Fight-or-flight response

The fight-or-flight response is a rapid set of bodily changes triggered by perceived danger, preparing an organism to confront a threat or escape it.

Sympathetic nervous system: A division of the autonomic nervous system that mobilizes bodily activity during stress and exertion. Its nerve signals drive many immediate changes in the response.
Autonomic nervous system: The nervous system division that regulates involuntary functions such as heartbeat, digestion, and breathing. The response is a rapid mobilization within this broader control system.
Freeze response: A defensive reaction involving immobility or reduced movement when danger is perceived. Freezing is another possible defensive response, rather than the confrontation or escape emphasized here.
Pupil dilation: An increase in the diameter of the pupil, allowing more light to enter the eye. It is one visible change associated with sympathetic arousal.
Adrenaline: A hormone and neurotransmitter that increases cardiovascular output and mobilizes energy during acute stress. Its release helps produce the response’s rapid changes in heart rate and energy availability.
Amygdala: A set of brain nuclei involved in processing emotionally significant stimuli, including potential threats. Threat appraisal involving the amygdala can help initiate the response.
Tend-and-befriend: A proposed stress response involving social affiliation and caregiving under threat. It describes affiliative coping that the fight-or-flight model does not foreground.
Glycogenolysis: The breakdown of glycogen into glucose or glucose-1-phosphate. Mobilizing stored carbohydrate helps make fuel available during acute exertion.
Hypothalamus: A brain region that regulates homeostasis and coordinates autonomic and endocrine responses. It links threat-related brain processing to bodily stress responses.
Threat perception: The interpretation of a stimulus or situation as potentially harmful. The response begins when danger is perceived, not only when harm is objectively present.

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