A sprinter is waiting for the starting pistol to fire at the beginning of a race. When the sound reaches the sprinter's ears, a nerve impulse travels to the brain, which then sends signals to the muscles in the legs. Explain how the nervous system coordinates the sprinter's response to the starting pistol.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A sprinter crouches at the start line, listening carefully for the starting pistol. The moment the pistol fires, the sprinter's legs push powerfully off the blocks.
Model answer (5 marks)
The ear is the receptor that detects the sound of the pistol and converts it into a nerve impulse.
1. The auditory receptor cells in the cochlea transduce the sound waves into an electrical signal.
2. The signal is carried by sensory neurons through the auditory nerve to the brain.
3. In the brain, the central nervous system processes the information and generates a motor command.
4. Motor neurons then conduct the impulse from the brain to the leg muscles.
5. The muscles contract, producing the sprinter’s powerful push off the blocks.
1. The auditory receptor cells in the cochlea transduce the sound waves into an electrical signal.
2. The signal is carried by sensory neurons through the auditory nerve to the brain.
3. In the brain, the central nervous system processes the information and generates a motor command.
4. Motor neurons then conduct the impulse from the brain to the leg muscles.
5. The muscles contract, producing the sprinter’s powerful push off the blocks.
Examiner tips
- Use the term ‘receptor’ for the ear, ‘sensory neuron’ for the afferent pathway, and ‘motor neuron’ for the efferent pathway.
- Show the sequence: receptor → sensory neuron → CNS → motor neuron → effector.
- Mention that the CNS processes the signal and coordinates the response.
- Use the word ‘contract’ for the muscle response.
Common mistakes
- Confusing the ear with the brain as the receptor.
- Using ‘nerve impulse’ for both sensory and motor pathways without distinction.
- Omitting the role of the CNS in processing the signal.
Mark scheme (5 marks)
- The ear acts as a receptor, detecting the stimulus (sound of the pistol)
- A nerve impulse / electrical signal is sent along sensory neurones to the brain / central nervous system (CNS)
- The brain (CNS) processes the information and coordinates a response
- A nerve impulse is sent along motor neurones from the brain / CNS to the muscles (effectors)
- The muscles (effectors) contract / respond, causing movement
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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