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stereocilium (pl. stereocilia) A relatively short, nonmotile cilium, some 20 to 300 of which form an array on the apical surface of a sensory hair cell. The stereocilia are usually associated with a single, much longer kinocilium but lack the 9 + 2 arrangement of internal microtubules characteristic of undulipodia. Instead, their shaft contains numerous fine longitudinal actin filaments. Bending of the kinocilium causes the array of stereocilia to bend en masse, thereby changing the pattern of impulses in the adjacent sensory neuron.