Inner ear

Fluid systems of the labyrinth
- Membranous labyrinth
  - Filled with K-rich endolymph
  - Contains hair cells
  - Divided into vestibule and cochlear duct
- Bony labyrinth
  - Contains membranous labyrinth in Na-rich perilymph
  - Three cavities
    - Scala media (cochlear duct)
      - Filled with endolymph
      - Basilar membrane forms the floor of it
    - Scala vestibuli
      - Filled with perilymph
      - Above and separated from scala media
      - Connected to scala tympani at helicotrema
    - Scala tympani
      - Filled with perilymph
      - Below and separated from scala media
      - Runs downward from helicotrema to the round window
- Oval window vibrates -> sound waves transmitted in perilymph in scala vestibuli
  - -> sound waves vibrate the vestibular membrane and basilar membrane, thus stimulating hair cells
  - -> sound waves travel through helicotrema -> down the scala tympani -> to the round window
- Low frequency waves act at apex of cochlea
- High frequency waves act at base of cochlea
Toxic lesions of the inner ear
- Etiology
  - Endogenous
    - Metabolic diseases
      - Diabetes mellitus
      - Uraemia
    - Bacterial toxins
  - Exogenous
    - Aminoglycosides
    - Loop diuretics
    - Cytostatic drugs
    - Salicylates
    - Industrial solvents
    - Heavy metals
    - Alcohol
    - Illegal drugs
- Serous labyrinthitis
  - Bacterial toxins from chronic otitis media‎