Audition Promenade round Cochlea autour Cochlée oreille ear organ of Corti oreille ear CRIC Montpellier Remy Pujol U254

	Cochlea
	Overview / Physics / Fluids / Stria
	Drawings: S. Blatrix; Pictures: M. Lavigne-Rebillard, M. Lenoir

The cochlea is the peripheral auditory organ of the inner ear. Its name comes from its spiral structure mimicking a marine snail.

Cochlea from a human fetus ( 5 months of gestation)
	The bony capsule has been dissected out, showing the 2 1/2 coils of the membranous labyrinth (35 mm in length). The oval (blue arrow) and round (yellow arrow) windows are indicated. scale bar: 0.5 mm

M. Lavigne-Rebillard

**Cross section of the whole cochlea**
	Plan of cross section
	This mid-modiolar section shows the coiling of the cochlear duct (1) which contains endolymph, and the scala vestibuli (2) and scala tympani (3) which contain perilymph. The red arrow is from the oval window, the blue arrow points to the round window. Within the modiolus, the spiral ganglion (4) and auditory nerve fibres (5) are seen. For details, see the single turn cross section below.

**Cross section of one single turn of the cochlea**

The cochlear duct (1) is isolated from the scala vestibuli (2) and scala tympani (3) by Reissner's (4) and basilar (5) membranes respectively. The organ of Corti is covered by the tectorial membrane (6) floating in the endolymph. The stria vascularis (7) and the fibres (8) going to the spiral ganglion through the bony spiral lamina (9) are also shown.

View of a rat cochlear spiral
(Scanning electron microscopy)

In the rat, the basilar membrane develops a 3 turn spiral of a total length of 22 mm (compare with the coiling in human).

Only the extreme basal part (the hook) is not seen.

scale bar: 2 mm

Note that the bony capsule, stria and tectorial membrane have been removed

M. Lenoir