The ear and hearing

Hearing is the sense by which the ear detects sound, which travels as vibrations in the air. The ear converts these vibrations into nerve signals that the brain interprets, a chain of mechanical and electrical events that animation can usefully trace from the outer ear inward. Anatomically the ear is divided into three regions: the outer ear, the middle ear and the inner ear.

The outer ear consists of the visible flap and the ear canal, which collect sound and funnel it toward the eardrum. Sound waves make the eardrum vibrate, and these vibrations pass into the middle ear, an air-filled cavity containing three tiny bones, the smallest in the body. The bones act as a lever system that amplifies the vibrations and transmits them to the inner ear. The inner ear contains the cochlea, a fluid-filled spiral structure lined with thousands of microscopic hair cells.

As the fluid in the cochlea moves, it bends these hair cells, which convert the mechanical movement into electrical impulses carried by the auditory nerve to the brain. Different regions of the cochlea respond to different frequencies, allowing the brain to distinguish high and low pitches. The inner ear also houses the vestibular system, a set of fluid-filled canals that sense head movement and help maintain balance, which is why ear problems can affect equilibrium as well as hearing.

Frequently asked questions

What are the three parts of the ear?

The outer ear collects sound, the middle ear amplifies and transmits the vibrations through three small bones, and the inner ear converts them into nerve signals.

How does the ear turn sound into signals the brain understands?

Sound vibrates the eardrum and middle-ear bones, which move fluid in the cochlea, bending hair cells that generate electrical impulses sent along the auditory nerve.

Why does the ear affect balance?

The inner ear contains the vestibular system, fluid-filled canals that detect head motion and help the body sense and maintain balance.