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Psychology & Neuroscience
Stress and the Nervous System
Fight-or-flight, cortisol, and the stress response
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Stress is the body and mind's response to a challenge, threat, or demand. It matters because the same systems that help a person react quickly in danger can also affect sleep, mood, attention, digestion, and health when activated too often. The nervous system detects possible danger and rapidly coordinates changes in the brain and body. Understanding this response helps students connect psychology, biology, and everyday behavior.
Key Facts
- The sympathetic nervous system prepares the body for action by increasing heart rate, breathing rate, and glucose release.
- The parasympathetic nervous system helps return the body toward rest by slowing heart rate and supporting digestion.
- The HPA axis pathway is hypothalamus to pituitary gland to adrenal glands.
- Adrenal glands release epinephrine quickly and cortisol more slowly during stress.
- Stress response = threat appraisal + body activation + coping behavior.
- Allostatic load means the wear and tear caused by repeated or long-lasting stress responses.
Vocabulary
- Sympathetic nervous system
- The branch of the autonomic nervous system that activates the body for fight, flight, or focused effort.
- Parasympathetic nervous system
- The branch of the autonomic nervous system that helps the body conserve energy, recover, and digest food.
- HPA axis
- A hormone pathway linking the hypothalamus, pituitary gland, and adrenal glands during stress.
- Cortisol
- A stress hormone released by the adrenal glands that helps mobilize energy and regulate longer stress responses.
- Fight-or-flight response
- A rapid stress reaction that prepares the body to confront a threat or escape from it.
Common Mistakes to Avoid
- Thinking all stress is harmful, which is wrong because short-term stress can improve alertness and performance when recovery follows.
- Confusing the sympathetic and parasympathetic systems, which is wrong because sympathetic activation speeds the body up while parasympathetic activation supports calming and recovery.
- Assuming cortisol and epinephrine do the same job, which is wrong because epinephrine acts quickly for immediate arousal while cortisol helps sustain energy availability over a longer time.
- Ignoring the role of perception, which is wrong because the brain's appraisal of an event strongly affects whether the body treats it as a stressor.
Practice Questions
- 1 A student's resting heart rate is 72 beats per minute. During a stressful exam, it rises to 108 beats per minute. What is the increase in beats per minute, and what percent increase is this from rest?
- 2 A person takes 12 breaths per minute while relaxed and 24 breaths per minute during acute stress. If the stressful period lasts 5 minutes, how many extra breaths occur compared with the relaxed rate?
- 3 Explain why chronic stress can affect digestion, sleep, and concentration even when there is no immediate physical danger.