Explain how the nervous system and endocrine system work together to bring about the 'fight or flight' response when an organism perceives a threat.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When an organism detects a threat, a rapid series of coordinated changes occur in the body that prepare it for either confronting or escaping the danger. These changes involve both electrical signalling and chemical signalling, and the two systems must act in a precise sequence to produce the full response.
Model answer (4 marks)
1. The sympathetic nervous system immediately sends a nerve impulse to the adrenal medulla.
2. The adrenal medulla releases adrenaline (epinephrine) into the bloodstream.
3. Adrenaline binds to β‑adrenergic receptors on target tissues, causing increased heart rate, bronchodilation, glycogenolysis, etc.
4. The nervous system gives a rapid, local signal; the endocrine system supplies a sustained, widespread hormonal effect, making the two systems complementary.
2. The adrenal medulla releases adrenaline (epinephrine) into the bloodstream.
3. Adrenaline binds to β‑adrenergic receptors on target tissues, causing increased heart rate, bronchodilation, glycogenolysis, etc.
4. The nervous system gives a rapid, local signal; the endocrine system supplies a sustained, widespread hormonal effect, making the two systems complementary.
Examiner tips
- Use the exact sequence: nervous system → adrenal medulla → adrenaline → receptors → physiological changes.
- Show the complementary roles of speed (nervous) and duration (endocrine).
Common mistakes
- Confusing the adrenal cortex with the medulla; only the medulla releases adrenaline.
- Omitting the role of adrenaline binding to receptors or the specific physiological changes.
Mark scheme (4 marks)
- The nervous system rapidly transmits a signal to the adrenal gland
- The adrenal medulla releases adrenaline into the blood
- Adrenaline binds to receptors on target cells, producing physiological changes
- The two systems are complementary because the nervous system provides speed whereas the endocrine system provides a sustained, widespread response
Key terms in this question
nervous system · endocrine system
Related
- All OCR A-Level Biology A (H420) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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