. Principles of modern biology. Biology. Responses of Higher Animals: The Receptors - 425 COCHLEA or„,o,n,„,r> SCALA MEMBRANOUS SCALA SEMJ?R.^R VESTIBULk CANAL .TYMPANI CANALS. EUSTACHIAN TUBE VESTIBULE Fig. 23-8. Structure of the human ear. The shaded portions with heavy outlines represent bone; the lighter lines represent membranous structures. with fluid and lined with hair cells. The sac- cule and utricle appear to function more or less like statocysts, but the semicircular canals are concerned with the perception of rota- tional movement, not of position. The differ- ent semicircular c
. Principles of modern biology. Biology. Responses of Higher Animals: The Receptors - 425 COCHLEA or„,o,n,„,r> SCALA MEMBRANOUS SCALA SEMJ?R.^R VESTIBULk CANAL .TYMPANI CANALS. EUSTACHIAN TUBE VESTIBULE Fig. 23-8. Structure of the human ear. The shaded portions with heavy outlines represent bone; the lighter lines represent membranous structures. with fluid and lined with hair cells. The sac- cule and utricle appear to function more or less like statocysts, but the semicircular canals are concerned with the perception of rota- tional movement, not of position. The differ- ent semicircular canals lie in different planes, each at right angles to the others, and when the body starts to move in a given direction, inertia displaces the fluid in some one of the canals, exciting some local group of the hair- bearing receptor cells. If the movement stops, the momentum of the fluid displaces the fluid in an opposite direction, which excites some other group of hair cells. In fish and other lower Vertebrata, the labyrinth is mainly an organ of equilibrium; but in land vertebrates part of the labyrinth develops into the cochlea, the essential organ of hearing (Fig. 23-8). The cochlea contains a large number of hair-bearing sensory cells (Fig. 23-9), which are stimulated by sound vibrations, transmitted from the external air, through the tympanic cavity, to the fluid in the cochlea. Perception of the pitch and quality of sounds depends on the fact that the different hair cells of the cochlea are stimulated by vibrations of different fre- quencies. Probably insects are the only other animals that possess specialized organs of hearing, but the ears of insects vary widely as to structure and position in the different species. Proprioceptors. The perception of move- ment and position of the body as a whole is localized in the labyrinth, but each sepa- rate muscle and tendon is equipped with re- ceptors, called proprioceptors, which play an essential role in coordinating the
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