Britannica Sources used in this answer

How does the basilar membrane help the ear distinguish pitch?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Acoustics — acoustics Artificial omni-directional sound source in an anechoic acoustic chamber.

The basilar membrane distinguishes pitch through a process known as "place theory," which relies on the membrane's physical properties that change along its length.1

As the basilar membrane extends from the base of the cochlea to its apex, it undergoes continuous structural changes: it increases in width and mass while decreasing in stiffness. Because of these variations, different regions of the membrane are tuned to vibrate most vigorously in response to specific sound frequencies.12

High-frequency sounds cause the stiffer, narrower basal end of the membrane to vibrate.12
Low-frequency sounds cause the more flexible, wider apical end to vibrate.12

When a sound wave enters the cochlea, it travels along the membrane until it reaches the region corresponding to its frequency, where the vibration peaks. This peak stimulation activates the hair cells in the organ of Corti at that specific location, sending nerve impulses to the brain. The brain identifies the pitch based on which group of nerve fibers is activated.1