Dive into the mystery of the vestibule, the gyroscope of the inner ear! Discover how it detects movements and orientations, a masterpiece of biology.
Published on October 30, 2025
The vestibule, nestled in the inner ear, functions as a biological gyroscope. It converts head accelerations into electrical signals through the semicircular canals (rotations) and otoliths (translations and gravity).
The semicircular canals contain endolymph and a gelatinous cupula. During rotation, the fluid remains stationary for a few milliseconds → deformation of the cupula → tilting of the cilia → variation in nerve frequency. One canal excites, while the other inhibits, encoding direction and speed.
The otoliths (utriculus, saccule) have a gelatinous membrane weighted with crystals. In cases of linear acceleration or tilting, the otoconia move and shear the cilia. This allows encoding of magnitude and angle relative to vertical.
The afferents reach the vestibular nuclei → ocular motoneurons (VOR), extensor motoneurons (vestibulo-spinal), cerebellum, and cortex (perception). Normal VOR gain ≈ 1; if < 0.7 → oscillopsies, instability.
The canals measure rotations, while the otoliths measure translations/inclinations. Together, they feed stabilizing reflexes and inform the brain of spatial orientation.
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