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Results for “Cochlear Nerve”

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At least 1,225 records · Page 68Linked to original sources
PubMed1992

Rapid changes in protein synthesis and cell size in the cochlear nucleus following eighth nerve activity blockade or cochlea ablation.

Destruction of the cochlea causes secondary changes in the central auditory pathway through transynaptic regulation. These changes appear to be mediated by an activity-dependent process and can be detected in the avian auditory system as early as 30 minutes after deafferentation. We compared the early changes in cochlear nucleus neurons following deafferentation by cochlea ablation with those seen following activity deprivation by perilymphatic tetrodotoxin (TTX) exposure. Protein synthesis and size of large spherical cells in the anteroventral cochlear nucleus (AVCN) of 14-day-old gerbils were measured during the first 48 hours after the manipulations. Both cochlea ablation and TTX produced a reliable decrease in protein synthesis by AVCN neurons (30-40%) by 1 hour. The magnitude of change in tritiated leucine incorporation was similar at all survival times, in both experimental groups. In contrast to the rapid changes in protein synthesis, the decrease in cell size was first evident 18 hours after TTX exposure and 48 hours after cochlea ablation. There was no significant change in protein synthesis or cell size in control groups at any of the survival times. These findings are consistent with changes in the avian auditory system in response to deafferentation and TTX exposure. Cochlea ablation and TTX exposure induced similar transneuronal changes, supporting the hypotheses that activity of auditory afferents in young mammals plays a regulatory role in the metabolism and morphology of their target neurons in the central auditory pathway, and that early changes following destruction of the peripheral receptor are due to reduction of activity-dependent interactions of presynaptic and postsynaptic cells.

Analysis of Variance↗
PubMed1994

Facial nerve stimulation produced by cochlear implants in patients with cochlear otosclerosis.

Thirty-eight adult cochlear implants have been performed at the University of Minnesota. Facial nerve stimulation by the implant in response to sound has been noted in four of these cases. Three of the four were patients whose sensorineural hearing loss was caused by cochlear otosclerosis. In each case it was possible to place the electrodes, however multiple leads had to be deprogrammed in order to avoid facial nerve stimulation. In each case characteristic radiographic findings of cochlear otosclerosis could be identified on preoperative temporal bone computed tomography scans. Although facial nerve stimulation has been described as a complication of cochlear implantation, it has not been reported to be associated with cochlear otosclerosis. Postoperative programming of the implant may be limited by facial nerve stimulation. In some cases these limits may reduce the efficacy of the device. This possibility should be taken into account during preoperative counseling of patients with cochlear otosclerosis considering cochlear implantation.

Aged↗
PubMed1975

Davis-1961 revisited. Signal transmission in the cochlear hair cell-nerve junction.

In 1961, Hallowell Davis proposed the occurrence of the following general sequence of interrelated events in sense organs, in response to specific sensory inputs: (1) the generation of receptor potentials in the sensory cells; (2) chemical transmission across the synapses between hair cells and afferent dendrites; and (3) the triggering of postsynaptic generator potentials capable of eliciting the actual nerve action potentials. Although at the time of his writing there was no evidence for this hypothesis in the auditory organ, there is now good support for the occurrence of all three events and for their general importance in the sensory transduction process.

Acetylcholine↗
PubMed1994

Cochlear implantation and variation of facial nerve anatomy: a case report.

Cochlear implantation becomes more common with every passing year. Since adequate exposure of the round window requires a facial recess approach, facial nerve variation and anomalies could potentially alter the surgical approach significantly. We report the case of a patient with a variation of facial nerve anatomy. The nerve was found to be lateral to the annulus in its mastoid segment and required retrofacial dissection to approach the round window. A good result was achieved in this patient, demonstrating that facial nerve anomalies need not be a barrier to successful implantation. The reported congenital anomalies of the facial nerve are discussed, along with their influence on cochlear implantation. A knowledge of these variations is mandatory for those engaged in implant surgery.

Adult↗
PubMed2004

Distribution of anterogradely labeled trigeminal and auditory nerve boutons on abducens motor neurons in turtles: implications for in vitro classical conditioning.

