noradrenaline (norepinephrine) into your bloodstream, leading to immediate physical changes to help you respond to the threat.

PHYSIOLOGICAL CHANGES DURING SAM RESPONSE

Once adrenaline and noradrenaline flood your system, your body undergoes several rapid changes to prepare for fight or flight:

Heart rate increases: Your heart pumps faster to deliver more blood to your muscles.
Blood pressure rises: Ensuring oxygen and nutrients are quickly transported where needed.
Airways open up: You take in more oxygen, which helps energise your muscles.
Glucose release: Sugar is released from your liver into the bloodstream to boost energy.
Pupils dilate, Allowing you to see more clearly in a stressful situation.

These changes happen within seconds, preparing your body to fight the threat, run away, or sometimes freeze in place.

EXAMPLE: SAM IN ACTION

Imagine a polar bear suddenly confronts you:

Amygdala Alert: Your amygdala immediately recognises the polar bear as a severe threat.
Sympathetic Activation: The amygdala signals the hypothalamus, which activates the sympathetic nervous system.
Adrenal Medulla Response: The SNS triggers the adrenal medulla, which releases adrenaline and noradrenaline into your bloodstream.
Physiological Changes: Your heart rate spikes, blood pressure rises, pupils dilate, and your body is flooded with energy. You are primed for fight/flight or even freezing if the threat feels overwhelming.

In this state, your body is prepared to handle the danger instinctually.

THE HYPOTHALAMIC-PITUITARY-ADRENAL (HPA) AXIS: MANAGING LONG-TERM STRESS

While the SAM system handles immediate threats, the HPA axis manages longer-term stress if the situation continues. This system involves the hypothalamus, pituitary gland, and adrenal glands and helps the body cope with prolonged stress by releasing cortisol.

Hypothalamus: In response to ongoing stress, the hypothalamus releases corticotropin-releasing hormone (CRH).
Pituitary Gland: CRH signals the pituitary gland to release adrenocorticotropic hormone (ACTH).
Adrenal Glands: ACTH stimulates the adrenal glands to release cortisol, which helps your body deal with long-term stress.

Cortisol regulates metabolism and immune response and helps the body sustain energy over extended periods. The HPA axis has a feedback loop that ensures cortisol levels don’t remain elevated once the stressor is gone.

SUMMARY:

The SAM system (Fight-or-Flight) handles immediate threats. The amygdala recognises danger and activates the sympathetic nervous system, releasing adrenaline and noradrenaline, which prepare the body to react instantly.
HPA axis: Manages long-term stress. If the stress persists, the hypothalamus activates the HPA axis, releasing cortisol, which helps the body cope with ongoing challenges.

Both systems protect you from immediate dangers and prolonged stress, ensuring your body can handle different challenges effectively.

Rebecca Sivyer https://sivyerpsychology.co.uk