Stereocilia ( Latin stereocilia ) are called long processes on the surface of epithelial cells . The name can be misleading as these processes are not functionally real cilia . That is why stereocilia are now also referred to as stereovilli . In contrast to cilia, stereocilia or stereovilli are not formed from microtubules , but from actin filaments . In addition, they do not have a basal body .
Stereovilli (stereocilia) are the moving parts of the mechanoreceptors of the vertebrates , so special sensory cells , the hair cells are called. In evolutionary terms, they first appeared in the lateral line organ , where they react to currents and pressure waves from the water; Then they also appeared in the organ of equilibrium and register their own changes in position and movement, and ultimately they appeared in the inner ear , where they respond to sound .
The tufts of stereovilli (bundles of hair) in the inner ear of terrestrial vertebrates have the function of motors ( motility ) in addition to their function as mechanoreceptors . They thus amplify the sound waves that stimulate them. This identity of the sensor and motor function of the stereocilia serves to improve the frequency coordination and thus the frequency resolution of the hearing organ .
They also occur in the epididymal duct ( ductus epididymidis ) and in the spermatic duct ( ductus deferens ). Here, however, they are not assigned a function in mechanoreception, but in the uptake ( absorption ) and release ( secretion ) of substances.
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