A conditioned abducens nerve response is generated in in vitro brainstem preparations from turtles by pairing a weak conditioned stimulus (CS) applied to the auditory nerve that immediately precedes an unconditioned stimulus (US) applied to the trigeminal nerve. Tract-tracing studies showed direct projections from auditory and trigeminal nerves to abducens motor neurons. In light of these findings for convergent CS-US inputs, it is hypothesized that auditory and trigeminal nerve synaptic inputs onto abducens motor neurons are in spatial proximity because the CS is a weak input that may be required to be near the US inputs to have an associative effect, and conditioning occurs only when the CS and US are temporally separated by less than 100 ms. This study examined the spatial relationship of 133 anterogradely labeled synaptic boutons conveying CS or US information on retrogradely labeled abducens motor neurons. The results show that trigeminal and auditory nerve terminal fields occupy primarily the soma and proximal dendrites of abducens motor neurons. Quantitative analysis shows that the majority of labeled boutons (76% and 85% from injections of the trigeminal and auditory nerves, respectively) were apposed to somata or were localized to dendritic segments no more than about 30 microm from the nucleus. There were no quantitative differences between trigeminal and auditory nerve boutons in terms of their localization on dendrites or bouton diameter. Finally, triple labeling experiments demonstrated that individual abducens motor neurons receive inputs from both nerves and that these inputs may be in close spatial proximity to one another. This synaptic arrangement allows for the possibility that in vitro abducens conditioning is generated by coincident CS-US detection mediated by NMDA receptors and may utilize a Hebbian-like plasticity mechanism.

Abducens Nerve↗
PubMed1982

Interaural crosstalk in the cat.

The physiologically effective interaural acoustic crosstalk in cat was measured by means of binaural threshold differences for single auditory-nerve fibers and for cochlear microphonics. There were generally two maxima, at about 800 Hz and 3 kHz, attaining values as high as -25 dB (transmission to cochlea via contralateral ear re transmission via ipsilateral ear) in some cats. This figure could be reduced to -50 dB by mechanically isolating the acoustic drivers from each other and from the stereotaxic head frame.

Animals↗
PubMed1981

Eighth nerve alcoholic neuropathy: a case report with light and electron microscopic findings.

A 55-year-old man with symptoms of hearing loss, balance disturbance, and facial weakness was treated by translabyrinthine eighth cranial nerve trans-section. The patient also had a history and physical signs of chronic alcoholism and peripheral polyneuropathy. Results of laboratory tests revealed concomitant nutritional deficiency. Histopathological examination of the eighth nerve showed extensive degeneration of both myelinated and unmyelinated nerve fibers in both cochlear and vestibular divisions. Light and electron microscopic features of the degenerative process were compatible with previously described pathology of experimentally induced Wallerian-like degeneration. Alcoholic neuropathy as the cause of hearing loss and balance disturbance--and probably facial paresis--is suggested.

Alcoholism↗
PubMedDate not supplied

Renewal-process approximation of a stochastic threshold model for electrical neural stimulation.

In a recent set of modeling studies we have developed a stochastic threshold model of auditory nerve response to single biphasic electrical pulses (Bruce et al., 1999c) and moderate rate (less than 800 pulses per second) pulse trains (Bruce et al., 1999a). In this article we derive an analytical approximation for the single-pulse model, which is then extended to describe the pulse-train model in the case of evenly timed, uniform pulses. This renewal-process description provides an accurate and computationally efficient model of electrical stimulation of single auditory nerve fibers by a cochlear implant that may be extended to other forms of electrical neural stimulation.

Action Potentials↗
PubMed1999

The perceptual effects of current pulse duration in electrical stimulation of the auditory nerve.

In cochlear implants employing pulsatile stimulation, loudness is controlled by current amplitude and/or pulse duration. Five experiments were conducted with cochlear implantees to investigate the hypothesis that perceptual effects other than loudness result from changes in pulse duration for durations from 50 to 266 microseconds. In experiment 1, five subjects' ability to discriminate equally loud pulse trains employing differing pulse durations was measured at four electrode positions. In 11 of the 20 cases, subjects could significantly discriminate these stimuli. In experiments 2 and 3, discrimination was measured of dual-electrode stimuli which differed in overall temporal pattern but had an equal temporal pattern on each of the individual electrodes (separated by 0 to 9 mm). Discrimination was compared for stimuli employing short or long pulse durations and, in experiment 3, employing different pulse durations on each electrode. When the pulse duration was longer, six out of seven subjects could either combine temporal information across electrode positions at wider electrode separations (experiment 2) or had better discrimination at the same electrode separation (experiment 3). This result was consistent with the hypothesis that longer pulse durations result in a greater spread of excitation than equally loud stimuli using shorter pulse durations. In experiment 4, pulse rate discrimination was compared for stimuli with differing pulse durations, and in four out of five subjects, there was no effect of pulse duration. Finally, the dB change in current per doubling of pulse duration for threshold and equally loud stimuli was calculated for nine subjects (52 electrodes). Values ranged from -5.9 to -2.0 dB/doubling, and were significantly correlated with the absolute intensity of the stimulus. This result was hypothesized to be due to a relationship between the neural charging characteristics and the distance of the excited neural elements from the electrode.

Adult↗