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Results for “SEMICIRCULAR CANALS”

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PubMed1999

Semicircular canal and saccular influence on the subjective visual horizontal during gondola centrifugation.

Measurements of the subjective visual horizontal (SVH) were performed in 11 healthy test persons during an increase of the resultant gravitoinertial force vector in a large swing-out gondola centrifuge. Three levels of hypergravity (1.5 g, 2.0 g, 2.5 g) were used, each with a duration of 4 minutes and with 1-2 minute pauses at 1.0 g in between. The direction of the resultant gravitoinertial force vector was always parallel with the head and body length axis. Hence, there was no roll stimulus to the otolith organs. The swing-out of the gondola during acceleration, however, is sensed by the vertical semicircular canals as a change in roll head position, thus creating an otolith-semicircular canal conflict. After acceleration of the centrifuge there was a tilt of the SVH relative to the resultant gravitoinertial horizontal. This tilt gradually decayed during the 4-minute period of recordings. For a subgroup of seven test subjects who had completely normal ENG-recordings in 1 g environment, the initial offset of SVH and the time constants for exponential decay were determined for each g level; initial offsets: 9.9 degrees (1.5 g), 7.7 degrees (2.0 g), 6.1 degrees (2.5 g); time constants: 89s (1.5 g), 74s (2.0 g), 37s (2.5 g). The offset of SVH is interpreted as being the result of mainly the stimulus to the vertical semicircular canals during acceleration of the centrifuge. The slow decay, however, does not correspond to the dynamics of the semicircular canal system, and is suggested to reflect some kind of central position storage mechanism. A smaller offset and more rapid decay for the higher g loads may be explained by an increasing dominance of graviceptive input, presumably from the saccules. In conclusion, these results might suggest the role of the vertical semicircular canals as well as the sacculus in the formation of SVH. They may also have relevance with regard to the spatial disorientation problem in aviators.

Adult↗

PubMedDate not supplied

Semicircular canal structure during postnatal development in cat and guinea pig.

The gain of the vestibulo-ocular reflex in the cat continues to increase for some time after birth. The reason for this increase is not presently known and one possibility if that it occurs because the cat semicircular canals increase in size. The present study examined this possibility by measuring the radii of curvature (R) of individual semicircular canals and the angular relationships of the semicircular canal planes within a labyrinth in cats and guinea pigs during postnatal growth. It was found that the labyrinths do move apart substantially during postnatal development in both species, but neither the planar relations nor the radii of curvature change significantly during postnatal development. The stability of semicircular canal structure during postnatal skull growth indicates that postnatal developmental changes in canal-related function, such as increased gain in the vestibulo-ocular reflex, in these species are probably due to receptor cell or neural maturational factors.

Animals↗

PubMed2000

[Establishment of the animal model of triple semicircular canal occlusion].

OBJECTIVE: To establish the animal model of triple semicircular canal occlusion(TCO) in guinea pigs. METHODS: TCO was performed on 20 guinea pigs. Electronystagmography, auditory brainstem responses (ABR) and distortion product otoacoustic emissions(DPOAE) were recorded pre- and post-operatively. The non-operated ear was used as control. RESULTS: There was spontaneous nystagmus towards non-operated side on the 1st postoperative day and no nystagmus to stimuli of sinusoidal angular acceleration in operated side. On the 30th postoperative day, left and right nystagmus returned symmetrical. Pre-operation, ice-water stimulation induced normal symmetric nystagmus in both sides. On the 30th postoperative day, ice-water stimulation only induced normal nystagmus in non-operated ear and failed in operated one. ABR thresholds increased approximately 10 dB post-operation. There were no significant changes of the amplitudes of DPOAE before and after surgery. Histologic examination revealed complete occlusion in the three semicircular canals with newly formed bone and connective tissue. CONCLUSION: This study showed that the animal model of TCO was successfully established. These findings suggests that TCO might be a safe and simple procedure for the treatment of intractable peripheral vertigo.

Animals↗

PubMed2006

The primate subarcuate fossa and its relationship to the semicircular canals part I: prenatal growth.

