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Inner ear: cochlea, vestibule and semicircular canals in the clinic

  • Applied anatomy

The inner ear turns sound into nerve signals in the cochlea and senses head movement in the vestibule and semicircular canals.

Updated

See it in 3D: Cochlea · Vestibule · Semicircular canals · Vestibulocochlear nerve (VIII)

What it is

The inner ear is a fluid-filled labyrinth in the temporal bone with two jobs. The cochlea converts sound waves into nerve impulses; the vestibule (utricle and saccule) and the three semicircular canals sense gravity, linear and rotational movement. Both send signals through the vestibulocochlear nerve (VIII). Disease here produces sensorineural hearing loss, tinnitus and vertigo, often together, which is why the clinic treats hearing and balance as one organ.

Applied anatomy

  • Bony labyrinth filled with perilymph; inside it, the membranous labyrinth filled with endolymph.
  • Cochlea: about two and three-quarter turns; scala vestibuli (from the oval window), cochlear duct (scala media) with the organ of Corti, and scala tympani (ends at the round window).
  • Organ of Corti on the basilar membrane: one row of inner hair cells and three rows of outer hair cells, stereocilia touching the tectorial membrane.
  • Vestibule: utricle and saccule, each with a macula whose otolithic membrane is weighted by calcium carbonate crystals.
  • Three semicircular canals (one horizontal, two vertical) at right angles, each with an ampulla and a cupula.
  • Vestibulocochlear nerve (VIII): carries cochlear and vestibular signals through the internal acoustic meatus to the brainstem and cerebellum.

Clinical physiology

  • The stapes moves the oval window, a travelling wave runs along the basilar membrane and bending stereocilia open ion channels: sound becomes an electrical signal.
  • Head rotation makes canal fluid lag and deflect the cupula; tilting or accelerating shifts the otolithic membrane.

Clinical correlation

  • Sensorineural hearing loss means damage to the cochlea or nerve; the Weber test lateralises to the better ear.
  • Ménière disease: attacks of vertigo lasting minutes to hours with fluctuating low-to-mid frequency hearing loss, tinnitus and ear fullness, usually one ear.
  • Labyrinthitis (vertigo with hearing loss) involves the labyrinth; vestibular neuritis affects only the vestibular nerve, so hearing is spared.
  • Unilateral sensorineural loss or tinnitus needs a lesion of the nerve (for example a vestibular schwannoma) ruled out.
  • Ototoxic drugs (aminoglycosides, platinum chemotherapy) damage hair cells: hearing and balance can both be lost.

Next step / Initial management

  • Examine with tuning forks (Rinne, Weber) and a bedside vestibular exam; confirm with pure-tone audiometry.
  • Sudden sensorineural hearing loss is an emergency: same-day referral for audiometry and early corticosteroids.
  • Recurrent vertigo with hearing loss (possible Ménière): salt restriction and drugs for attacks while awaiting routine ENT referral and audiometry.
  • Unilateral or asymmetric sensorineural loss, or unilateral tinnitus: refer to ENT for audiometry and MRI of the internal auditory canals.
  • Patients on ototoxic drugs: baseline and follow-up audiometry; refer if hearing or balance changes.

Test yourself

Think of the answer, then tap the question to see it.

Why does noise-induced or age-related hearing loss affect high frequencies first?

High frequencies are detected at the base of the cochlea, the region most exposed and damaged first; low tones are detected towards the apex.

A newborn passes otoacoustic emissions. Which cells did this test check?

The outer hair cells of the cochlea, whose amplifying activity produces the emissions; it does not test the auditory nerve or brainstem.

A patient has attacks of vertigo for hours, fluctuating hearing loss, tinnitus and ear fullness. What inner ear change is linked to this?

Endolymphatic hydrops, a build-up of endolymph in the membranous labyrinth, as in Ménière disease.

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Educational content; it does not replace a medical assessment and is not a clinical instruction. For a real case, follow current guidelines and specialist advice.

Sources: Inner Ear Anatomy and Cochlear Physiology (StatPearls (NCBI Bookshelf), 2026); How Do We Hear? (National Institute on Deafness and Other Communication Disorders (NIDCD), NIH, 2022); Balance Disorders (National Institute on Deafness and Other Communication Disorders (NIDCD), NIH, 2018); Ménière's Disease (National Institute on Deafness and Other Communication Disorders (NIDCD), NIH, 2024).

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