Explain how the nervous system and endocrine system work together to produce the 'fight or flight' response when a person perceives a threat.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When an organism detects a sudden threat in its environment, a rapid, coordinated response is initiated that prepares the body for intense physical activity. This response involves both rapid nerve impulses and slower-acting chemical signals.
Model answer (4 marks)
The hypothalamus, as part of the brain, detects the threat and immediately activates the sympathetic nervous system. Rapid nerve impulses travel through the sympathetic fibres to the adrenal medulla, signalling it to release adrenaline into the bloodstream. The released adrenaline binds to adrenergic receptors on target organs (heart, lungs, liver, muscles), producing physiological changes such as increased heart rate, bronchodilation, glycogenolysis and mobilisation of energy stores. Thus the nervous system provides the fast, initial signal, while the endocrine system sustains the response through adrenaline, showing clear coordination between the two systems.
Examiner tips
- Mention the hypothalamus and sympathetic nerves first to show the rapid signal.
- State that adrenaline is released from the adrenal medulla and acts on target organs.
- Explain the physiological effects of adrenaline.
- Show the division of labour: nervous system = rapid, endocrine = sustained.
Common mistakes
- Confusing the adrenal cortex with the adrenal medulla.
- Omitting the role of the hypothalamus.
- Failing to list the specific physiological changes caused by adrenaline.
Mark scheme (4 marks)
- The hypothalamus or sympathetic nervous system sends nerve impulses to the adrenal medulla
- The adrenal medulla releases adrenaline into the blood
- Adrenaline binds to receptors on target organs, causing physiological changes that prepare the body for action
- This demonstrates coordination between the two systems: the nervous system provides rapid initial signalling while the endocrine system provides a sustained response via adrenaline
Key terms in this question
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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