EAR, HUMAN


Meaning of EAR, HUMAN in English

organ of hearing and equilibrium that detects and analyzes noises by transduction (or the conversion of sound waves into electrochemical impulses) and maintains the sense of balance (equilibrium). Figure 1: Structure of the human ear. The human ear, like that of other mammals, contains sense organs that serve two quite different functions: that of hearing and that of postural equilibrium and coordination of head and eye movements. Anatomically the ear has three distinguishable parts: the outer, middle, and inner ear (Figure 1). The outer ear consists of the visible portion called the auricle, or pinna, which projects from the side of the head, and the short external auditory canal, the inner end of which is closed by the tympanic membrane, commonly called the eardrum. The function of the outer ear is to collect sound waves and guide them to the tympanic membrane. The middle ear is a narrow, air-filled cavity in the temporal bone. It is spanned by a chain of three tiny bonesthe malleus (hammer), incus (anvil), and stapes (stirrup), collectively called the auditory ossicles. This ossicular chain conducts sound from the tympanic membrane to the inner ear, which has been known since the time of Galen (2nd century AD) as the labyrinth. It is a complicated system of fluid-filled passages and cavities located deep within the rock-hard petrous portion of the temporal bone. The inner ear consists of two functional units: the vestibular apparatus, consisting of the vestibule and semicircular canals, which contains the sensory organs of postural equilibrium; and the snail-shell-like cochlea, which contains the sensory organ of hearing. These sensory organs are highly specialized endings of the eighth cranial nerve, also called the vestibulocochlear nerve. Additional reading Anthony F. Jahn and Joseph Santos-Sacchi (eds.), Physiology of the Ear (1988), collects essays treating many different aspects of the subject; especially useful is the succinct historical account of studies of the ear and hearing by Joseph E. Hawkins, Jr., Auditory Physiological History: A Surface View, pp. 128. A reliable and readable introductory treatise is S.S. Stevens et al., Sound and Hearing, rev. ed. (1980). Although somewhat more technical, Hallowell Davis and S. Richard Silverman, Hearing and Deafness, 4th ed. (1978), was also written for the nonspecialist. Georg Von Bksy, The Ear, Scientific American, 197(2):6678 (August 1957), by a foremost research authority on the ear, describes in lay terms the mechanism of hearing, while his Experiments in Hearing, trans. and ed. by E.G. Wever (1960, reprinted 1977), is the best source of information about the experimental work that won him the Nobel Prize, although it is not recommended for the novice. A well-illustrated chapter on the anatomy of the ear may be found in Don W. Fawcett, A Textbook of Histology, 12th ed. (1994). For comparative anatomy from fishes to humans, the drawings in Gustaf Retzius, Das Gehrorgan der Wirbelthiere, 2 vol. (188184), are still unequaled, although the work is not widely available. Other classics in the field of hearing include S.S. Stevens and Hallowell Davis, Hearing: Its Psychology and Physiology (1938, reprinted 1983); E.G. Wever, Theory of Hearing (1949, reissued 1970), including a good historical treatment of theories of hearing as developed through the centuries; and E.G. Wever and Merle Lawrence, Physiological Acoustics (1954), concerned mainly with middle-ear mechanics. A.J. Hudspeth, How the Ear's Works Work, Nature, 341(6241):397404 (Oct. 5, 1989), gives an account of the role of hair cells in hearing. Further details are found in Lewis G. Tilney and Mary S. Tilney, Actin Filaments, Stereocilia, and Hair Cells: How Cells Count and Measure, Annual Review of Cell Biology, 8:257274 (1992). As an accessible introduction to the clinical concerns of otology and audiology, John Ballantyne, M.C. Martin, and Antony Martin (eds.), Deafness, 5th ed. (1993), remains unsurpassed. For detailed, up-to-date treatments of other topics and problems considered in this section, the series Springer Handbook of Auditory Research is highly recommended, especially vol. 1, The Mammalian Auditory Pathway: Neuroanatomy, ed. by Douglas B. Webster, Arthur N. Popper, and Richard R. Fay (1992), vol. 2, The Mammalian Auditory Pathway: Neurophysiology, ed. by Arthur N. Popper and Richard R. Fay (1992), vol. 7, Clinical Aspects of Hearing, ed. by Thomas R. Van de Water, Arthur N. Popper, and Richard R. Fay (1996), and vol. 8, The Cochlea, ed. by Peter Dallos, Arthur N. Popper, and Richard R. Fay (1996). Information on the anatomy and physiology of the vestibular system and the disorders, peripheral and central, that can affect it may be found in the still-useful work by Ralph F. Naunton (ed.), The Vestibular System (1975). Joseph E. Hawkins

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