A to Z of the Fight or Flight Response

Fight-or-Flight Response

The fight-or-flight response, also called the hyperarousal or acute stress response, is the body’s rapid reaction to a perceived threat. It prepares a person to confront danger or escape by shifting the body’s activity and energy toward immediate physical action.

The Four Stages

1. Sensory perception

   • The eyes, ears, nose, tongue, and/or sense of touch detect information about the surroundings.
   • Specialized cells convert sensory information into electrical signals.
   • Neurons carry those signals to the brain.

2. Brain processing

   • The thalamus receives and relays sensory information for processing.
   • The amygdala assesses emotional significance, including whether the situation may involve fear or danger.
   • The amygdala passes information to the hypothalamus, which helps control the sympathetic nervous system and endocrine system.
   • The hypothalamus releases corticotropin-releasing hormone (CRH), signaling the pituitary gland, and activates the sympathetic nervous system.

3. Messages sent to the body

   • The anterior pituitary releases adrenocorticotropic hormone (ACTH) into the bloodstream. ACTH stimulates the adrenal cortex to release cortisol.
   • At the same time, the sympathetic nervous system signals the adrenal medulla to release adrenaline.

4. Physiological response

   • Adrenaline prompts the liver to convert glycogen into glucose, making more energy available to skeletal muscles.
   • The heart beats faster, increasing cardiac output and helping deliver glucose, oxygen, and nutrients to muscles.
   • Breathing rate increases, raising oxygen intake and speeding the removal of carbon dioxide.
   • Blood vessels to skeletal muscles widen, while vessels supplying the digestive system narrow, redirecting resources toward immediate action.
   • Pupils dilate; the video also mentions tunnel vision and reduced hearing.

These changes occur quickly and support physical exertion. When the threat passes, the body returns to a calmer state and restores internal balance, or homeostasis.

Speakers and Sources Featured

• Speaker: One unnamed narrator provides the explanation.
• Other speakers: None are identifiable in the subtitles.
• The narration refers to sensory organs, brain structures, the sympathetic nervous system, the endocrine system, and adrenal hormones as part of its explanation.