Hearing in Stereo

What am I looking at?

This image shows the tips of multiple stereocilia (1), which extend from hair cells in your inner ear. You can also see the connections (2) between one stereocilium and another; these act as motion detectors for the cells. The inset image is a magnification of one of these connections; the yellow dots (3) represent proteins that aid in detecting the movement of the stereocilia.

Biology in the background

The inner ear is composed of a series of different structures that turn sound waves from the environment into a neuronal signal that can be interpreted by the brain. Sound is essentially pressure waves that travel through the air. When these pressure waves hit our eardrums, they cause the eardrum to vibrate. This vibration travels through several very small bones in the inner ear, passing the signal along to the cochlea – a spiral-shaped, fluid-filled organ containing cells that can detect these vibrations.

When the vibrations hit the cochlea, they cause the fluid inside it to move, mimicking the sound waves in the air outside the ear. The movement of the fluid in the cochlea moves tiny projections – the stereocilia – that extend from the hair cells lining the inner surface of the cochlea. In fact, hair cells got their name from stereocilia, because the way the stereocilia extend from the hair cells’ tops makes it look like they have hair. Each stereocilium is connected to those around it by several different kinds of links, one of which is called a tip link (2).

Any movement of the stereocilia causes the tip links to either stretch or relax. This stretching and relaxing is detected by proteins embedded in the link (3). These proteins translate this mechanical movement into a molecular signal inside the hair cell. The hair cell then passes that signal to neurons in the auditory nerves, which communicate the information to the hearing centers of the brain.

Technique  

This image was created using scanning electron microscopy.