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Results for “Cochlear Nerve”

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At least 19 recordsLinked to original sources

PubMed1978

Pathologic features of the cochlear nerve in profound deafness.

Cochlear nerves transected in the internal meatus were studied in six totally deaf ears and in one ear with profound deafness. In five ears deafness had followed surgical procedures in the oval window, in one it was the result of a mumps infection, and one was probably due to a virus infection or a vascular lesion. In four cases there was no great reduction in the nerve fiber population and the ultrastructure appeared normal. In three nerves there was a reduction in the number of nerve fibers, interfibrillar fibrosis, and disorganized material or extensive degenerative changes in the myelin sheaths. In all specimens artificial myelin changes were seen that apparently resulted from manipulation of the specimens at removal. Analysis of these cochlear nerves suggests that retrograde degeneration after severe cochlear insults may not be as frequent as has been thought on the basis of animal studies.

Adult↗

PubMed1978

Neural correlates of auditory fatigue: frequency-dependent changes in activity of single cochlear nerve fibers.

1. These experiments were designed to test whether intense pure tones produced greater depression of cochlear nerve fibers tuned to the exposure frequency or of those tuned to frequencies above the exposure frequency. Spike discharges of single fibers were studied in anesthetized cats before, during, and after exposures lasting 1 min. Exposure frequency was varied relative to each fiber's characteristic frequency (CF), and was either at the CF or 1/2 octave above (+1/2 oct) or 1/2 octave below (-1/2 oct) the CF. Exposure levels were 85 or 90 dB SPL. Effects of the various exposures on driven discharge rates were evaluated using standard test stimuli at each fiber's CF. In addition, nonevoked discharges were measured during the brief quiet intervals between test stimuli ("interstimulus activity") as well as during extended quiet periods ("resting activity"). Major results were as follows: 2. All the exposures resulted in depression of the driven discharge rates; however, these effects were strongly dependent on the exposure frequency. The depression was greatest and endured the longest following -1/2 oct exposures at 90 dB. The CF exposures at 85 and 90 dB were much less depressant, as were exposures at -1/2 oct at 85 dB; these three exposures resulted in very similar recovery functions. The +1/2 oct exposures produced little or no depression, whether at 85 or 90 dB. 3. Interstimulus activity was depressed immediately following all exposures, but recovered to normal quickly than did driven discharge rates. Following exposures at -1/2 oct at 90 dB, recovery was non-monotonic in that an extended period of supernormality preceded the return to normal rates. During this period of elevated activity, the interstimulus activity approached but never exceeded the resting rate of the same fiber. 4. Resting activity recovered even more rapidly than interstimulus activity, being completely normal by 1 min following all exposures. 5. These results constitute the first demonstration that the CF is not necessarily the most depressant exposure frequency for a given cochlear nerve fiber. Further, the results imply that the half-octave (or greater) shifts of the point of maximum hearing loss, so characteristic of auditory fatigue, may be accounted for by frequency-dependent alterations in the responsiveness of cochlear nerve fibers.

Acoustic Stimulation↗

PubMed1978

Temporal and spatial sequence of anterograde degeneration in the cochlear nerve fibers of the cat. A light microscopic study.

This study deals with anterograde degeneration in the cochlear nerve fibers following cochlear lesions. The observations are based on 2-mum thick sections of material embedded in resin according to procedures used in electron microscopy and stained with toluidine blue. Among the various operative approaches used in this study, sparing of the modiolus afforded the least local reaction and furnished the material best suited for anterograde degneration studies in this nerve only 2 mm long. The anterograde degeneration of the cochlear nerve is characterized by segmental swelling of myelinated nerve fibers followed by shrinkage of the axoplasm and collapse of the distended myelin sheaths. The swelling, which begins at the nodal-paranodal region of the axon, is preceded by accumulation in the cytoplasm of granular organelles, presumably mitochondria and lysosomes. The portions of the cochlear fibers situated in the nerve root, i.e., within the cochlear nuclei and including the axon terminals, follow essentially the same pattern of degeneration as those in the peripheral portion of the nerve. Both peripherally and centrally degenerative changes occur first in the basal, high frequency fibers and centrally degenerative changes occur first in the basal, high frequency fibers and progress to the apical, low frequency fibers. The difference between the two extremes in the onset of degeneration is, approximately, 24 hours. Once initiated, however, the pace of degeneration is the same along the whole fiber spectrum.

Animals↗

PubMed1978

The cochlear nerve in the cat: topography, cochleotopy, and fiber spectrum.

The topographical and cytological features of the cochlear nerve in normal adult cats were studied by microdissection, light microscopy, transmission and scanning electron microscopy. The 2-mm long cochlear nerve trunk is situated within the internal acoustic meatus. The nerve is wrapped like a roll with the more basal fibers situated peripheral to the more apical ones. The fibers are fasciculated according to their target in the cochlea and follow a helical course with the sharpest spiralling in the distal portion of the fiber. Apical and basal coil fibers are of approximately the same length measured from the spiral lamina to the rostral border of the anteroventral cochlear nucleus. The nerve contains about 90% thick, myelinated fibers, about 10% unmyelinated axons, and a few thin, but heavily myelinated axons. The first group shows a unimodal distribution of axonal diameters, with a gradual increase in average diameter from basal to apical coil fibers. The number of axonal microtubules and neurofilaments have a high linear correlation to axonal circumference without principal cochleotopic differences. The myelin sheaths are thicker and the internodal segments shorter than expected from similarly sized peripheral fibers in rodents. The possible nature and origin of the three fiber categories are discussed.

