A cell that is equipped with hairlike cilia and specialized for detecting movement of the surrounding medium, whether water or air; hence, it transduces mechanical stimuli into electrical stimuli, in the form of nerve impulses in associated sensory nerves. Hair cells occur in various types of vertebrate sensory organs, including the mammalian ear and the lateral-line system of fishes and amphibians. A characteristic feature is the array of cilia projecting from the cell’s apical surface. These typically include a single long kinocilium and 20–300 much shorter stereocilia. The shafts of the cilia are usually embedded in an accessory structure, such as the cupula in the ampulla of the inner ear. Movement of the accessory structure causes the cilia to bend, which changes the cell’s membrane potential and alters the pattern of impulses in the afferent sensory neuron.