The ear and hearing

The ear is the organ of hearing and balance. It is divided into three parts: the outer ear, the middle ear and the inner ear. The outer ear consists of the visible flap, called the pinna or auricle, and the ear canal that leads inward. Its shape helps collect sound waves and channel them toward the eardrum, a thin membrane that vibrates in response to the changing air pressure of a sound.

Behind the eardrum lies the air-filled middle ear, which contains three of the smallest bones in the body, often known as the hammer, anvil and stirrup. These bones, linked in a chain, transmit the eardrum's vibrations across the middle ear and amplify them. The chain ends at a second membrane covering an opening into the inner ear. A narrow passage called the Eustachian tube connects the middle ear to the back of the throat and equalises air pressure on the two sides of the eardrum.

The inner ear contains the cochlea, a coiled, fluid-filled structure lined with thousands of tiny hair cells. Vibrations passed into the cochlear fluid bend these hair cells, which convert the motion into nerve impulses. The impulses travel along the auditory nerve to the brain, where they are interpreted as sound, with different regions of the cochlea responding to different pitches. Alongside the cochlea, the inner ear holds the vestibular system — a set of fluid-filled canals and chambers that sense head movement and gravity and so provide the sense of balance.

Frequently asked questions

What does the eardrum do?

The eardrum is a thin membrane that vibrates when sound waves reach it, passing those vibrations to the small bones of the middle ear.

What is the cochlea?

The cochlea is the coiled, fluid-filled part of the inner ear lined with hair cells that turn sound vibrations into nerve signals sent to the brain.

How does the ear help with balance?

The inner ear contains the vestibular system, a set of fluid-filled canals that detect head movement and the pull of gravity, contributing to balance.