Studies have reported a functional link between the arc size of the semicircular canals and locomotor agility across adult primates. However, canal size is spatially interlinked with the subarcuate fossa. This fossa can house the petrosal lobule of the paraflocculus, which also plays a role in coordinating head and eye movements. Consequently, it could be that it is the size of the petrosal lobule and fossa that are directly associated with locomotor agility, and not canal arc size. The apparent association of the latter would only follow from the spatial requirement of the canals to accommodate a suitably enlarged subarcuate fossa and petrosal lobule. This study aims to test the ontogenetic basis of this argument by examining high-resolution magnetic resonance images of fetal samples of Homo sapiens, Macaca nemestrina, and Alouatta caraya. Falsifiable null hypotheses examined are (1) that development of the subarcuate fossa is initiated by growth of the petrosal lobule, and (2) that growth of the semicircular canals and of the subarcuate fossa are independent. The findings confirm that the subarcuate fossa forms independently of a petrosal lobule in all three species, thereby falsifying the first hypothesis. Significant correlations were observed between size variables of the semicircular canals and the subarcuate fossa, particularly between the anterior canal and the opening of the fossa. These results falsify the hypothesis that the canals and fossa grow entirely independently. In the human sample, canal growth outpaces fossa growth, possibly because no petrosal lobule is present in humans. In the other two species, the subarcuate fossa simply seems to fill the space made available by canal growth. However, fossa enlargement cannot be excluded as an influence on size increase in the canals. Nevertheless, taken together, the results suggest that canal size is unlikely to be determined primarily by the spatial requirements of the subarcuate fossa and petrosal lobule, rather than by sensory demands reflected in the empirically established link with locomotor agility.

Adult↗

PubMed2003

"Step by step" treatment of lateral semicircular canal canalolithiasis under videonystagmoscopic examination.

Aim of the work was to describe a new physical therapeutic approach for benign paroxysmal positional vertigo determined by canalolithiasis of the lateral semicircular canal. A review is made of the literature, and personal experience is reported. A total of 55 cases were observed, 40 geotropic forms, 15 apogeotropic forms. Liberatory manoeuvres were carried out observing the nystagmus during videonystagmoscopic examination, thus attempting to solve the problem in the first treatment session. Monitoring the patient under videonystagmoscopic examination, progression of the otolithic mass towards the non-ampullary segment is documented by the appearance of a nystagmus directed towards the healthy side (and, therefore, inhibitory, due to ampullofugal deflection of the ampullary cupula) during the individual steps of the rehabilitation treatment. Of the 40 geotropic forms, 30 were successfully treated with the Vannucchi-Asprella technique, and the other 10 with the Vannucchi-Asprella manoeuvre followed by a Lempert barbecue rotation. Of the 15 apogeotropic forms, 6 were solved with the Vannucchi-Asprella manoeuvre, 2 with the Vannucchi-Asprella technique followed by Lempert, 6 with the inverted Gufoni technique, followed by Lempert, 1 transformed into geotropic with inverted Gufoni plus Lempert and then resolved by means of a Vannucchi-Asprella manoeuvre. In all cases, therapeutic success was achieved in the first session. Treatment of benign paroxysmal positional vertigo of the lateral semicircular canal does not allow every case to be fully solved at the first attempt with any technique proposed up to now, in particular, for the apogeotropic forms. Being aware of the different techniques, choosing that most appropriate for the patient's "physical" needs, and, above all, verifying under videonystagmoscopic examination the progression in an ampullofugal direction of the otolithic mass during treatment enable excellent therapeutic results to be obtained in the treatment of benign paroxysmal positional vertigo of the lateral semicircular canal, by modifying the rehabilitation strategy while it is being carried out. Videonystagmoscopic examination monitoring of the nystagmus during treatment of benign paroxysmal positional vertigo of the lateral semicircular canal, is taking the place of the rigid schematism of the manoeuvres proposed, so far, allowing the treatment programme to be adapted to the individual case, thus enabling a solution to be reached in the first rehabilitation session by means of tailored therapy.

Humans↗

PubMed1991

Hyaluronan as a propellant for epithelial movement: the development of semicircular canals in the inner ear of Xenopus.

The membranous labyrinth of the inner ear, with its three semicircular canals, originates from a simple spheroidal otic vesicle. The process is easily observed in Xenopus. The vesicle develops three dorsal outpocketings; from the two opposite faces of each outpocketing pillars of tissue are protruded into the lumen; and these paired 'axial protrusions' eventually meet and fuse, to form a column of tissue spanning the lumen of the outpocketing like the hub of a wheel, with a tube of epithelium forming the semicircular canal around the periphery. Each axial protrusion consists of epithelium encasing a core of largely cell-free extracellular matrix that stains strongly with alcian blue. In sections, at least 60% of the stainable material is removed by treatment with Streptomyces hyaluronidase. When Streptomyces hyaluronidase is microinjected into the core of a protrusion in vivo, the protrusion collapses and the corresponding semicircular canal fails to form. Hyaluronan (hyaluronic acid) in the core of the protrusion therefore seems to be essential in driving the extension of the protrusion. Autoradiography with tritiated glucosamine indicates that the hyaluronan-rich matrix is synthesised by the epithelium covering the tip of the protrusion; the basal lamina here appears to be discontinuous. These findings indicate that the epithelium of the axial protrusion propels itself into the lumen of the otocyst by localised synthesis of hyaluronan. Hyaluronan may be used in a similar way in the development of other organs, such as the heart and the secondary palate.

