Simple structure of the ear, transmission processes.

The idea

The ear converts pressure variations in air into electrical signals in the auditory nerve. Sound waves enter the ear canal and strike the tympanic membrane, making it vibrate. These vibrations pass through the ossicles, the malleus, incus and stapes, which act as a lever system and impedance-matching device. The stapes pushes on the oval window of the fluid-filled cochlea, generating pressure waves in the cochlear fluid. These waves displace the basilar membrane, bending hair cells in the organ of Corti and triggering nerve impulses. The Eustachian tube equalises pressure on both sides of the tympanic membrane. Transmission therefore involves mechanical vibration, then fluid pressure waves, then electrochemical signalling.

What earns the marks

• Sound is a longitudinal pressure wave that enters the ear canal and causes the tympanic membrane to vibrate.
• The ossicles, malleus, incus and stapes, transmit and amplify vibrations from the tympanic membrane to the oval window.
• The oval window couples the vibrations into the fluid-filled cochlea, where pressure waves travel through the cochlear fluid.
• Movement of the basilar membrane bends hair cells in the organ of Corti, generating electrical impulses in the auditory nerve.
• The Eustachian tube connects the middle ear to the throat and equalises pressure across the tympanic membrane.
• The middle ear acts as an impedance-matching system, improving energy transfer from air to the fluid-filled inner ear.

Common mistakes and how to put them right

• Saying the ossicles amplify sound without explaining impedance matching.

  Put it right: The key idea is efficient transfer from air to fluid.

• Confusing the oval window with the round window or placing the cochlea in the middle ear.

  Put it right: The cochlea is part of the inner ear.

• Describing the ear as detecting transverse waves.

  Put it right: Sound in air is a longitudinal pressure wave.

• Omitting the role of hair cells and the auditory nerve, which converts mechanical movement into electrical signals.

Exam tips

• Draw a labelled flow diagram from ear canal to auditory nerve, naming each structure in order.
• Use the phrase pressure wave for sound and vibration for the tympanic membrane and ossicles.
• When asked about transmission, state the energy conversion at each stage: pressure to mechanical, mechanical to fluid pressure, fluid movement to electrical.
• Link the Eustachian tube to pressure equalisation rather than to hearing sensitivity.