Read the following and answer the questions that follow:
Rahul was studying late at night when he accidentally placed his hand on a hot soldering iron. He instantly pulled his hand away before he even registered the pain consciously. His mother noticed this and asked him to explain the mechanism behind such a rapid response.
(a) Name the type of action described above and state which part of the central nervous system coordinates it. (1 mark)
(b) Trace the complete pathway of the nerve signal from the moment Rahul's hand touches the hot iron to the moment his hand is withdrawn. (2 marks)
(c) Even though the spinal cord coordinates this response, Rahul still feels the pain a moment later. Explain why. (1 mark)
Generated by claude-sonnet-4-6 · 2026-06-26 01:02 · grounding rag
Model Answer
(a) The action described is a reflex action. It is coordinated by the spinal cord (part of the central nervous system).
(b) Pathway of the nerve signal:
Hot iron → Receptor (skin) → Sensory neuron → Spinal cord (relay neuron forms reflex arc) → Motor neuron → Effector (muscle of hand) → Hand is withdrawn
The impulse travels from the dendritic tip of the sensory neuron to the cell body, along the axon, crosses the synapse via chemicals, and reaches the next neuron, finally reaching the muscle.
(c) Although the spinal cord coordinates the reflex action, the sensory information also travels upward to the brain simultaneously. The brain receives and processes this signal a moment later, which is when Rahul consciously feels the pain.
Source: Chapter 6, Section 6.1.1 — Reflex Actions
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Explanation
- (a) Always name both — the type of action (reflex) AND the coordinating part (spinal cord). Missing either loses the mark.
- (b) Examiners expect a clear, sequential pathway with all components: receptor → sensory neuron → spinal cord → motor neuron → effector. Mention of synapse/relay neuron adds accuracy.
- (c) The key phrase from the textbook is: "the information input also goes on to reach the brain" — this explains the delayed conscious perception of pain. Make sure to say the signal reaches the brain after the reflex is already complete.