Cochlear Canal Research Articles

A flexible micromachined electrode array for a cochlear prosthesis

A micromachined silicon electrode array intended for use as a cochlear implant is reported. The flexible array is formed using a boron etch-stop for substrate definition and contains 22 IrO stimulating sites implemented on 750 μm centers. The insertable portion of the array is 25 mm long and 320–640 μm in width; the back end of the device provides interconnects to implanted current-generation circuitry. Device functionality has been verified through in vivo experiments and the associated evoked auditory brainstem responses are reported; thresholds for monopolar stimulation are less than 80 μA. The integration of polysilicon strain gauges on the array will permit monitoring of implant curvature within the cochlea, providing a resolution in substrate position of 60 μm across the 500 μm diameter cochlear canal.

An X-radiographic and SEM study of the osseous inner ear of multituberculates and monotremes (Mammalia): implications for mammalian phylogeny and evolution of hearing

Multituberculate petrosals with well-preserved, three-dimensional internal anatomy from the Late Cretaceous/early Paleocene Bug Creek Anthills, Montana, U.S.A., are described from X-radiographic and SEM images, as well as from conventional visual observations, and are compared with the anatomy of the osseous inner ear in monotremes and in primitive non-therian and therian mammals. Results of this study indicate that: (1) the cochlea of at least some multituberculates retained a lagena, previously known only in monotremes among mammals; (2) an enlarged vestibule evolved in several lineages of multituberculates independently, and hence is not a synapomorphy of the order; (3) the cochlear canal lacks osseous laminae in support of the short, wide basilar membrane, which was probably inefficient in responding to high-frequency airborne vibrations; and (4) consequently, bone-conducted hearing in some multituberculate species may have been important in interpretation of their surroundings. Comparisons with the inner ear of monotremes and primitive therians indicate that curvature of the cochlea and cribriform plates for passage of vestibulocochlear nerve branches through the petrosal are unlikely homologues between monotremes and therians. From non-therian to therian mammals, there is a distinct morphological gap in the inner ear transition, characterized by acquisition of a number of neomorphs in the therian inner ear; an intermediate stage has yet to be discovered.

An X-radiographic and SEM study of the osseous inner ear of multituberculates and monotremes (Mammalia): implications for mammalian phylogeny and evolution of hearing

Multituberculate petrosals with well-preserved, three-dimensional internal anatomy from the Late Cretaceous/early Paleocene Bug Creek Anthills, Montana, U.S.A., are described from X-radiographic and SEM images, as well as from conventional visual observations, and are compared with the anatomy of the osseous inner ear in monotremes and in primitive non-therian and therian mammals. Results of this study indicate that: (1) the cochlea of at least some multituberculates retained a lagena, previously known only in monotremes among mammals; (2) an enlarged vestibule evolved in several lineages of multituberculates independently, and hence is not a synapomorphy of the order; (3) the cochlear canal lacks osseous laminae in support of the short, wide basilar membrane, which was probably inefficient in responding to high-frequency airborne vibrations; and (4) consequently, bone-conducted hearing in some multituberculate species may have been important in interpretation of their surroundings. Comparisons with the inner ear of monotremes and primitive therians indicate that curvature of the cochlea and cribriform plates for passage of vestibulocochlear nerve branches through the petrosal are unlikely homologues between monotremes and therians. From non-therian to therian mammals, there is a distinct morphological gap in the inner ear transition, characterized by acquisition of a number of neomorphs in the therian inner ear; an intermediate stage has yet to be discovered.

Petrosal (periotic) and inner ear of a Pliocene kogiine whale (Kogiinae, Odontoceti): implications on relationships and hearing evolution of toothed whales

ABSTRACT This study describes the petrosal (periotic) bone and the inner ear of a fossil pygmy sperm whale (Kogiinae, Physeteridae, Cetacea) from the Yorktown Formation (Pliocene) of the Lee Creek Mines of North Carolina. A cladistic analysis of 36 petrosal characters among 18 cetacean taxa shows that extant and fossil kogiines are diagnosed by a plate-like and posteriorly oriented posterior process of the petrosal. The Physeteridae is diagnosed by two petrosal apomorphies: presence of an incudal process for the articulation of the incus, and an enlarged accessory ossicle. Petrosal apomorphies suggest that physeterids and ziphiids are sister groups among the odontocetes, and that the Mysticeti and Odontoceti are both monophyletic. The cochlear spiral of the Pliocene kogiine petrosal has two full turns and a cochlear basal/height ratio of 0.6. Within the cochlear canal, the secondary bony lamina for the basilar membrane is present in one and one-quarter turns of the cochlea. The width of the basilar membra...

