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Histology · Special senses

Inner ear: the cochlea and the organ of Corti !

  • Organ

The cochlea is a fluid-filled spiral tube. Inside it, the organ of Corti has hair cells that turn sound vibration into nerve signals.

Updated 2026-11-01

See it in 3D: Cochlea

What it is

The cochlea is the hearing part of the labyrinth: a bony canal coiled around a central core, the modiolus, which in section is divided into three compartments. The organ of Corti rests on the basilar membrane, with inner and outer hair cells covered by the tectorial membrane. Because human hair cells do not regenerate, their loss explains most sensorineural hearing loss.

Structure

  • Section of the cochlea: scala vestibuli on top, cochlear duct (scala media) in the middle and scala tympani below.
  • The vestibular (Reissner's) membrane separates the scala vestibuli from the cochlear duct; the basilar membrane separates it from the scala tympani.
  • The scala vestibuli and tympani hold perilymph (low in potassium); the cochlear duct holds endolymph, which is rich in potassium.
  • Stria vascularis: an epithelium on the outer wall of the cochlear duct with capillaries inside it, which is unusual; it makes the endolymph.
  • Organ of Corti: one row of inner hair cells and three rows of outer hair cells, held by supporting cells (pillar cells that form the tunnel of Corti, and phalangeal cells); the tectorial membrane lies on top.
  • Modiolus: the bony core that houses the spiral ganglion, with the bipolar neurons of the cochlear nerve.

Step by step

  1. The stapes vibrates in the oval window and moves the perilymph of the scala vestibuli.
  2. A travelling wave displaces the basilar membrane at a spot that depends on the frequency.
  3. Hair cells ride up and down with the basilar membrane and their stereocilia bend against the tectorial membrane.
  4. Bending toward the tallest stereocilium opens channels at the tips, potassium flows in from the endolymph and the cell depolarizes.
  5. The hair cell releases transmitter onto spiral ganglion fibres and the signal travels along the cochlear nerve.

Clinical notes

  • Presbycusis: gradual loss of hair cells that starts at the base of the cochlea, so high pitches go first.
  • Loud noise and some ototoxic drugs, such as aminoglycosides, mainly damage the outer hair cells.
  • Ménière disease: endolymphatic hydrops causes attacks of vertigo, fluctuating hearing loss, tinnitus and a feeling of ear fullness.

Test yourself

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

Which membrane separates the cochlear duct from the scala tympani?

The basilar membrane, on which the organ of Corti sits.

Which structure produces endolymph?

The stria vascularis, on the outer wall of the cochlear duct.

Why are high pitches lost first in presbycusis?

Hair cell damage begins at the base of the cochlea, the region that responds to high frequencies.

Which cells of the organ of Corti amplify vibration and produce otoacoustic emissions?

The outer hair cells.

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Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.

Sources: 14.1 Sensory Perception (OpenStax, Anatomy and Physiology 2e, 2022); How Do We Hear? (National Institute on Deafness and Other Communication Disorders (NIDCD), 2026).

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