SCHWANNOMA DE NERVO VESTIBULAR, UMA REVISÃO BIBLIOGRÁFICA / VESTIBULAR NERVE SCHWANNOMA, A BIBLIOGRAPHIC REVIEW

The relationship between semicircular canal radius of curvature and afferent sensitivity has not been experimentally determined. We characterized mouse semicircular canal afferent responses to sinusoidal head rotations to facilitate interspecies and intraspecies comparisons of canal size to sensitivity. The interspecies experiment compared the horizontal canal afferent responses among animals ranging in size from mouse to rhesus monkey. The intraspecies experiment compared afferent responses from the larger anterior canal to those from the smaller horizontal canal of mice. The responses of mouse vestibular-nerve afferents showed a low- and high-frequency phase lead and high-frequency gain enhancement. Regular horizontal-canal afferents showed a sensitivity to 0.5-Hz sinusoidal rotations of 0.10 ± 0.03 (SD) spike · s−1/deg · s−1 and high-gain irregular afferents showed a sensitivity of 0.25 ± 0.11 spike · s−1/deg · s−1. The interspecies comparison showed that the sensitivity of regular afferents was related to the radius of curvature R according to the formula Gr = 0.23R − 0.09 ( r2 = 0.86) and the sensitivity of irregular afferents was related to radius according to the formula Gi = 0.32R + 0.01 ( r2 = 0.67). The intraspecies comparison showed that regularly firing anterior canal afferents were significantly more sensitive than those from the relatively smaller horizontal canal, with Gr = 0.25R. This suggests that canal radius of curvature is closely related to afferent sensitivity both among and within species. If the relationship in humans is similar to that demonstrated here, the sensitivity of their regular vestibular-nerve afferents to 0.5-Hz rotations is likely to be about 0.67 spike · s−1/deg · s−1 and of their high-gain irregular afferents about 1.06 spikes · s−1/deg · s−1.

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Inputs from regularly and irregularly discharging vestibular nerve afferents to secondary neurons in squirrel monkey vestibular nuclei. III. Correlation with vestibulospinal and vestibuloocular output pathways

Journal of Neurophysiology ◽

10.1152/jn.1992.68.2.471 ◽

1992 ◽

Vol 68 (2) ◽

pp. 471-484 ◽

Cited By ~ 78

Author(s):

R. Boyle ◽

J. M. Goldberg ◽

S. M. Highstein

Keyword(s):

Spinal Cord ◽

Transition Zone ◽

Vestibular Nucleus ◽

Vestibular Nuclei ◽

Vestibular Nerve ◽

Descending Pathways ◽

Relative Contribution ◽

Antidromic Stimulation ◽

Vestibulospinal Tract ◽

Irregular Afferents

1. A previous study measured the relative contributions made by regularly and irregularly discharging afferents to the monosynaptic vestibular nerve (Vi) input of individual secondary neurons located in and around the superior vestibular nucleus of barbiturate-anesthetized squirrel monkeys. Here, the analysis is extended to more caudal regions of the vestibular nuclei, which are a major source of both vestibuloocular and vestibulospinal pathways. As in the previous study, antidromic stimulation techniques are used to classify secondary neurons as oculomotor or spinal projecting. In addition, spinal-projecting neurons are distinguished by their descending pathways, their termination levels in the spinal cord, and their collateral projections to the IIIrd nucleus. 2. Monosynaptic excitatory postsynaptic potentials (EPSPs) were recorded intracellularly from secondary neurons as shocks of increasing strength were applied to Vi. Shocks were normalized in terms of the threshold (T) required to evoke field potentials in the vestibular nuclei. As shown previously, the relative contribution of irregular afferents to the total monosynaptic Vi input of each secondary neuron can be expressed as a %I index, the ratio (x100) of the relative sizes of the EPSPs evoked by shocks of 4 x T and 16 x T. 3. Antidromic stimulation was used to type secondary neurons as 1) medial vestibulospinal tract (MVST) cells projecting to spinal segments C1 or C6; 2) lateral vestibulospinal tract (LVST) cells projecting to C1, C6; or L1; 3) vestibulooculo-collic (VOC) cells projecting both to the IIIrd nucleus and by way of the MVST to C1 or C6; and 4) vestibuloocular (VOR) neurons projecting to the IIIrd nucleus but not to the spinal cord. Most of the neurons were located in the lateral vestibular nucleus (LV), including its dorsal (dLV) and ventral (vLV) divisions, and adjacent parts of the medial (MV) and descending nuclei (DV). Cells receiving quite different proportions of their direct inputs from regular and irregular afferents were intermingled in all regions explored. 4. LVST neurons are restricted to LV and DV and show a somatotopic organization. Those destined for the cervical and thoracic cord come from vLV, from a transition zone between vLV and DV, and to a lesser extent from dLV. Lumbar-projecting neurons are located more dorsally in dLV and more caudally in DV. MVST neurons reside in MV and in the vLV-DV transition zone.(ABSTRACT TRUNCATED AT 400 WORDS)

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Histologic Findings in Two Very Small Intracanalicular Solitary Schwannomas of the Eighth Nerve

Annals of Otology Rhinology & Laryngology ◽

10.1177/000348948609500505 ◽

1986 ◽

Vol 95 (5) ◽

pp. 460-465 ◽

Cited By ~ 11

Author(s):

J. Gail Neely ◽

Jack Hough

Keyword(s):

