In the bony vestibule, 2 recesses are present – spherical and elliptical.
Saccule of membranous labyrinth is lodged in spherical recess of bony labyrinth. Likewise, utricle is lodged in elliptical recess.
Both these saccule and utricle are called as otolith organs. They contain otoconia (stone like crystals studded on surface of macula) made up of calcium carbonate.
If these otoconia gets dislodged and enter semicircular canal (most commonly posterior), it causes vertigo. This condition is called BPPV (Benign Paroxysmal Positional Vertigo). Patients complains of vertigo on changing head position lasting for a few seconds. Dix-hallpike manoeuvre is done for diagnosis & Epley’s manoeuvre is done for treatment. BPPV is the most common cause of peripheral vertigo. (Central vertigo means vertigo due to CNS pathology).
Saccule is responsible for vertical linear movements and utricle is responsible for horizontal linear movements.
The structural and functional units sensing these linear movements are called maculae.