Representation of the inner ear and zoom at the level of the macula (organ of the static equilibrium). Located at the level of the inner ear, the vestibular system is the organ of equilibrium ; it is constituted of semi-circular canals and a macula (in red), thickening of the utricle and saccule inner walls (in transparency, in pinkish). The macula is composed of hair cells (in orange), constituting the sensorial receptors, and of supporting cells (in pink). Each hair cell is possessed of 40 to 70 stereocilia (microvillosities) and of a single kinocilium, longer true cilium. The supporting cells secrete a gelatinous substance forming the otolithic membrane, in which embed the stereocilia and kinocilia. This membrane is covered with a layer of aragonite cristals (calcium carbonate), the otoliths (in grey). Each hair cell forms a synapse with a sensitive neuron (in yellow) and a motor neuron (in green) of the vestibular nerve, branch of the auditory nerve. See the image 0229406 for the macula alone, the image 0228806 for the inner ear alone, the images 5606406 and 5606506 for the functionning of the macula.
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