Nerve Fiber ◽

Longitudinal Direction ◽

Nerve Fibers ◽

Vestibular Nerve ◽

Cochlear Nerve ◽

The Other ◽

En Bloc ◽

Hearing Conservation ◽

Eighth Nerve ◽

Conservation Surgery

Two very small intracanalicular tumors, resected en bloc with the complete eighth nerve, were serially sectioned in order to study the relationship between the tumors and the nerves of origin. Both cases met the size criteria for hearing conservation surgery; however, the patient with the smaller tumor and the better hearing had no recognizable cochlear nerve fibers passing the tumor. The cochlear nerve in the patient with poorer hearing was completely free of tumor. The tumor with the infiltrated cochlear nerve seemed to originate from the inferior vestibular nerve. The other tumor seemed to arise from the superior vestibular nerve. Proximally, the tumors occupied a more central location in the involved nerves, but they abruptly became eccentric and exophytic as they proceeded laterally. Nerve fibers remaining about the tumors were displaced to the periphery. These nerve fiber aggregates became quite thin and attenuated, frequently separating into smaller aggregates which, ultimately, were incorporated into the tumors. As fibers came closer to the tumors, they tended to change from their longitudinal direction toward a more circumferential orientation about the surface of the tumors. The tumor-nerve fiber interfaces were quite variable throughout the course of the tumor, ranging from large aggregates of nerve fibers distinctly separate from the tumors to aggregates separate but tightly applied to the tumors without a tissue plane between, to aggregates partially incorporated within the periphery of the tumors, to aggregates completely incorporated into the periphery of the tumors. Frequently several types of interfaces were seen in the same section. These findings showed that in one case the cochlear nerve could have been surgically separated from the acoustic tumor; in the other specimen, it could not have been separated. It was impossible to predict between the two. In these two very small tumors, the gross specimen observation correlated reasonably well with the histology, thus suggesting that intraoperative observation may be a predictor in hearing conservation surgery; however, previous studies in slightly larger tumors make this an extremely guarded concept.

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Sensoritopic and Topologic Organization of the Vestibular Nerve

The Mammalian Cochlear Nuclei ◽

10.1007/978-1-4615-2932-3_35 ◽

1993 ◽

pp. 437-449 ◽

Cited By ~ 1

Author(s):

Vicente Honrubia ◽

Larry F. Hoffman ◽

Anita Newman ◽

Eri Naito ◽

Yasushi Naito ◽

...

Keyword(s):

Vestibular Nerve

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Inputs from regularly and irregularly discharging vestibular nerve afferents to secondary neurons in the vestibular nuclei of the squirrel monkey. II. Correlation with output pathways of secondary neurons

Journal of Neurophysiology ◽

10.1152/jn.1987.58.4.719 ◽

1987 ◽

Vol 58 (4) ◽

pp. 719-738 ◽

Cited By ~ 84

Author(s):

S. M. Highstein ◽

J. M. Goldberg ◽

A. K. Moschovakis ◽

C. Fernandez

Keyword(s):

Spinal Cord ◽

Vestibular Nucleus ◽

Preceding Paper ◽

Vestibular Nuclei ◽

Vestibular Nerve ◽

Antidromic Activation ◽

Mean Values ◽

Postsynaptic Potentials ◽

The Mean ◽

Vestibular Nerve Afferents

1. Intracellular recordings were made from secondary neurons in the vestibular nuclei of barbiturate-anesthetized squirrel monkeys. Monosynaptic excitatory postsynaptic potentials (EPSPs) evoked by stimulation of the ipsilateral vestibular nerve (Vi) were measured. An electrophysiological paradigm, described in the preceding paper (26), was used to determine the proportion of irregularly (I) and regularly (R) discharging Vi afferents making direct connections with individual secondary neurons. The results were expressed as a % I index, an estimate for each neuron of the percentage of the total Vi monosynaptic input that was derived from I afferents. The secondary neurons were also classified as I, R, or M cells, depending on whether they received their direct Vi inputs predominantly from I or R afferents or else from a mixture (M) of both kinds of Vi fibers. The neurons were located in the superior vestibular nucleus (SVN) or in the rostral parts of the medical or lateral (LVN) vestibular nuclei. 2. Antidromic activation or reconstruction of axonal trajectories after intrasomatic injection of horseradish peroxidase (HRP) was used to identify three classes of secondary neurons in terms of their output pathways: 1) cerebellar-projecting (Fl) cells innervating the flocculus (n = 26); 2) rostrally projecting (Oc) cells whose axons ascended toward the oculomotor (IIIrd) nucleus (n = 27); and 3) caudally projecting (Sp) cells with axons descending toward the spinal cord (n = 13). Two additional neurons, out of 21 tested, could be antidromically activated both from the level of the IIIrd nucleus and from the spinal cord. 3. The Vi inputs to the various classes of relay neurons differed. As a class, Oc neurons received the most regular inputs. Sp neurons had more irregular inputs. Fl neurons were heterogeneous with similar numbers of R, M, and I neurons. The mean values (+/- SD) of the % I index for the Oc, Fl, and Sp neurons were 34.7 +/- 24.7, 51.9 +/- 30.4, and 61.8 +/- 18.0%, respectively. Only the Oc neurons had a % I index that was similar to the proportion of I afferents (34%) in the vestibular nerve (cf. Ref. 26). 4. The commissural inputs from the contralateral vestibular nerve (Vc) also differed for the three projection classes. Commissural inhibition was most common in Fl cells: 22/25 (88%) of the neurons had Vc inhibitory postsynaptic potentials (IPSPs) and 1/25 (4%) had a Vc EPSP. In contrast, Vc inputs were only observed in approximately half the Oc and Sp neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

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