Outer hair cells on a human organ of Corti (about X5000). In this area there are only three rows, but in some regions there are four and even five rows. Stimulating these cells will cause the nerve to fire and hearing to take place.

Anatomically the three (four) rows of outer hair cells lie on the outer curve of the Organ of Corti on the spiral basilar membrane. The single row of inner hair cells lie in a tighter spiral closer to the centre of the cochlea. The outer hair cells are responsible for hearing up to about 75dB and are closer to the tip of the tectorial membrane. The inner hair cells are not as easily stimulated and are therefore more impervious to noise damage. Hence noise induced hearing loss rarely exceeds 75 to 80db. (See the cochlea picture).