Animals↗

PubMed1979

The development of function of horizontal semicircular canal primary neurons in the rat.

The activity of primary horizontal semicircular canal neurons in newborn rats was compared to similar cells in adults. All animals were anesthetized with ether. Neurons were categorized as regular or irregular on the basis of their spontaneous activity. Horizontal semicircular canal neurons can respond to angular acceleration stimulation at birth. In newborn rats no regularly firing cells could be found, but the percentage of these cells and their average resting rate increased during growth. Neurons in newborn rats differ from those in the adult by having a lower average resting rate, a lower sensitivity to long-duration angular acceleration and taking longer to reach peak increase in firing during the stimulus. Sensitivity reaches adult values by about 4 days although the canal dimensions continue to increase until about 20 days.

Afferent Pathways↗

PubMed1999

Superior semicircular canal dehiscence: a new cause of vertigo.

There are many known causes of vertigo, but many cases remain unexplained. Sound-induced, pressure-induced, or positional vertigo caused by bony dehiscence of the superior semicircular canal into the middle cranial fossa is a newly described etiology of vertigo. Three case studies of patients with CT evidence and surgical confirmation of bony dehiscence of the superior semicircular canal with variable presentations are described. The history, symptoms, CT findings, vestibular studies, and method of surgical repair are presented. Two patients had disabling vertigo and one had no vestibular symptoms. All underwent exploration via a middle cranial fossa approach with repair of the dehiscence. The bony dehiscence of the superior semicircular canal of the asymptomatic patient was identified and closed at the time of an encephalocele repair procedure. All patients did well postoperatively and both patients with vertigo improved. Bony dehiscence of the superior semicircular canal may cause vertigo or be asymptomatic and should be added to the differential diagnosis of vertigo.

Bone Cements↗

PubMed1976

Damped pendular rotation nystagmus after unilateral labyrinthectomy or unilateral lateral semicircular canal block in squirrel monkeys.

Using a damped pendular rotation table, which provided an oscillation of 15.5 sec, per-rotatory nystagmus, was evaluated in six squirrel monkeys that underwent unilateral labyrinthectomy and five that underwent unilateral lateral semicircular canal block, both pre- and postoperatively. The bidirectional summation of the nystagmic slow-phase eye speed after unilateral labyrinthectomy and after unilateral lateral semicircular canal block showed similar reduction to about 60 per cent of the values obtained in the pre-operative status. Under the present test situation, both slow-phase eye speed and number of nystagmic beats in the monkeys after unilateral lateral semicircular canal block were larger by the ampullopetal stimulation than those evoked by ampullofugal stimulation. The relation between slow-phase eye speed and number of beats showed similar tendency when we compared pre-operative controls and the group after unilateral lateral semicircular canal block, but the monkeys after unilateral labyrinthectomy depicted different tendencies.

Animals↗

PubMed1983

Fracture studies on a mammalian semicircular canal.

In the present work the pressures necessary to fracture the semicircular canal of the mammalian inner ear, specifically the squirrel monkey, have been investigated experimentally. The results indicate that individual canals can fracture when subjected to internal pressures of approximately 1.6 +/- 0.4 MPa. Simulation testing using Plexiglas and polycarbonate specimens, to represent the location of a possible osteoclast site within the bone forming a semicircular canal, demonstrates further that fracture of the canal can be initiated at this or even lower pressures when the pressure is generated within a simulated osteoclast site. These results provide useful information for a better understanding of the mechanisms by which bubble nucleation and growth could cause pressures of this magnitude within an osteoclast cavity during the decompression phase of a diving schedule.

Animals↗

PubMed2002

[Angles between left and right vertical semicircular canals].

To clarify anatomical relationships between the left and right vertical semicircular canal (SCC), we measured angles between the left and right posterior SCCs, and angles between left and right anterior SCCs. Subjects were T2 images of axial magnetic resonance imaging (MRI) in 50 patients reporting headaches. The mean angle between the left and right posterior SCC was 92.6 degrees (S.D. = 11.7) and that between the left and right anterior SCC was 76.1 degrees (S.D. = 10.4). These results suggest that angles between the left and right vertical semicircular canals are not always 90 degrees, and interindividual differences in the relationship between canal planes are great, indicating a need for discretion in analyzing peripheral nystagmus.

