CorpusHuman Anatomy
Special SensesDuct

Cochlear duct (scala media)

Ductus cochlearis

Also known as: scala media, Reissner membrane, vestibular membrane, stria vascularis, spiral ligament

The triangular, endolymph-filled spiral tube of the membranous labyrinth between the scala vestibuli and scala tympani; it houses the spiral organ on its floor and the stria vascularis on its outer wall.

Show on body map Ear — Coronal Section

Overview

In cross-section the cochlear duct is triangular. Its roof is the thin vestibular (Reissner) membrane (two cell layers), separating it from the scala vestibuli. Its floor is the basilar membrane (with the osseous spiral lamina), on which the spiral organ of Corti sits; the spiral limbus at the inner angle gives origin to the tectorial membrane. Its outer wall is formed by the spiral ligament (thickened periosteum) covered by the stria vascularis, a unique vascularised stratified epithelium (marginal, intermediate and basal cells) that secretes endolymph and generates the endocochlear potential.

The duct begins at the base as a blind cecum (vestibular cecum), connected to the saccule by the ductus reuniens, and ends at the apex as the cupular cecum. It is ≈32–35 mm long.

The intermediate cells of the stria vascularis are melanocytes derived from neural crest — explaining why pigmentary disorders such as Waardenburg syndrome cause deafness.

Location

Within the bony cochlear canal, attached to the osseous spiral lamina medially and the spiral ligament laterally.

Parts & subdivisions

  1. Vestibular (Reissner) membrane
    Roof; separates endolymph from scala vestibuli perilymph; bulges in Ménière disease.
  2. Basilar membrane
    Floor; supports the organ of Corti.
  3. Stria vascularis
    Outer wall; secretes K⁺ into endolymph; generates the +80 mV endocochlear potential.
  4. Spiral ligament
    Fibrous thickening anchoring the basilar membrane laterally; fibrocytes recycle K⁺.
  5. Spiral organ (of Corti)
    Sensory epithelium on the basilar membrane.
  6. Tectorial membrane
    Gelatinous flap from the spiral limbus overlying the hair cells.

Anatomy

Histology

Reissner membrane: squamous epithelium + mesothelium. Stria vascularis: marginal (epithelial), intermediate (melanocyte) and basal cells with an intraepithelial capillary network — the only vascularised epithelium in the body.

Function

  • Contain endolymph and the spiral organ
  • Generate and maintain the endocochlear potential (stria vascularis)
  • Form the cochlear partition that vibrates with sound

Clinical significance

Strial presbycusis

Atrophy of the stria vascularis with age lowers the endocochlear potential, producing a flat (all-frequency) sensorineural loss with good speech discrimination.

Ménière disease

Distension of the cochlear duct with bulging of Reissner membrane into the scala vestibuli; ruptures may mix endolymph and perilymph, poisoning hair cells (theory of acute attacks).

Test yourself

Which of the following correctly describes endolymph?
  1. High Na⁺, low K⁺, resembles CSF
  2. Fills the scala vestibuli and scala tympani
  3. High K⁺, low Na⁺, secreted by the stria vascularis
  4. Drains through the cochlear aqueduct into the subarachnoid space

Answer: High K⁺, low Na⁺, secreted by the stria vascularis

Endolymph (K⁺ ≈150, Na⁺ ≈1 mmol/L) fills the membranous labyrinth including the scala media; the stria vascularis secretes it and generates the +80 mV endocochlear potential. Perilymph (high Na⁺) fills the scala vestibuli and tympani and communicates with CSF.

More special senses questions

Compiled from standard anatomy and physiology references — see the Special Senses sources. For education only; not medical advice.