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Stereocilia (or stereovilli or villi) are non-motile apical cell modifications. They are distinct from cilia and microvilli , but are closely related to microvilli. They form single "finger-like" projections that may be branched, with normal cell membrane characteristics.
Stereocilia of frog inner ear. In the inner ear, stereocilia are the mechanosensing organelles of hair cells, which respond to fluid motion in numerous types of animals for various functions, including hearing and balance.
The hair cells have a hair bundle at the apical surface of the cell. The hair bundle consists of an array of actin-based stereocilia. Each stereocilium inserts as a rootlet into a dense filamentous actin mesh known as the cuticular plate. Disruption of these bundles results in hearing impairments and balance defects.
The macula of saccule lies in a nearly vertical position. It is a 2mm by 3mm patch of hair cells. Each hair cell of the macula contains 40 to 70 stereocilia and one true cilia, called a kinocilium. A gelatinous cover called the otolithic membrane envelops the tips of the stereocilia and kinocilium.
The kinocilium is the only sensory aspect of the hair cell and is what causes hair cell polarization. The tips of these stereocilia and kinocilium are embedded in a gelatinous layer, which together with the statoconia form the otolithic membrane. [2] This membrane is weighted with calcium carbonate-protein granules called otoliths.
The first of these layers is the otolithic membrane which uniformly distributes the force of inertia of the non-uniform otoconia mass to all stereocilia bundles. The second layer formed by columnar filaments secures the membrane above the surface of the epithelium. [5]
Pseudostratified columnar epithelia with stereocilia are located in the epididymis. Stereocilia of the epididymis are not cilia because their cytoskeleton is composed of actin filaments, not microtubules. [3] They are structurally and molecularly more similar to microvilli than to true cilia. [dubious – discuss]
The stereocilia atop the IHCs move with this fluid displacement and in response their cation, or positive ion selective, channels are pulled open by cadherin structures called tip links that connect adjacent stereocilia. [9] The organ of Corti, surrounded in potassium-rich fluid endolymph, lies on the basilar membrane at the base of the scala ...