Evolutionary Origins of The Mammalian Promontorium and Cochlea

ABSTRACT Mammals have two apomorphies in the ear region: an elongated cochlear canal and an eminence on the tympanic side of the cochlear housing, known as the petrosal promontorium. In nonmammalian cynodonts, the cochlear recess is shorter, smaller, and oriented more medially than the mammalian cochlear canal; their cochlear housing is formed by the prootic, opisthotic, and basisphenoid. New fossil materials of two early mammals, Adelobasileus and Sinoconodon, reveal evidence on the evolutionary transformation of the mammalian cochlear canal and bony cochlear housing. Adelobasileus is more derived than any known non-mammalian cynodont in possessing an incipient promontorium, but more primitive than other mammals in retaining a vestigial basisphenoid wing. Sinoconodon has a fully developed petrosal promontorium but a short cochlea that extends only one third of the promontorium length. The cochlear canal of Morganucodon is twice as long as that of Sinoconodon, relative to both skull and promontorium. More derived mammals, such as Haldanodon and multituberculates, have an even longer cochlear canal. We propose that the promontorium transformed by expansion of the petrosal bone at the expense of the basisphenoid (probably also the basioccipital) through the transition from non-mammalian cynodonts to mammals. This change in ossification of the cochlear housing resulted in a re-orientation of the cochlea and a better acoustic insulation of the inner ear. The mosaic of a fully developed promontorium and a short cochlear canal in Sinoconodon suggests that the formation of the promontorium preceded (and thus may be necessary for) the elongation of the mammalian cochlea.

Therian Petrosals From the Oldman and Milk River Formations (Late Cretaceous), Alberta, Canada

ABSTRACT Therian petrosals from the Milk River and Oldman formations of Alberta are described. The Milk River specimen is the earliest known ear structure of a therian from North America and has a cochlea with one and a quarter turns. Two of the Oldman specimens are from marsupials, probably Eodelphis. These specimens provide significant new evidence about the earliest known otic structures in marsupials, including: absence of the promontory and stapedial grooves on the promontorium, presence of a prominent rostral tympanic process of the petrosal, achievement of a fully coiled cochlear canal, and development of the radial innervation system of the cochlea. Implications of the new findings are: 1) absence of the stapedial artery is consistently distributed in marsupials; 2) the rostral tympanic process of the petrosal has evolved more than once in marsupials; 3) a fully coiled cochlear canal had evolved in the therian ear by the Late Cretaceous; 4) a radial innervation complex of the cochlea evolved along with the coiled cochlea in the therian ear during the Late Cretaceous.

Ultrastructural and Immunocytochemical Study of the Subepithelial Fiber Component of the Guinea Pig Inner Ear

The connective tissues of the lateral cochlear wall and semicircular canal of the guinea pig were investigated by transmission electron microscopy, intermediate voltage electron microscopy and immunocytochemistry. In the spiral ligament, numerous fibroblasts and fiber bundles were intermingled with each other. Fibroblasts and fibers were also observed in the semicircular canal. Ultrastructurally, immuno-gold particles, indicating the presence of type II collagen, were found on the fibers in the spiral ligament and the semicircular canals. The present results revealed that both stria vascularis and the membranous semicircular canal were supported by a network of fibroblasts and type II collagen fibers.

Fiberoptic argon laser stapedotomy with annular ligament reconstruction

The goal of stapes surgery is to restore normal physiologic vibration of the fluids within the cochlear canal. For optimum results, both the acoustic impedance transfer of the ossicular chain and the acoustic impedance of the annular ligament should be restored. The article reviews a cohort of over 2,200 cases of stapedial otosclerosis successfully operatedon by fiberoptic argon laser stapedotomy with annular ligament vein reconstruction technique. The results are presented.

N-myc expression in the embryonic cochlea of the mouse

N-myc expression in the mouse embryo was examined during the late cochlear organogenesis. Tissue distribution of N-myc expression was histologically analyzed by in situ hybridization of the transcript in the cochlea between 15 and 18 days of gestation. At 15 days of gestation, N-myc expression was found very conspicuous in nervous structure of the cochlea such as the auditory nerve and the spiral ganglion. Moreover, N-myc was also present in the Köllikers organ and in the epithelium surrounding the cochlear canal. A few days later, N-myc expression was still clearly present in the Köllikers organ but less so in nervous structures. This study shows that cochlear tissues derived from the otic placode present a significant level of N-myc transcript during late embryogenesis. N-myc expression seems to be related to cell differentiation in the inner ear.

CT scanning and computerized reconstructions of the inner ear of multituberculate mammals

ABSTRACT The inner-ear structure of four multituberculate petrosals from the Late Cretaceous and Early Paleocene of North America was examined with computerized tomography (CT). Transverse CT scan images of these petrosals were digitized to produce a three-dimensional reconstruction of the acousto-vestibular spaces of multituberculates. Our investigation shows that the acousto-vestibular spaces of multituberculates are characterized by a straight cochlear canal and an extraordinarily enlarged vestibular cavity. Comparison of multituberculate inner-ear structures with those in other major mammalian clades suggests that the cochlea of multituberculates, which is similar to that of Morganucodon, is more derived than the cochlea of non-mammalian therapsids but more primitive than the coiled cochlea of therian and monotreme mammals. The extraordinary inflation of the vestibule of multituberculates is a uniquely derived character of most Cretaceous and Tertiary multituberculates, and it may be the synapomorphy ...

