Explain how the central nervous system coordinates a response when a person touches a hot surface, without involving a reflex arc.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student places their hand on a hot surface. Receptors in the skin detect the high temperature and send information to the central nervous system, which then coordinates a voluntary response.
Model answer (4 marks)
1. Receptors in the skin detect the high temperature.
2. The receptors generate electrical impulses that travel via afferent neurons to the spinal cord and brain.
3. The CNS (brain and spinal cord) receives the signals, processes the information and decides on a response.
4. The CNS sends efferent impulses to the hand muscles, causing the hand to be withdrawn from the hot surface.
2. The receptors generate electrical impulses that travel via afferent neurons to the spinal cord and brain.
3. The CNS (brain and spinal cord) receives the signals, processes the information and decides on a response.
4. The CNS sends efferent impulses to the hand muscles, causing the hand to be withdrawn from the hot surface.
Examiner tips
- Use the exact sequence: receptor → afferent → CNS → efferent → effector.
- Show the role of the CNS as a processing centre, not just a relay.
Common mistakes
- Confusing the CNS with the peripheral nervous system; forgetting to mention the brain/spinal cord as the processing site.
- Using vague terms like ‘body’ instead of ‘CNS’ or ‘effector’.
Mark scheme (4 marks)
- Receptors in the skin detect the stimulus (high temperature / heat)
- Electrical impulses / signals are sent to the central nervous system (brain and spinal cord)
- The CNS / brain acts as a coordination centre and processes the information
- The CNS sends impulses to an effector (muscle or gland) to bring about a response (e.g. pulling the hand away)
Related
- Revision notes: The human nervous system →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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