A student is investigating how the human ear detects different sounds. Explain how sound waves travelling through the ear canal are converted into electrical impulses that the brain can interpret as sound.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The human ear is a remarkable organ capable of detecting sounds across a wide range of frequencies. Sound enters the outer ear as a longitudinal wave, creating alternating compressions and rarefactions that travel through the ear canal before being processed by several structures inside the ear.
Model answer (5 marks)
Sound waves reaching the ear canal cause the eardrum to vibrate at the same frequency as the sound. The vibration is transmitted through the ossicles (hammer, anvil, stirrup), which amplify the motion and transfer it to the fluid of the cochlea. The fluid movement bends the hair cells that line the cochlear duct; each hair cell is tuned to a particular frequency. When a hair cell bends, ion channels open and an action potential is generated in the attached auditory nerve. The nerve carries the electrical impulse to the brain, where it is interpreted as sound.
Examiner tips
- Mention the eardrum, ossicles, cochlear fluid, hair cells and auditory nerve in the correct order.
- Show that each step occurs at the same frequency and that the ossicles amplify the motion.
- Use the term ‘action potential’ for the electrical impulse.
- Explain that different hair cells respond to different frequencies.”]
Mark scheme (5 marks)
- Sound waves cause the eardrum to vibrate at the same frequency as the incoming sound wave
- The small bones (hammer, anvil and stirrup) vibrate at the same frequency and amplify the sound waves
- The vibrations are transferred to fluid in the cochlea
- Small hairs lining the cochlea move in response to the fluid movement, with each hair sensitive to a different frequency
- The movement of a hair triggers an electrical impulse in the attached nerve cell, which is sent to the brain and interpreted as sound
Key terms in this question
Related
- All OCR A-Level Physics B: Advancing Physics (H557) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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