A student is investigating how the human ear processes sound. Explain how sound waves entering the outer ear are eventually converted into electrical impulses that the brain interprets as sound.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The human ear is a complex sensory organ. Sound travels as a longitudinal wave through air, entering the outer ear and travelling through several structures before a signal reaches the brain.
Model answer (5 marks)
Sound waves travel down the ear canal as a pressure wave of compressions and rarefactions.
The pressure waves strike the tympanic membrane, causing it to vibrate at the same frequency as the incoming sound.
The three ossicles – hammer (malleus), anvil (incus) and stirrup (stapes) – are linked to the eardrum and vibrate at the same frequency, amplifying the sound energy.
The stapes footplate transmits the vibrations into the fluid of the cochlea, where the motion of the basilar membrane moves the hair cells.
Each hair cell is tuned to a particular frequency; the hair cell that matches the incoming frequency opens ion channels, generating an electrical impulse that is carried by the auditory nerve to the brain, which interprets it as sound.
The pressure waves strike the tympanic membrane, causing it to vibrate at the same frequency as the incoming sound.
The three ossicles – hammer (malleus), anvil (incus) and stirrup (stapes) – are linked to the eardrum and vibrate at the same frequency, amplifying the sound energy.
The stapes footplate transmits the vibrations into the fluid of the cochlea, where the motion of the basilar membrane moves the hair cells.
Each hair cell is tuned to a particular frequency; the hair cell that matches the incoming frequency opens ion channels, generating an electrical impulse that is carried by the auditory nerve to the brain, which interprets it as sound.
Examiner tips
- Show the chain from ear canal to auditory nerve, using correct anatomical terms; include amplification by ossicles; mention frequency‑tuned hair cells; link to electrical impulse and brain interpretation
Common mistakes
- Confusing the role of the eardrum with the ossicles; not stating that hair cells are frequency‑selective; omitting the conversion of mechanical to electrical signal via ion channels.
Mark scheme (5 marks)
- Sound waves travel down the ear canal as a pressure wave / compressions and rarefactions
- The pressure waves cause the eardrum to vibrate at the same frequency as the incoming sound
- The small bones (hammer, anvil and stirrup) vibrate at the same frequency and amplify the sound waves
- Vibrations are transferred to fluid in the cochlea, causing small hairs to move, with each hair sensitive to a different frequency
- The hair sensitive to the incoming frequency triggers an electrical impulse via a nerve cell, which the brain interprets 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 →
More Astrophysics and cosmology questions
- A doctor uses ultrasound waves to scan a patient's abdomen. Explain how ultrasou…
- Engineers use ultrasound to check for cracks inside large metal components, such…
- A geologist uses seismic waves produced by an earthquake to investigate the stru…
- A ship uses sonar to map the depth of the ocean floor. Explain how sonar waves a…