Adolescent↗

PubMed1996

Determinants of semicircular canal afferent response dynamics in fish.

Present results separate the relative contributions of semicircular canal biomechanics from hair cell/afferent biophysics in determining the amplitude and phase of afferent responses to sinusoidal motion of the head. Separation was achieved by combining electrical polarization of the endolymph with mechanical indentation of the canal limb to modulate the instantaneous firing rate of horizontal semicircular canal afferents. The electrical stimulus drives hair cell transduction currents via modulation of the Nernst-Planck potential, whereas the mechanical stimulus mimics head rotation and modulates the open probability of the transduction channels. Responses for electrical polarization therefore reflect post-transduction-current (PTC) mechanisms, and responses for mechanical stimulation include the additional influence of canal mechanics. Linear transfer functions defining individual afferent response dynamics were obtained for low levels of each stimuli and are reported in Bode form providing gain (spikes/s per micron or mV) and phase (deg re: peak stim) over the frequency range from 0.02 to 40 Hz. Combined results for electrical and mechanical stimuli distinguish the component of sensory signal processing carried out by canal mechanics from that carried out by the hair cell/afferent complexes. Individual afferents were categorized according to their response to the mechanical stimuli as low-gain velocity (LG), high-gain velocity (HG) or acceleration (A) sensitive, groups as originally defined by Boyle and Highstein to describe interafferent diversity present within the population. In contrast to the results for mechanical stimuli, all afferent groups exhibit nearly equal increases in gain and phase for increasing frequencies of electrical stimulation. Comparison of individual afferent responses for the two stimuli leads to the conclusion that the LG, HG, and A groups are distinguished primarily by diversity in the mechanical activation of associated hair cells and not by PTC mechanisms. Even though PTC processing does not contribute significantly to determining these groups, it is the primary determinant underlying high-frequency gain and phase enhancements observed in the population average. Comparison of mechanical and electrical responses also reveals the mechanical lower-corner responsible for phase enhancements and gain decreases in all afferents at low frequencies of mechanical stimulation (< 0.05 Hz). Results imply that LG afferents encode angular head velocity by canceling a phase lag and gain attenuation due to the mechanics with a phase lead and gain enhancement due to PTC mechanisms above approximately 0.2 Hz. In contrast, A group afferents encode angular head acceleration by combining high-frequency phase leads and gain enhancements present in both the mechanics and PTC mechanisms across the physiological frequency spectrum. HG afferents fall between these two extremes, and, other than the influence of the mechanical lower-corner, their response primarily reflects PTC processing.

Action Potentials↗

PubMed1990

The ultrastructure of the supporting system in the guinea pig semicircular canal.

The ultrastructure of the perilymphatic space of the guinea pig semicircular canal was examined, using thin sectioning, scanning electron microscopy and freeze-fracture methods. The perilymphatic space was divided into two parts: an area of fibrous matrix and an area of fibroblasts with bundles of fine filaments. In the area of fibroblasts, cell processes and filament bundles formed a meshed pattern. The cell processes were interconnected with each other by both intermediary and gap junctions. The inner surface of the osseous semicircular canal was covered with multilayers of cell processes of both fibroblasts and mesothelial cells. The fact that tight and gap junctions were observed between the cell processes suggests a functional significance in these structures.

Animals↗

PubMed1991

Effect on cochlear potentials of lateral semicircular canal destruction.

Recording of the cochlear potentials was successfully performed during experimental labyrinthectomy in the guinea pig and in three patients with acoustic neuromas during translabyrinthine removal of the tumors. In the guinea pig, complete interruption of the duct of the lateral semicircular canal including the endolymphatic canal caused little change in the endocochlear DC potential of the first cochlear turn and input-output function curve of the N1 component of the compound action potential elicited by 8-kHz tone bursts. Further drilling of the vestibular labyrinth in the guinea pig caused decline of these potentials when the vestibular was opened. In patients with acoustic neuromas, the interruption of the duct of the lateral semicircular canal hardly altered the N1 input-output function curve and N1 input-latency function curve during the 1-hour observation period. Consistent preservation of cochlear function even after interruption of lateral semicircular canals suggests the possibility of partial surgical labryrinthectomy with preservation of hearing for lesions involving semicircular canals.

Acoustic Stimulation↗

PubMed2000

Netrin 1 is required for semicircular canal formation in the mouse inner ear.

