Biophysics of directional hearing in the American alligator (Alligator mississippiensis). 2014

Hilary S Bierman, and Jennifer L Thornton, and Heath G Jones, and Kanthaiah Koka, and Bruce A Young, and Christian Brandt, and Jakob Christensen-Dalsgaard, and Catherine E Carr, and Daniel J Tollin
Center for Comparative and Evolutionary Biology of Hearing, Department of Biology, University of Maryland College Park, College Park, MD 20742, USA.

Physiological and anatomical studies have suggested that alligators have unique adaptations for spatial hearing. Sound localization cues are primarily generated by the filtering of sound waves by the head. Different vertebrate lineages have evolved external and/or internal anatomical adaptations to enhance these cues, such as pinnae and interaural canals. It has been hypothesized that in alligators, directionality may be enhanced via the acoustic coupling of middle ear cavities, resulting in a pressure difference receiver (PDR) mechanism. The experiments reported here support a role for a PDR mechanism in alligator sound localization by demonstrating that (1) acoustic space cues generated by the external morphology of the animal are not sufficient to generate location cues that match physiological sensitivity, (2) continuous pathways between the middle ears are present to provide an anatomical basis for coupling, (3) the auditory brainstem response shows some directionality, and (4) eardrum movement is directionally sensitive. Together, these data support the role of a PDR mechanism in crocodilians and further suggest this mechanism is a shared archosaur trait, most likely found also in the extinct dinosaurs.

UI MeSH Term Description Entries
D003056 Cochlear Nerve The cochlear part of the 8th cranial nerve (VESTIBULOCOCHLEAR NERVE). The cochlear nerve fibers originate from neurons of the SPIRAL GANGLION and project peripherally to cochlear hair cells and centrally to the cochlear nuclei (COCHLEAR NUCLEUS) of the BRAIN STEM. They mediate the sense of hearing. Acoustic Nerve,Auditory Nerve,Acoustic Nerves,Auditory Nerves,Cochlear Nerves,Nerve, Acoustic,Nerve, Auditory,Nerve, Cochlear,Nerves, Acoustic,Nerves, Auditory,Nerves, Cochlear
D004432 Ear, Middle The space and structures directly internal to the TYMPANIC MEMBRANE and external to the inner ear (LABYRINTH). Its major components include the AUDITORY OSSICLES and the EUSTACHIAN TUBE that connects the cavity of middle ear (tympanic cavity) to the upper part of the throat. Tympanic Cavity,Tympanum,Middle Ear,Cavities, Tympanic,Cavity, Tympanic,Ears, Middle,Middle Ears,Tympanic Cavities,Tympanums
D006257 Head The upper part of the human body, or the front or upper part of the body of an animal, typically separated from the rest of the body by a neck, and containing the brain, mouth, and sense organs. Heads
D000489 Alligators and Crocodiles Large, long-tailed reptiles, including caimans, of the order Loricata. Caimans,Crocodiles,Alligators,Caymans,Alligator,Caiman,Cayman,Crocodile,Crocodiles and Alligators
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D013016 Sound A type of non-ionizing radiation in which energy is transmitted through solid, liquid, or gas as compression waves. Sound (acoustic or sonic) radiation with frequencies above the audible range is classified as ultrasonic. Sound radiation below the audible range is classified as infrasonic. Acoustic Waves,Elastic Waves,Sonic Radiation,Sound Waves,Acoustic Wave,Elastic Wave,Radiation, Sonic,Radiations, Sonic,Sonic Radiations,Sound Wave,Sounds,Wave, Acoustic,Wave, Elastic,Wave, Sound,Waves, Acoustic,Waves, Elastic,Waves, Sound
D013017 Sound Localization Ability to determine the specific location of a sound source. Auditory Localization,Auditory Localizations,Localization, Auditory,Localization, Sound,Localizations, Auditory,Localizations, Sound,Sound Localizations
D014432 Tympanic Membrane An oval semitransparent membrane separating the external EAR CANAL from the tympanic cavity (EAR, MIDDLE). It contains three layers: the skin of the external ear canal; the core of radially and circularly arranged collagen fibers; and the MUCOSA of the middle ear. Eardrum,Eardrums,Membrane, Tympanic,Membranes, Tympanic,Tympanic Membranes
D016057 Evoked Potentials, Auditory, Brain Stem Electrical waves in the CEREBRAL CORTEX generated by BRAIN STEM structures in response to auditory click stimuli. These are found to be abnormal in many patients with CEREBELLOPONTINE ANGLE lesions, MULTIPLE SCLEROSIS, or other DEMYELINATING DISEASES. Acoustic Evoked Brain Stem Potentials,Auditory Brain Stem Evoked Responses,Brain Stem Auditory Evoked Potentials,Evoked Responses, Auditory, Brain Stem,Acoustic Evoked Brain Stem Potential,Acoustic Evoked Brainstem Potential,Acoustic Evoked Brainstem Potentials,Auditory Brain Stem Evoked Response,Auditory Brain Stem Response,Auditory Brain Stem Responses,Auditory Brainstem Evoked Response,Auditory Brainstem Evoked Responses,Auditory Brainstem Responses,Brain Stem Auditory Evoked Potential,Brainstem Auditory Evoked Potential,Brainstem Auditory Evoked Potentials,Evoked Potential, Auditory, Brainstem,Evoked Potentials, Auditory, Brainstem,Evoked Response, Auditory, Brain Stem,Evoked Response, Auditory, Brainstem,Evoked Responses, Auditory, Brainstem,Auditory Brainstem Response,Brainstem Response, Auditory,Brainstem Responses, Auditory,Response, Auditory Brainstem,Responses, Auditory Brainstem
D055592 Biophysical Phenomena The physical characteristics and processes of biological systems. Biophysical Concepts,Biophysical Processes,Biophysical Phenomenon,Biophysical Process,Biophysical Concept,Concept, Biophysical,Concepts, Biophysical,Phenomena, Biophysical,Phenomenon, Biophysical,Process, Biophysical,Processes, Biophysical

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