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The utricle and saccule are part of the balancing system (membranous labyrinth) in the vestibule of the bony labyrinth (small oval chamber). [1] They use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation. The utricle detects linear accelerations and head-tilts in the horizontal plane.
The vestibular nerve is one of the two branches of the vestibulocochlear nerve (the cochlear nerve being the other). In humans the vestibular nerve transmits sensory information from vestibular hair cells located in the two otolith organs (the utricle and the saccule) and the three semicircular canals via the vestibular ganglion of Scarpa.
Humans have two otolithic organs on each side, one called the utricle, the other called the saccule. The utricle contains a patch of hair cells and supporting cells called a macula. Similarly, the saccule contains a patch of hair cells and a macula. Each hair cell of a macula has forty to seventy stereocilia and one true cilium called a ...
The ganglion contains the cell bodies of bipolar neurons whose peripheral processes form synaptic contact with hair cells of the vestibular sensory end organs. [2] These include hair cells of the cristae ampullaris of the semicircular duct, and the maculae of the utricle and saccule. [1] [3]
The utricular macula lie horizontal in the utricle, while the saccular macula lies vertical in the saccule. Every hair cell in these sensory beds consist of 40-70 stereocilia and a kinocilium. [2] The stereocilia and kinocilium are embedded in the otolithic membrane and are essential in the function of the otolith organs. The hair cells are ...
Various clusters of hair cells within the inner ear may instead be responsible; for example, bony fish contain a sensory cluster called the macula neglecta in the utricle that may have this function. Although fish have neither an outer nor a middle ear, sound may still be transmitted to the inner ear through the bones of the skull, or by the ...
In mammalian outer hair cells, the varying receptor potential is converted to active vibrations of the cell body. This mechanical response to electrical signals is termed somatic electromotility; [13] it drives variations in the cell's length, synchronized to the incoming sound signal, and provides mechanical amplification by feedback to the traveling wave.
Hair cells send signals down sensory nerve fibers which are interpreted by the brain as motion. In addition to sensing acceleration of the head, the otoliths can help to sense the orientation via gravity's effect on them. When the head is in a normal upright position, the otolith presses on the sensory hair cell receptors. This pushes the hair ...