Module 1 of 12

Introduction & Overview

What the vestibular system does, and why its physiology underpins the diagnosis of vertigo.

The vestibular system is an evolutionarily preserved apparatus for balance, posture, spatial orientation, and the coordination of eye movement. Understanding its physiology is the foundation for diagnosing and managing vertigo.

Deep in each inner ear sits a set of tiny sensors that detect how the head moves and where it is in space. They feed the brainstem and cerebellum, which respond by steadying the eyes and adjusting posture so the world stays stable as you move.

The vestibular apparatus combines peripheral and central inputs to perceive head motion and to align gaze, most visibly through the vestibulo-ocular reflex. The peripheral sensors are the three semicircular canals, which respond to angular acceleration, and the two otolith organs — utricle and saccule — which detect linear acceleration and head tilt. Their signals reach the brainstem and cerebellum, which generate reflexive responses to stabilize gaze and maintain equilibrium 28.

A working grasp of vestibular physiology underpins the diagnosis of benign paroxysmal positional vertigo, vestibular neuritis, bilateral vestibulopathy, and central vestibular syndromes. The same physiology explains the diagnostic tests — the video head impulse test, caloric irrigation, and vestibular evoked myogenic potentials — each of which probes a specific limb of the system13.

externalTMmiddleinner — labyrinth + cochleavestibular apparatus
The vestibular apparatus sits within the inner ear, alongside the cochlea. Sound is conducted through the external canal, tympanic membrane, and ossicles, while the labyrinth is bathed in inner-ear fluids that transduce head motion independently of hearing.
UtricleSacculeAnterior canalPosterior canalHorizontal canalampullaeCochleaVIII nerve
The membranous labyrinth: three semicircular canals arranged near-orthogonally, the vestibule housing the utricle and saccule, and the cochlea. Endolymph fills the entire space; ampullae mark the canal bases where the sensory cristae sit.

How this atlas is organised

Modules move from evolution and embryology through fluid homeostasis, hair-cell transduction, the canal and otolith sensors, afferent coding, the vestibulo-ocular and vestibulospinal reflexes, cerebellar modulation, and visual–vestibular integration, closing with clinical correlates. Every module is layered for Foundation, Trainee, and Clinician readers.