Utricle
Utriculus
Also known as: utriculus, macula of utricle
The larger otolith organ of the membranous labyrinth, lying in the elliptical recess of the vestibule; its roughly horizontal macula senses head tilt and horizontal linear acceleration.
Overview
The utricle is an oblong membranous sac in the posterosuperior part of the vestibule. The three semicircular ducts open into it by five openings, and it connects to the saccule and endolymphatic duct by the utriculosaccular duct.
Its macula (≈2 × 3 mm) lies on the floor and anterior wall, approximately in the horizontal plane when the head is upright (tilted up ≈30° anteriorly). It is covered by an otolithic membrane with otoconia. When the head tilts or accelerates horizontally (forward–backward, side to side), the otoconial mass lags or slides under gravity, deflecting stereocilia; hair cells on either side of the striola have opposite polarities, so the pattern of excitation across the macula encodes the direction. The utricle cannot distinguish tilt from linear acceleration on its own (Einstein's equivalence principle); the brain resolves this using canal and visual input.
Otoconia dislodged from the utricular macula (by ageing, head injury or inner-ear disease) can enter a semicircular canal — the cause of benign paroxysmal positional vertigo.
- Location
Elliptical recess of the vestibule, posterosuperior to the saccule.
Anatomy
- Innervation
Utricular nerve → superior vestibular nerve (vestibular ganglion).
- Histology
Macula: columnar supporting cells and type I/II hair cells with kinocilia; gelatinous otolithic membrane carrying otoconia (calcium carbonate with otoconin-90).
Function
- Sense head tilt relative to gravity in the horizontal plane
- Sense horizontal linear acceleration (e.g. car accelerating)
- Drive otolith–ocular (ocular counter-roll) and vestibulospinal postural reflexes
Clinical significance
Source of BPPV otoconia
Degenerating utricular otoconia migrate into the dependent posterior canal; BPPV is commoner with age, after head injury and with osteoporosis/vitamin D deficiency.
Ocular tilt reaction
Damage to utricular pathways (peripheral or brainstem) causes head tilt, skew deviation and ocular torsion; skew deviation in acute vertigo suggests a central (stroke) cause.
Compiled from standard anatomy and physiology references — see the Special Senses sources. For education only; not medical advice.