The two sensors of linear acceleration and head tilt — the maculae, the otoconia-weighted otolithic membrane, the striola, and how gravity and translation are transduced.
Two sacs in the vestibule
The otolith organs are two membrane-lined sacs — the utricle and the saccule — sitting in the vestibule of the inner ear, between the semicircular canals and the cochlea. Together they are the organs of linear motion and head tilt.8
The macula and the otolithic membrane
Each organ contains a sensory patch called a macula — a sheet of hair cells. Their hairs project up into the otolithic membrane, a gel layer studded with tiny calcium-carbonate crystals called otoconia.8
Otoconia
Microscopic calcium-carbonate crystals embedded in the otolithic membrane. Their weight gives the membrane inertia, so it lags during acceleration and shifts under gravity — the physical basis of otolith sensing.
Sensing tilt and translation
When the head tilts or accelerates in a straight line, the heavy otolithic membrane lags behind or slides under gravity. That shear bends the hair-cell bundles, changing how fast the cells fire — exactly as in the semicircular canals.4
Clinical relevance and VEMP testing
Otolith dysfunction tends to cause imbalance, a sense of tilt, and difficulty judging orientation, rather than the spinning vertigo typical of canal disorders.62