Animals↗

PubMed1979

Auditory potentials of cochlear nerve and brain stem in multiple sclerosis.

Auditory evoked potentials of the cochlear nerve and the brain stem were recorded in ten patients with multiple sclerosis (MS) and four patients thought to possibly have MS. A characteristic pattern materialized, with a prolonged N1-P4 conduction time and absent or small N2 and/or N5 waves. We discuss possible clinical implications.

Adult↗

PubMed1978

Cochlear nerve in neurilemomas. Audiology and histopathology.

Correlative data between the histopathologic changes in the cochlear nerve and audiologic findings are reported in 16 cases of neurilemomas. Poor speech discrimination, positive or absent recruitment, excessive adaptation, or separation of forward vs reverse continuous tone Bekesy tracings did not correlate with the number of preserved nerve fibers. There were several cases with profound hearing loss in which the nerve fiber population approached normal. Histologically, pathologic changes included dilated fibers and increased interfibrillary collagen. In many specimens the fibers were further apart than normally, especially in the immediate vicinity of the tumor, and many lay between tumor cells. The tumor-nerve interface was usually gradual and no abrupt change appeared at the transition from the nerve to the tumor, the Schwann cells appearing to continue as tumor cells. Nonspecific changes apparently due to specimen handling were seen in some areas of most specimens.

Adult↗

PubMed1978

Cochlear travelling wave velocities calculated from the derived components of the cochlear nerve and brainstem evoked responses of the human auditory system.

From the latency difference between corresponding components of the different derived cochlear nerve and brainstem evoked responses (CBER) and the cochlear location difference between the appropriate derived band centre frequencies (CF), estimates of the travelling wave velocity at various locations along the cochlear partition were calculated. Calculated velocities compared favourably with velocity data obtained using widely contrasting techniques. Derived CBER waveforms were therefore considered to truly represent neural activity initiated by activity at specific frequency regions along the cochlear partition.

Audiometry, Evoked Response↗

PubMed1976

Cochlear nerve degeneration coincident with adrenocerebroleukodystrophy.

A 19-month-old boy had adrenocerebroleukodystrophy and unusually severe cochlear nerve degeneration and demyelination, a condition in advance of that expected from known disease entities. We report the only known temporal bone study in adrenocerebroleukodystrophy.

Adrenoleukodystrophy↗

PubMed1978

Derived cochlear nerve and brainstem evoked responses of the human auditory system. The effect of masking in the derived band.

Derived cochlear nerve and brainstem evoked responses (CBER) were obtained for various frequency bands and were masked using special maskers. These maskers were designed to match exactly the intensity/frequency profile characteristics of the bands from which derived CBERs were obtained. Derived responses were markedly affected whenever the masker frequency limits coincided with the corresponding derived band. Other derived responses from adjacent bands were not affected. Since adjacent derived bands overlap, these overlapping regions were not considered to be represented in the derived responses. Therefore the actual frequency regions which the derived responses represented were considered to be smaller than the derived bands calculated from the physical parameters of the high-pass masking noises.

Brain Stem↗

PubMed1978

Frequency specific components of the cochlear nerve and brainstem evoked responses of the human auditory system.

A technique of high-pass (HP) masking was used to obtain masked cochlear nerve and brainstem evoked responses (CBER) of the human auditory system. The masking noise was extended progressively into the lower frequency regions of the cochlea for consecutively recorded responses, and the effect upon the response waveform was observed. Masked response waveforms were then subtracted to produce derived CBER waveforms representing activity initiated at specific frequency locations along the cochlear partition. Derived response components from various frequency bands were characterized and related to changes in the complex CBER during the process of frequency selective high-pass masking.

Adult↗

PubMedDate not supplied

Cochlear nerve projections following organ of corti destruction.

Experimental organ of Corti destruction results in (1) secondary loss of all type I spiral ganglion neurons, (2) development of type III spiral ganglion neurons, (3) degeneration of most cochlear nerve myelinated fibers, and (4) terminal degeneration in the ventral and dorsal cochlear nuclei. The first signs of degenerative changes occur by eight days after organ of Corti destruction and degeneration debris remains until 28 weeks after destruction.

Animals↗

PubMed1978

The validity of the derived cochlear nerve and brainstem evoked responses of the human auditory system.

It was considered that for a number of reasons, the derived response concept might not necessarily be valid when applied to the cochlear nerve and brainstem evoked responses (CBER). A statistical comparison of response measures of amplitude and latency was made between derived and non-derived responses, each representing response contributions initiated by the same locations along the cochlear partition. Relatively few statistical differences were detected. Therefore the technique of waveform summation and the production of derived response waveforms from complex responses, recorded under appropriate masking conditions, was considered to be a valid operation.

Brain Stem↗

PubMed1975