The spiral-shaped hearing organ of the inner ear. It converts mechanical sound vibrations into electrical nerve impulses that the brain interprets as sound.
Medical definition
The cochlea is a fluid-filled, snail-shaped bony structure in the inner ear. It contains three fluid compartments: the scala vestibuli (perilymph), scala tympani (perilymph), and scala media (endolymph). The organ of Corti sits within the scala media on the basilar membrane. It contains rows of inner and outer hair cells that detect fluid movement caused by sound vibrations. High-frequency sounds stimulate hair cells near the base; low-frequency sounds stimulate hair cells near the apex. The cochlear nerve transmits these signals to the auditory cortex via the cochlear nucleus and brainstem pathways.
Why it matters for vertigo
The cochlea and the vestibular apparatus share the same fluid-filled bony labyrinth and the same blood supply. This proximity is why ear diseases often affect both hearing and balance simultaneously. In Meniere disease, endolymphatic hydrops distends both cochlear and vestibular spaces, producing fluctuating hearing loss, tinnitus, and vertigo in the same attack. In labyrinthitis, inflammation involves both structures, distinguishing it from vestibular neuritis where the cochlea is spared. Sudden sensorineural hearing loss with vertigo is an ENT emergency because it suggests a vascular event in the labyrinthine artery supplying both structures.
Where I see this in clinic
Any patient with vertigo who also has hearing loss gets a different diagnostic pathway from me. BPPV does not affect the cochlea — hearing is always normal. Meniere disease, labyrinthitis, and acoustic neuroma all affect cochlear function. An audiogram is mandatory whenever vertigo is accompanied by hearing loss, tinnitus, or aural fullness. The audiogram tells me whether cochlear hair cells at the low-frequency end (Meniere pattern) or the high-frequency end (noise damage, presbycusis) are affected, which guides diagnosis before any vestibular test is done.
Related terms
Endolymph — the fluid inside the cochlea. Aural fullness — a cochlear symptom in Meniere disease. Tinnitus — often generated by cochlear damage. Hair cells — the sensory receptors inside the cochlea.
Medical Disclaimer: This glossary entry is for educational purposes only and is not a substitute for in-person clinical assessment. Consult Dr. Prateek Porwal directly. WhatsApp: 7393062200.