Overview stereocilia (Stereocilia):
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Stereocilia or stereovilli (Terminologia histologica: Stereocilia;
Stereovilli) are immotile long protrusions of the cell membrane.
|outer hair cell stereocilia
organ of Corti (guinea pig)
|stereocilium = sensory cilia of an inner
hair cell of the ear (guinea-pig)
|sensory cilia of an
outer hair cell (guinea-pig)
They contain cytoplasm in which bundles of actin
filaments are embedded. The latter are anchored basally to the
web and apically to the thickened top of the cell
There are two different kinds of stereocilia:
1.) sensory cilia of sensory epithelia
Here the long, finger-like stereocilia are seen in rows paralell to
each other. They are anchored in a cuticula which is rich in filaments.
Stereocilia of inner and outer hair cells of the organ
of Corti in the inner ear are about 5 µm in length. Sensory
cells of the macula sacculi or utriculi in the labyrith possess
cilia which are 5 - 15 µm in length. Type I (bottle-like)
and type II (cylindrical) hair cells on the cristae ampullares of
the semicircular canals show even longer stereocilia: 5 - 25 µm.
In cross sections the round diameter of stereocilia varies from
nm at the base to 250 nm slightly above. Sensory stereocilia
are similar in construction and appearance to microvilli with the following
exceptions: they are longer and greater in diameter, their basis is thinner
than the parts located above; a glycocalyx
and antennulae are not encountered. Stereocilia belong to secondary
sensory cells and change the frequency of generated action
potentials depending on direction when being sheared or bend.
2.) fused long microvilli of the
duct or the first third of the
Here stereocilia appear as 3 - 6 µm long fused protrusions
of the cytoplasm that have
no round but bizarre diameters when cross sectioned. In three dimensions
these cilia resemble bizarre coral structures.
In contrast to the sensory stereocilia this kind serves for significant
of the cell surface for better resorption of material from the seminal
fluid. The vesicles of the distinct Golgi-apparatuses
of their epithelial cells are secreted in the lumen in between the cilia.
There are no antennulae or glycocalyx
seen on top of these cilia. Actin filaments
are not as clearly visible as in microvilli
or the other kind of stereocilia.
--> further cell surface differentiations:
--> Electron microscopic atlas Overview
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Some pictures were kindly provided by Prof. H. Wartenberg;
other images, page & copyright H. Jastrow.