[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) › Cochlea [Sense organs](https://durgical.com/en/anatomy/system/sense-organs/) · [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) # Cochlea The cochlea is the snail-shaped, fluid-filled spiral of the inner ear; it turns sound waves into nerve signals, and a cochlear implant sits inside it. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=head_neck&select=cochlea&side=r) Opens in the Durgical app, no sign-up needed. ## What it is A snail-shaped spiral of fluid-filled tubes in the inner ear. ## What it does Turns sound waves into nerve signals; a cochlear implant sits inside it. ## Key points - Three spaces: scala vestibuli and scala tympani hold perilymph and meet at the apex (helicotrema); the cochlear duct between them holds potassium-rich endolymph and the organ of Corti - Inner hair cells send most of the signal to the brain; outer hair cells amplify it and produce otoacoustic emissions, the basis of newborn hearing screening - Noise-induced hearing loss: a notch near 4 kHz on the audiogram; presbycusis: bilateral, symmetric loss of high frequencies, starting at the base of the cochlea - Unilateral or asymmetric sensorineural loss needs imaging to exclude a vestibular schwannoma ## Key facts **Where** Inner ear, petrous [temporal bone](https://durgical.com/en/anatomy/temporal-bone/); 2.5 turns **Blood supply** Labyrinthine artery (AICA/basilar) **Nerve** Cochlear part of VIII **Function** Hearing (organ of Corti); base = high pitch, apex = low ## Relations **Contents** Bony spiral around a central [axis](https://durgical.com/en/anatomy/axis/) (modiolus) that holds the spiral ganglion; scala vestibuli, cochlear duct with the organ of Corti on the basilar membrane, and scala tympani **Lateral** Middle ear: the basal turn bulges as the promontory; the oval window ([stapes](https://durgical.com/en/anatomy/stapes/) footplate) above it opens to the vestibule and the round window closes the scala tympani **Behind** Vestibule and [semicircular canals](https://durgical.com/en/anatomy/semicircular-canals/), the rest of the bony labyrinth **Medial** Fundus of the [internal acoustic meatus](https://durgical.com/en/anatomy/internal-acoustic-meatus/), where cochlear nerve fibres leave through its anteroinferior part **In front** [Carotid canal](https://durgical.com/en/anatomy/carotid-canal/) with the [internal carotid artery](https://durgical.com/en/anatomy/internal-carotid-artery/), close by in the petrous bone ## How to find it Deep in the petrous part of the temporal bone and cannot be examined directly. It is reached through the middle ear: the promontory and round window niche are seen once the [eardrum](https://durgical.com/en/anatomy/tympanic-membrane/) is lifted, and a cochlear implant electrode is passed through the round window into the scala tympani. ## Examination - Rinne positive (air louder than bone) in both ears and Weber lateralising to the better ear: sensorineural loss - Pure-tone audiometry: air and bone conduction thresholds drop together with no air-bone gap - Otoacoustic emissions: absent when outer hair cells are damaged; used to screen newborns ## On imaging CT of the temporal bone shows the bony cochlea (two and a half turns), malformations and the lucent ring of cochlear otosclerosis; high-resolution T2-weighted MRI shows the fluid inside it and the cochlear nerve, and confirms the cochlea is open before an implant. ## Common problems - Age-related and noise-induced hearing loss: the sensory hair cells wear out. - Sudden sensorineural hearing loss: an emergency. - Tinnitus (ringing). ## How it is diagnosed Audiometry; MRI if one side is affected. ## Treatment - Hearing protection; hearing aids. - Urgent steroids for sudden hearing loss. - Cochlear implant for severe to profound loss. ## Clinical notes - Cochlear implant: an electrode array in the scala tympani stimulates the spiral ganglion directly, bypassing lost hair cells; it needs an intact cochlear nerve - After bacterial meningitis the cochlea can fill with bone (labyrinthitis ossificans); hearing is checked early so an implant can be placed before it closes - Ototoxic drugs such as aminoglycosides and cisplatin damage outer hair cells, high frequencies first - Ménière disease: excess endolymph (hydrops) with episodic vertigo, fluctuating low-frequency hearing loss, tinnitus and aural fullness ## Development The membranous labyrinth grows from the otic placode (ectoderm) via the otic vesicle; the surrounding otic capsule ossifies into the bony labyrinth, adult-sized at birth. ## Memory aid Endolymph is like the inside of a cell (high potassium); perilymph is like plasma or CSF (high sodium). ## Related conditions - [Ménière disease](https://durgical.com/en/conditions/meniere-disease/) - [Presbycusis (age-related hearing loss)](https://durgical.com/en/conditions/presbycusis/) - [Hearing loss (conductive and sensorineural, including sudden hearing loss)](https://durgical.com/en/conditions/hearing-loss/) - [Otosclerosis](https://durgical.com/en/conditions/otosclerosis/) ## Test yourself Think of the answer, then tap the question to see it. ## What are the three spaces of the cochlea and their fluids? Scala vestibuli and scala tympani hold perilymph and meet at the helicotrema; the cochlear duct between them holds potassium-rich endolymph and the organ of Corti. ## What do otoacoustic emissions test, and where are they used? Outer hair cell function in the cochlea; they are the basis of newborn hearing screening. ## What audiogram patterns are typical of noise-induced hearing loss and presbycusis? Noise: a notch near 4 kHz; presbycusis: bilateral, symmetric high-frequency loss starting at the base of the cochlea. ## Why does unilateral or asymmetric sensorineural hearing loss need imaging? To exclude a vestibular schwannoma. ## Where is a cochlear implant electrode placed, and what does it require? In the scala tympani, via the round window; it stimulates the spiral ganglion directly and needs an intact cochlear nerve. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/anatomy/cochlea/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** cochlea TA2 6964 **Official Spanish (DeCS)** Cóclea DeCS D003051 **English (TA2)** Cochlea ## Related - [Vestibule](https://durgical.com/en/anatomy/vestibule/) - [Vestibulocochlear nerve (VIII)](https://durgical.com/en/anatomy/vestibulocochlear-nerve/) - [Temporal bones](https://durgical.com/en/anatomy/temporal-bone/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=3080); [Inner Ear Anatomy and Cochlear Physiology](https://www.ncbi.nlm.nih.gov/books/NBK538335/); [Neuroanatomy, Cranial Nerve 8 (Vestibulocochlear)](https://www.ncbi.nlm.nih.gov/books/NBK537359/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/cochlea/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/cochlea/