Cochlea

Nerves

Open in 3D

The cochlea is the hearing part of the inner ear: a bony tube coiled about two and a half turns round a central core (the modiolus), about 9 mm across and 5 mm high, deep in the petrous part of the temporal bone. Inside, it is split along its length into three fluid-filled channels. The stapes rocks in the oval window and sends pressure waves through the fluid; they run along the basilar membrane, which is narrow and stiff at the base and wide and floppy at the tip, so high notes peak near the base and low notes near the tip. About 3,500 inner hair cells in the organ of Corti turn that movement into nerve signals, carried to the brain by the cochlear nerve. The round window, a membrane at the start of the basal turn, bulges out to let the fluid move. This model is a simplified shape built from textbook measurements.