Micro-architectures of the osseous spiral laminae and spiral limbus in the mouse cochlea: a scanning electron microscopic study on the morphological basis of the auditory mechanics.

The auditory mechanics in the cochlea are closely related to the structural variations along the cochlear duct. In this study, the auditory teeth of the spiral limbus and the primary and secondary osseous spiral laminae in the mouse were examined along the entire course of the cochlear spiral by scanning electron microscopy (SEM) after removing the cochlear duct epithelium or the organic material with chemical maceration methods. The cochlear canal consisted of a hook and a spiral of one and half turns and the three-dimensional images and surface structures of the connective tissue forming the spiral limbus including the auditory teeth and the osseous spiral laminae are well demonstrated; the widths of the primary and secondary laminae, the spiral fissure between the two laminae, the tympanic lip, and the vestibular lip with the auditory teeth were measured, and the population density of the auditory teeth were determined in the hook and every half turn. The findings suggest that, in the cochlea the width of the basilar membrane increases in the hook and is almost constant in the spiral portion, the amount of fibers in the basilar membrane linearly decreases from the base to the apex, the displacement mode of the pillar cells during basilar membrane vibrations differs between the apical region lacking the bony edge of the tympanic lip and the other regions with bony edge, the connective tissue fibers from the auditory teeth are inserted to the bone surface of the primary lamina to support the teeth, the teeth on the marginal side of the vestibular lip maintain the stability of the tectorial membrane which is vibrating together with the basilar membrane in response to high frequency sounds on the basal side of the cochlear duct and low frequencies on the apical side, and the interdental cells on the Reissner membrane side maintain the size of the tectorial membrane which shows a linear increase in size from the base to the apex of the cochlear duct.

Ototoxicity of ethanol in the tympanic cleft in animals.

This work was undertaken to study the ototoxicity of topically applied ethanol in quantitative terms. Using guinea pigs, ethanol was administered (1) on the round window for 10 min, (2) instilled in the middle ear cavity for 24 hours, and (3) perfused into the cochlear canal (into the scala tympani) at the rat of 10 microliter/min for 10 min. Cochlear microphonics from the electrode on the round window were recorded. The critical concentration (the maximum dilution ratio) of the ethanol that appears to be ototoxic in the experimental condition mentioned above was determined to be (1) 50%, (2) 10%, (3) 0.1% respectively. Using chinchillas, the effect of ethanol with round window application on the Endocochlear Potential (EP) was studied. Simultaneous recording of EP from the 1st and 3rd turn of the cochlea showed a more marked decline in EP in the 1st turn. 70% ethanol caused an irreversible, plateauing decline in EPO, while 35% ethanol caused a reversible decline in EP.

Visualization of canaliculus cochleae by multidirectional tomography.

A technique for tomographic visualization of the cochlear canal is given. This technique implies a possibility, preoperatively, of singling out patients in whom an abnormally wide cochlear canal may be the cause of perilymphatic fistulization in connection with stapedectomies.

MORPHOLOGICAL STUDY ON THE MEMBRANOUS LABYRINTH OF THE COCHLEA BY MEANS OF A PHASE CONTRAST MICROSCOPE

By the use of a phase contrast microscope, the author examined the structure of fresh memb-ranous labyrinth of guinea pig.Observations were summarised as fallows:1) The inner and outer hair cells and their supporting cells were respectively separated from Organ of Corti by means of micro-surgical technique, and their fine structures were observed.2) The bassilar, reticular, tectorial and Reissner's membarnes and vascular stria were respectively separated from cochlear canal. Their constructions were observed.3) Particularly, hairs of sensory cells were examined in detail. It might be stated from this observation that the forms and distribution of hairs are different in respective portions of the spiral turn of cochlea.The anthor concluded from the mor phological observation described above, that the hairs of sensory cells play an important role in the analytic mechanism of sound frequency in the inner ear.

The Variation of Phase Along the Basilar Membrane with Sinusoidal Vibrations

An optical means of measuring phase relations in the cochlea is described. With the stapes set into sinusoidal vibration, the phase relations, measured along the length of the cochlear partition, show that a traveling wave has been set up. The form of resonance which appears does not correspond at all with that to be found in a simple vibrating system. Measurements are presented for a frequency of 200 c.p.s. of the amplitude and phase of vibration at various places along the cochlear partition. From these is derived a curve showing the longitudinal bending of the partition with the traveling wave at two different points in time. Very small changes in the form of vibration can easily be demonstrated by the measurements of phase. By this means it is shown that the basilar membrane cannot be released from tension since it is not normally under tension. The elastic properties of the various distinguishable tissues within the cochlear partition were measured. These measurements show that only the elasticity of the basilar membrane changes through the length of the cochlear canal. The other portions of the partition are quite constant throughout the entire distance. Further, the non-linearity in the vibration of the partition was investigated with results which indicate that the observed lowering of pitch of a tone when the loudness is increased cannot be produced by mechanical means.