🦻 Distribution of Endolymph and Perilymph in the Inner Ear
The inner ear is a highly specialized sensory organ responsible for both hearing and balance. It contains two distinct fluids — endolymph and perilymph — each occupying specific compartments and playing unique roles in maintaining auditory and vestibular function. Their ionic compositions and locations are key to how sound and movement are detected.
💧 Endolymph: The Potassium-Rich Fluid
Endolymph is unique because it has high potassium (K⁺) and low sodium (Na⁺) concentrations. This unusual ionic environment is essential for activating sensory hair cells in the inner ear.
Found in:
Semicircular ducts (balance)
Utricle and saccule (detect position and motion)
Scala media (important for hearing)
🌊 Perilymph: The Sodium-Rich Fluid
Perilymph is similar to cerebrospinal fluid, containing high sodium (Na⁺) and low potassium (K⁺). It surrounds sensitive structures of the inner ear, cushioning them and aiding in sound wave transmission.
Found in:
Semicircular canals
Scala vestibuli
Scala tympani
📊 Comparison Table
| Feature | Endolymph | Perilymph |
|---|---|---|
| Ionic Composition | High K⁺, Low Na⁺ | High Na⁺, Low K⁺ |
| Location | Semicircular ducts, Utricle, Saccule, Scala Media | Semicircular canals, Scala Vestibuli, Scala Tympani |
| Main Function | Generates electrical signals for sensory transduction | Protects structures, transmits sound waves |
🎯 Role in Hearing and Balance
Hearing: Sound vibrations cause the stapes to push against the oval window, moving perilymph in the scala vestibuli. This motion displaces endolymph in the scala media, stimulating hair cells that send electrical signals to the brain.
Balance: Movement of the head shifts the endolymph in the semicircular ducts. This bends the hair cells in the ampullae, helping the brain detect motion and orientation.
💡 Did you know?
Disorders like Ménière’s disease are linked to abnormal amounts of endolymph, causing vertigo, tinnitus, and fluctuating hearing loss.
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