utriclen

The utricle is one of the two otolith organs in the vestibular labyrinth of the inner ear. It is a small, sac-like structure located in the vestibule, a central cavity of the bony labyrinth, between the cochlea and the semicircular canals. Along with the saccule, it is responsible for detecting linear acceleration and the force of gravity.

The sensory epithelium of the utricle is called the macula utriculi. This macula contains sensory hair cells, which are mechanoreceptors. These hair cells have stereocilia and a kinocilium, and their movement stimulates nerve fibers of the vestibular nerve. The stereocilia are embedded in a gelatinous membrane called the otolithic membrane.

The otolithic membrane is covered with small calcium carbonate crystals known as otoliths or statoconia. When the head accelerates linearly or tilts in relation to gravity, the inertia of the otoliths causes them to lag behind or shift, dragging the otolithic membrane with them. This movement bends the stereocilia of the hair cells.

The bending of the stereocilia towards the kinocilium depolarizes the hair cell, increasing the release of neurotransmitters and exciting the vestibular nerve. Conversely, bending away from the kinocilium hyperpolarizes the hair cell, reducing neural activity. This information about head position and movement is transmitted to the brainstem and cerebellum, contributing to balance, spatial orientation, and coordination of eye movements.