Physiology of the Vestibular System
The vestibular system, located within the inner ear, is responsible for maintaining balance, posture, and spatial orientation by detecting head position and movement.
Primary Components
- Semicircular Canals (3): Detect rotational (angular) acceleration of the head. Each canal contains an ampulla with a cupula, which bends hair cell stereocilia during head rotation.
- Otolith Organs (Utricle & Saccule): Detect linear acceleration and head tilt (gravity). The macula contains otoconia (calcium carbonate crystals) that shift upon movement, stimulating hair cells.
Mechanism of Action
| Feature | Detail |
|---|---|
| Transduction | Deflection of stereocilia towards the kinocilium causes depolarization; deflection away causes hyperpolarization. |
| Neural Output | Signals are transmitted via the vestibular portion of CN VIII to the vestibular nuclei in the brainstem. |
High-Yield Exam Pearl:
- Vestibulo-Ocular Reflex (VOR): A critical reflex that maintains stable gaze during head movement by producing compensatory eye movements in the opposite direction of head rotation.
- Pathology: Dysfunction in this system leads to vertigo, nystagmus, and disequilibrium. Benign Paroxysmal Positional Vertigo (BPPV) is caused by displaced otoconia entering the semicircular canals.