Corpus: Cochlea

The cochlea is a part of the inner ear that resembles the shape of a snail shell. It comprises the organ of Corti, the stria vascularis, as well as endolymph and perilymph. The cochlea is the seat of actual sound perception.

The bony cochlea consists of a spirally shaped tube, the cochlear canal (canalis spiralis cochleae), which winds around a conically shaped central axis, the modiolus cochleae. From the modiolus a thin bony ridge, the lamina spiralis ossea, which, with the membranes attached to it, divides the entire length of the spiral canal into three tubes:

• Scala vestibuli (vestibular staircase)
• Scala media (cochlear duct)
• Scala tympani (tympanic staircase)

The scala vestibuli is connected to the oval window (fenestra ovalis). It receives the sound pressure from the middle ear and guides it to the apex of the cochlearis, where the helicotrema is located.

At the helicotrema, the scala vestibuli merges in a sharp bend into the scala tympani, which runs parallel to the scala vestibuli in the opposite direction back to the round window (fenestra cochleae).

Between the two scalae lies the scala media (cochlear duct), which contains the organ of Corti. The scala media is separated from the scala vestibuli at the top by the Reissner membrane and from the scala tympani at the bottom by the basilar membrane. It is connected to the saccule at the base of the cochlea via the reunifying duct.

Pathological changes in the cochlea lead to sensorineural hearing loss. Mondini dysplasia is a congenital hypoplasia of the cochlea.

• Image source podcast: ©Magda Ehlers / Pexels