Among all sense organs, the most complex transformations occurring during reception of a stimulus are those observed in the organ of hearing, found only in the most highly organized animals, namely vertebrates and insects. Sound reception must be considered as mechanoreception that has attained the highest stage of development. With the aid of such a system of mechanoreceptors an animal can determine the character of the substrate with which it comes into contact, the velocity of a stream of water or air, the depth of immersion, the pressure of a liquid in its own vessels and cavities, the movement and position of its own muscles and joints (proprioception), changes in the Earth’s gravitational field and angular accelerations, vibrations, and finally, sounds of specific frequency and intensity. In vertebrates, mechanoreception takes place with the aid of special encapsulated and nonencapsulated corpuscules, as well as by means of specialized secondary sensory cells that have no central process of their own and transmit information directly to synapses, but are equipped with a cluster of stereocilia polarly opposed by a single kinocilium containing 9 × 2+2 fibrils. In insects, mechanoreception is achieved by means of sensilla. The peripheral process of receptor cells in sensilla is a modified flagellum containing 9 × 2+0 fibrils, which is attached to the cuticular elements of sensilla.
KeywordsHair Cell Tympanic Membrane Nerve Ending Basal Body Outer Hair Cell
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