There are three rows of outer hair cells (OHCs) numbering about 12000 hairs. The upper end of each hair has tiny protruding hairs that are relatively stiff. These are called stereocilia.

OHCs put pressure on the tectorial membrane to respond to commands from the brain. The OHCs are able to fine-tune the cochlea for frequency discrimination. When hyperpolarized, the OHC increases in length up to 5% due to the protein prestin. Depolarization causes the OHCs to shorted. Modulating the stiffness of the basilar membrane can lead to better tuning and more pronounced amplification. They are able to change their lengthand can send messages to IHCs.