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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.
Resembling hair-like projections, the stereocilia are arranged in bundles of 30–300. [3] Within the bundles the stereocilia are often lined up in several rows of increasing height, similar to a staircase. At the core of these hair-like stereocilia are rigid cross-linked actin filaments, which can renew every
The inner ear in these species consists of a single vestibular chamber, although in lampreys, this is associated with a series of sacs lined by cilia. Lampreys have only two semicircular canals, with the horizontal canal being absent, while hagfish have only a single, vertical, canal. [12]
Some motile cilia lack the central pair, and some non-motile cilia have the central pair, hence the four types. [5] [7] Most non-motile cilia, termed primary cilia or sensory cilia, serve solely as sensory organelles. [8] [9] Most vertebrate cell types possess a single non-motile primary cilium, which functions as a cellular antenna.
The stereocilia number from fifty to a hundred in each cell while being tightly packed together [2] and decrease in size the further away they are located from the kinocilium. [ 3 ] Mammalian cochlear hair cells are of two anatomically and functionally distinct types, known as outer, and inner hair cells.
One kinocilium is the longest cilium located on the hair cell next to 40–70 stereocilia. During movement of the body, the hair cell is depolarized when the stereocilia move toward the kinocilium. The depolarization of the hair cell causes neurotransmitter to be released and an increase in firing frequency of cranial nerve VIII. When the ...
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 deflected by structures called otoconia.
There are roughly twelve thousand OHCs in each human ear, and these are arranged in up to five rows. Each OHC has small tufts of 'hairs', or cilia, on their upper surface known as stereocilia, and these are also arranged into rows which are graded in height. There are approximately 140 stereocilia on each OHC. [13]