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(kŏk`lēə): see earear,
organ of hearing and equilibrium. The human ear consists of outer, middle, and inner parts. The outer ear is the visible portion; it includes the skin-covered flap of cartilage known as the auricle, or pinna, and the opening (auditory canal) leading to the eardrum (tympanic
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the organ of hearing within the inner ear in terrestrial vertebrates, including man; it takes the form of a protuberance of the rounded sac of the vestibule (sacculus) in the inner ear. In most terrestrial vertebrates, the cochlea contains the peripheral receptor apparatus of the auditory system.

During the course of evolution, the cochlea developed from the vestibule owing to the transition of animals to a terrestrial mode of life. The sacculus of some fishes has only one sensory patch, or macula. Most fishes, with the exception of those of the order Chimaeriformes, have a special organ of hearing in the sacculus—the lagena with a macula distinct from the original acoustic macula.

The sacculus of amphibians has two later formations outside the lagena: a basilar auditory papilla (the rudiment of the organ of Corti) and the amphibian auditory papilla, found only in amphibians. In the bullfrog the basilar papilla is a short tubule, around whose edge approximately 60 receptor hair cells form a semicircle of parallel rows. The hair cells are innervated by 350 to 500 nerve fibers. A tectorial membrane divides the lumen of the tubule. There are approximately 600 hair cells in the amphibian papilla, located in the oblong S-shaped area on the summit of the papilla and innervated by a bundle of 1,000 nerve fibers. The tectorial membrane, which is suspended from the hair cells, is attached to the opposite lower wall of the papilla. It is believed that the macula of the lagena takes part in the functioning of the vestibule and that the macula is sensitive to low-frequency vibrations and sounds. Amphibians perceive sounds by means of the basilar and amphibian papillae.

The basilar protuberance of the sacculus is more highly developed in reptiles; in crocodiles it develops into the rather long and somewhat curved canal of the cochlea. Some researchers maintain that the cochlea is independent from the lagena, and others regard the lagena as the rudiment of the cochlea. Parallel to the elongation of the basilar membrane and to the basilar membrane’s increased number of receptor auditory cells in reptiles, an increase in the size and complexity of the tectorial membrane may be observed, particularly in crocodiles. The auditory organs of birds and monotrematous animals are similar but even more complex; they retain a vestige of the lagena and its macula. In birds, the functions of the macula are associated with flight, as well as with hearing by means of bone conduction.

The later evolution of the cochlea in placental mammals led to the formation of the organ of Corti. In all mammals the cochlea has a spiral shape like that of a snail’s shell. The cochlea forms 0.25 coils in the platypus, 1.5 coils in the whale, 2.5–2.75 coils in man, and 3.0 coils in cats. Two membranes, the basilar membrane and Reissner’s membrane, extend along the inside of the cochlear canal and divide its cavity into three parts. These are the scala tympani; the scala vestibuli, which is filled with perilymph; and the scala media (cochlear duct), containing endolymph.

As a receptor of the auditory system, the cochlea transforms the acoustic energy of sound waves into energy stimulating the nerve fibers. The cochlea is also involved in the first stage of the frequency analysis of sound, a phenomenon based on spatial demarcation of the areas of the basilar membrane that are stimulated by sound frequencies.


Shmal’gauzen, I. I. Osnovy sravnitel’noi anatomii pozvonochnykh zhivotnykh, 4th ed. Moscow, 1947.
Titova, L. K. Razvitie retseptornykh struktur vnutrennego ukha pozvonochnykh. Leningrad, 1968.
Fiziologiia sensornykh sistem, part 2. (Rukovodstvo po fiziologii.) Leningrad, 1972.
Bioakustika. Moscow, 1975.



The snail-shaped canal of the mammalian inner ear; it is divided into three channels and contains the essential organs of hearing.


1. A tower for a spiral staircase.


the spiral tube, shaped like a snail's shell, that forms part of the internal ear, converting sound vibrations into nerve impulses
References in periodicals archive ?
MRI demonstrated T1-weighted hyperintensity and a complete loss of CISS signal in all three turns of the cochlea (figure 2, B), in the vestibule, and in the semicircular canals on the left.
It is interesting that our patient experienced a reversal of the loss of CISS signal in the middle and apical turns of his left cochlea between 2001 (figure 2, B) and 2006 (figure 2, C).
In this study, we detected little ROS formation in the cochleas of normal guinea pigs, and the signals of ROS were very weak.
The edaravone SLNs can inhibit ROS generation in cochleas after noise exposure and decrease hearing thresholds as measured by ABR.
The cochlea uses fluid mechanics, piezoelectrics and neural signal processing to convert sound waves into electrical signals that are sent to the brain.
The cochlea can perceive a hundredfold range of frequencies in humans, from 100 to 10,000Hz.
A Mathematical Model of an Artificial Cochlea Based on an Array of Resonators, Chapter 29 in DAAAM International Scientific Book 2009, pp.
From the CT images, Ketten's group made precise geometric measurements of all the cochleas and sent the images, drawings, and data to a research team led by Daphne Manoussaki, a mathematics professor at Vanderbilt University, and Richard S.
Cochlear implantation in children: labyrinthitis following pneumococcal otitis media in unimplanted and implanted cat cochleas.
At birth, the cochleas of rats are still quite immature, even though they already have formed most of their hair cells, she says.
Inside the cochlea reside microscopic hair cells that bend and, due to sound vibrations or changes in resistance, create electrical signals that are passed on to the auditory nerve and then to the brain.
Inside the cochlea, there are little hair cells that bend, sending an electrical current up the hearing nerve," he explained.