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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 hair cells are the primary auditory receptor cells and they are also known as auditory sensory cells, acoustic hair cells, auditory cells or cells of Corti. The organ of Corti is lined with a single row of inner hair cells and three rows of outer hair cells. The hair cells have a hair bundle at the apical surface of the cell.
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.
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]
Overlying the hair cells and their hair bundles is a gelatinous layer and above that layer is the otolithic membrane. [1] The utricle serves to measure horizontal accelerations and the saccule responds to vertical accelerations. The reason for this difference is the orientation of the macula in the two organs. The utricular macula lie ...
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 ...
Cross-section through the spiral organ of Corti at greater magnification, showing position of the hair cells on the basement membrane. The organ of Corti is located in the scala media of the cochlea of the inner ear between the vestibular duct and the tympanic duct and is composed of mechanosensory cells, known as hair cells. [2]