Fight-or-flight response: what Cannon described and what happens in the body

The fight-or-flight response is the fast reaction of the sympathetic nervous system to a threat that the brain sees as danger. The adrenal medulla releases adrenaline and noradrenaline within seconds, and a slower hormonal chain then holds the arousal with cortisol. Freeze, fawn and tend-and-befriend are later additions, not part of the first description.

Most short guides miss three points that matter for exams and for real life:

• The fast surge and the slow backup use different glands, different hormones and different time scales.
• The calming branch does not trigger the response. It stops the response.
• Walter Cannon did not describe freeze or fawn. Those terms came decades later from other researchers and clinicians.

What the fight-or-flight response is

The fight-or-flight response is a set of rapid body changes that prepare an animal to confront a threat or to escape from it. The trigger can be physical danger, such as a car that moves toward you, or a perceived threat, such as an exam that starts in five minutes. The brain treats both as danger when it sees harm.

Walter Bradford Cannon first described the pattern in the early 1900s and coined the phrase. Britannica notes that he first set out its functions then. In 1914 he published the emergency function of the adrenal medulla in pain and the major emotions (Cannon, 1914). In his 1915 book he called the pattern the necessities of fighting or flight (Cannon, 1915, p. 211, via Wikipedia).

Cannon studied cats and dogs that faced fear or rage. He found the same pattern each time: a racing heart, a halt in digestion, sugar moved into the blood, and blood sent to the muscles. Simply Psychology summarises these animal studies. The response is general. The body uses it for many threats, not one fixed reflex.

The two pathways in one table

One surge starts the response, and one chain holds it. Mix-ups come from treating them as one event.

The table follows the SAM and HPA distinction that Simply Psychology sets out with its pathway steps. Exams often test the middle rows. If the question names seconds, adrenaline or the medulla, the answer is SAM. If it names minutes, cortisol or CRH and ACTH, the answer is HPA.

Threat detection starts before conscious thought. The amygdala flags danger and alerts the hypothalamus. Harvard Health describes this alarm step. The hypothalamus then drives the sympathetic branch, which fires directly onto organs and prompts the adrenal medulla.

What happens in the body

Adrenaline brings rapid changes. The heart beats faster and pushes blood to muscles, heart and other vital organs. Pulse and blood pressure rise. Breathing grows rapid. Small airways open wide and take in more oxygen with each breath. Extra oxygen reaches the brain, and alertness rises. Sight, hearing and other senses sharpen. Adrenaline also frees glucose and fats into blood and gives muscles fuel. Harvard Health lists these changes in order.

The list follows Harvard Health and Britannica on tachycardia, perspiration, tremor and glucose from glycogenolysis. The wiring is fast. The amygdala and hypothalamus start the cascade before visual centers finish their work. That is why a person can jump from a car before thought forms.

When the surge fades, the HPA chain can hold arousal. The hypothalamus releases CRH, the pituitary releases ACTH, and the adrenal cortex releases cortisol. Cortisol keeps blood sugar high and holds back digestion and immune work so energy stays free. Harvard Health describes this second stage. When the threat passes, cortisol falls and the calming branch damps the response.

The body often needs 20 to 30 minutes to return to baseline and calm down. Cleveland Clinic gives this time range. The exact time differs by person and by trigger.

Sympathetic vs parasympathetic

The autonomic nervous system has two branches with opposite jobs. The sympathetic branch acts as a gas pedal. It triggers the surge and gives energy to respond. The parasympathetic branch acts as a brake. It promotes rest and digest and calms the body after danger passes. Harvard Health uses this pedal and brake image.

Use this test for any example. If the change adds energy for action, it is sympathetic. If the change restores digestion, slows the heart and returns baseline, it is parasympathetic. The calming branch uses acetylcholine and works in large part through the vagus nerve. It does not start fight-or-flight. Exams test this reversal often.

Where freeze, fawn and fright fit

Cannon described fight or flight. Later writers added more responses for cases where fight or escape fail or do not fit.

Freeze means the body holds still and stays alert. Muscle tone stays high while movement stops. In humans the state is often brief, lasts seconds, and pairs high arousal with a slower heart rate from vagal braking. Freezing is best read as flight-or-fight put on hold, not as calm. Kozlowska and colleagues set out this cascade model.

Faint, flop and fright name deeper shutdown states. They involve limp muscles, a strong vagal surge, a drop in blood pressure and sometimes loss of consciousness. They occur as last-resort responses to inescapable threat. Wikipedia cites Bracha's 2004 spectrum of freeze, flight, fight, fright and faint. These terms do not come from Cannon.

Fawn means appeasement of a threat through pleasing, compliance or submission. The psychotherapist Pete Walker named it in 2013 from work with complex trauma. It is the least studied of the four and rests on clinical work rather than lab research. Simply Psychology notes this source and limit. Treat fawn as a clinical description, not as an established lab finding.

A common error is to call the whole set Cannon's model. A precise answer names Cannon for fight-or-flight and names the later source for each addition.

Tend-and-befriend: a different proposal

In 2000 Shelley Taylor and colleagues proposed tend-and-befriend as another response to stress. Under threat, people may protect young, care for others and seek social contact and support networks. They linked the pattern to oxytocin and argued that fight-or-flight fits less well for a person who cares for dependent young. They also noted that early stress research used male participants in large part, which may have hidden this pattern. Simply Psychology summarises the proposal and its hormone link.

Tend-and-befriend is a proposal, not a replacement. Teach it as an alternative that fits some cases, above all care of young and social support. Do not present oxytocin as a proven trigger in the same sense as adrenaline in SAM.

What it is not

Rest-and-digest is the recovery, not the surge. It names parasympathetic work after danger: slower heart, renewed digestion, return to baseline. If a question asks what calms the body, the answer is parasympathetic rest-and-digest, not another surge.

A panic attack is a false alarm, not proof of danger. The body fires the same arousal without a real threat, then reads its own pounding heart as more danger. In PTSD the threat system grows sensitive, and harmless reminders can retrigger full arousal with hypervigilance and startle. These outcomes show a system built for acute threat, not for constant psychological load.

Burnout is not the same as the acute response. Burnout is an occupational phenomenon from chronic workplace stress, not a medical diagnosis. Our article on burnout is an occupational phenomenon, not a medical diagnosis sets out what ICD-11 covers. Link the two with care: repeated surges can harm health, but burnout has its own definition and context.

Repeated activation carries cost. Research links chronic stress to high blood pressure, artery deposits and brain changes tied to anxiety, depression and addiction. Early work also links it to weight gain through appetite and through lost sleep and exercise. Harvard Health hedges these links as research suggests, with obesity links as more preliminary. State them with the same hedge.

If stress harms daily life, relationships or work, or brings panic, dread or numbness that lasts, talk to a healthcare provider. Cleveland Clinic advises professional help at that point. Therapy, medication and stress-management methods can help regain balance. This article explains terms only and gives no medical advice.

How to keep the terms apart

Exams mix the branches, the hormones and the time scales. Connect each term to one test.

Then test from the terms. Cover the right column and recall the test. Our guide to memorising psychology terminology explains why recall beats rereading for lists like this.

Psychology World is a dictionary app with more than 18,000 psychology terms. Search the dictionary for the terms in the table and save the ones you miss to one bookmark list. Then study the list as flashcards, as multiple-choice questions once it has four or more terms, or by typing each answer. The home page shows the four steps of the learning loop and what each study mode does.