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In essence, the very fact that the ear may have evolved multiple times see Fritzsch, provides a rich body of comparative data upon which to evaluate evolution of the ear. Unique and important information about the basic mechanisms of hearing come from research on diverse species.
Often specific questions regarding human auditory function can be approached and answered by selecting a species for study that allow exploration of the auditory system in ways that are not easy to accomplish in humans. Clearly, the science of hearing and auditory neuroscience has benefited greatly from the comparative approach and from viewing animals in the context of their evolutionary relationships.
Our faculty share a common research interest in hearing as well as a common interest in the insights derived from comparative hearing and the evolution of hearing. Our research questions range from the cellular and molecular structure of the ear to aging in the auditory system. Our labs use experimental approaches that range from molecular biology to psychoacoustics to imaging. Organisms studied include insects, fish, amphibians, reptiles, birds, non-human mammals, and humans.
The breadth of experimental approaches and subjects, combined with a common interest among investigators in comparative evolutionary issues, provides opportunities for research training at the graduate and postdoctoral levels that, we believe, exists nowhere else. We combine our research training with outstanding professional training in the hearing sciences. The major goal of our program is to produce auditory neuroscientists who understand the diversity of hearing mechanisms and the evolution of the auditory system so that they are able to identify appropriate models to ask questions of fundamental importance central to the function of the auditory system in health and in disease.
Examples include understanding of hair cell repair and regeneration using fish and birds; e. Our theme of the comparative and evolutionary biology of hearing follows naturally from the work of our Core Faculty.
Yun Doo Chung and Jeongmi Lee
Our location in the greater Washington DC area provides unique training opportunities for our students through collaborations with investigators in other programs and groups. This partnership fosters close collaborative research training opportunities for doctoral and postdoctoral students that involve strong interactions between co-mentors at both institutions. The collaboration also provides significant additional opportunities for training of doctoral and postdoctoral students in areas of greatest strength at NIDCD, including molecular biology, cellular biology, and communication disorders.
The NIDCD faculty open their labs for specialized training and research opportunities for trainees who are doing their primary work at UMD, and may also serve as co-mentors for these students. The inferior division of the labyrinth always contains a saccule with its macula, the macula sacculi, but the derivatives of the saccule vary greatly in the different vertebrate classes.
In teleosts bony fishes , amphibians, reptiles, and birds there is a lagena a curved, flask-shaped structure , with its macula, the macula lagenae. Only the amphibians have a papilla amphibiorum , which is located near the junction of the utricle and the saccule. In some amphibians and in all reptiles, birds, and mammals, there is a papilla basilaris, which is usually called a cochlea in the higher forms, in which it is highly detailed. The elaborate sensory structure of higher types of ears, containing hair cells and supporting elements, is called the organ of Corti.
The macular endings consist of plates of ciliated cells cells with short, hairlike projections along with accessory cells, all surmounted by an otolith a calcareous mass containing numerous particles of calcium carbonate embedded in a gelatinous matrix or, in teleosts, by one large mass of calcium carbonate. The crista endings contain moundlike groups of sensory cells with supporting cells; the sensory cells have elongated cilia that are embedded in a gelatinous body, the cupula, which forms a sort of valve across an expanded portion of each semicircular canal.
The papillae contain plates or ribbons of ciliated cells in a structural framework that lies on a movable membrane, except in amphibians, in which the papillae are on a solid base. These ciliated cells are not surmounted by an otolithic mass or a cupula, but some of the cilia are attached either directly or indirectly to a tectorial membrane a membrane with one edge fixed to a stationary base, thus anchoring the cilia or to an inertia body a mass lying over the ciliated cells and restraining the movements of the cilia.
The endings have different functions: the macular organs serve primarily as gravity receptors and detectors of sudden movements; the crista organs serve for the perception of rotational acceleration; and the papillae serve for hearing.
As structural relations suggest, the auditory endings are derived either from the other labyrinthine receptors or from the primitive labyrinthine epithelium. The cyclostomes and the elasmobranchs e.
There are, nevertheless, two possible ways by which some of these cartilaginous fishes, especially the sharks , react to sounds in the water: by means of the macular organs and by means of the lateral-line apparatus. It is in the bony fishes teleosts that a true ear whose function is hearing first appears among the vertebrates.
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This ear, which occurs in a number of forms, has varying degrees of effectiveness as a sound receiver; some fishes hear well, others poorly. The differences arise, at least in part, from the accessory mechanisms that aid in the utilization of sound energy. In most fishes, especially in many marine forms, the auditory mechanism is relatively simple, consisting of macular endings that evidently have been diverted from their primitive functions as detectors of gravity and motion. The important change is not in the structure of the end organ but in its innervation—the nerve supply has connections that transmit auditory information.
It is thought that in most teleosts the change to an auditory function has occurred in the saccular macula, and probably the lagenar macula as well, and that the utricular macula continues as a receptor for gravity and motion.
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The simple macular ending of the teleost ear is stimulated by sound through the operation of an inertia principle. Sound waves pass readily through the water and into the body of the fish, causing most of the tissues to vibrate in a uniform manner.http://co.organiccrap.com/154640.php
Evolution Of The Vertebrate Auditory System
The macular otolith, however, represents a discontinuity; because its density is greater than that of the other tissues, it exhibits an inertia effect resistance to movement. Its motions not only lag behind those of the surrounding tissues but are probably of lesser amplitude as well. Accordingly, a sound creates a relative motion between the otoliths and the other tissues.