The morphogenetic development of the mammalian inner ear is a complex multistep process, the molecular and cellular details of which are only beginning to be unraveled. We show here that mouse netrin 1, known to be involved in axon guidance and cell migration in the central nervous system, also plays a critical morphogenetic role during semicircular canal formation. netrin 1 is expressed at high levels in the otic epithelium, in cells that will come together to form a fusion plate, a prerequisite for the formation of semicircular canals. In netrin 1 mutant mice, fusion plate formation is severely affected resulting in a reduced anterior semicircular canal and the complete lack of the posterior and lateral canals. Our results suggest that netrin 1 facilitates semicircular canal formation through two different mechanisms: (1) it participates in the detachment of the fusion plate epithelia from the basement membrane, and (2) it stimulates proliferation of the periotic mesenchymal cells which then push the epithelial cell walls together to form the fusion plate.

Alleles↗

PubMed1986

Production of endolymph in the semicircular canal of the frog Rana esculenta.

The mechanisms of secretion of endolymph were studied in vitro in the isolated inner ear of the frog. Prior to in vitro experiments, the composition of perilymph was evaluated in vivo and compared to that of plasma. Composition of perilymph resembled that of an extracellular fluid, although Na and Cl concentrations were higher and K concentration was lower in perilymph than in plasma water. No difference in Ca and Mg concentrations was observed between these two fluids. Osmolality averaged 227 mosmol/kg H2O in perilymph and 183 mosmol/kg H2O in plasma. Endolymph in frog inner ear corresponded in chemical pattern to mammalian endolymph. K and Na concentrations in endolymph collected from the ampulla of the posterior vertical semicircular canal averaged 121.1 mM and 2.5 mM, respectively. Osmolality of endolymph was 237 mosmol/kg H2O. K and Na concentrations were unaltered when inner ears were incubated for 24 h either at 15 degrees C or at 4 degrees C. Addition of ouabain (10(-4) M) to the perilymph-like bathing solution altered greatly Na and K composition of endolymph after incubation for 3 h at 15 degrees C. The Na and K concentration gradients between endolymph and the bath were abolished after incubation for 24 h. Ligatures of the posterior vertical semicircular canal were performed at different sites to isolate some parts of the canal, i.e. the ampulla and the non-ampullar duct. K concentration in the ampulla after incubation for 24 h remained as high as 20 times that in the bath. This K gradient was abolished in the presence of ouabain (10(-4) M). High K concentration could be maintained in the non-ampullar part of the semicircular canal only if the latter communicated with the ampulla. It is concluded that endolymph is actively secreted into the ampulla of the semicircular canal. Na+-K+-activated ATPase in the ampullar dark cells may energize the ouabain sensitive ionic transports that are involved in the production of endolymph. Endolymph secreted into the ampulla would spread intraluminally to account for the high K and low Na concentrations of the fluid which fills the non-secretory part of the semicircular canal.

Animals↗

PubMed1989

Responses of pigeon horizontal semicircular canal afferent fibers. II. High-frequency mechanical stimulation.

1. The horizontal semicircular canals of anesthetized (barbiturate/ketamine) pigeons were mechanically stimulated by the use of a piezoelectric micropusher that provided controlled indentation of the surgically exposed membranous horizontal semicircular duct. 2. Extracellular action potentials from single horizontal semicircular canal afferent (HCA) fibers were recorded during sinusoidal mechanical stimulation. This method of stimulation was shown in the companion paper to produce equivalent responses to those produced by rotation for frequencies ranging from 0.01 to 10 Hz. 3. Sinusoidal mechanical stimulation produced clearly entrained action potentials in some HCA fibers up to a frequency of 400 Hz (highest stimulus frequency tested), with stimulus probe displacements of +/- 1.0 and +/- 2.5 microns. Thirty-four HCA fibers were thoroughly studied. 4. For most HCA fibers, the number of action potentials per stimulus cycle decreased as stimulus frequency increased, until only one action potential per stimulus cycle was elicited. The point at which only one spike per stimulus cycle was observed was dependent on both the fiber's resting mean discharge rate (MDR) and the fiber's coefficient of variation (CV) obtained during the MDR. 5. Dynamic response properties of individual HCA fibers were found to be correlated with the fiber's CV and the resting level MDR. Neurons with lower CV values had less adaptation, higher short time constants, and lower high corner frequencies than did neurons with high CV values. For a given CV class of HCA fibers, neurons with higher MDRs had more enhanced gains and more advanced phase shifts at high stimulus frequencies than did neurons with lower MDRs. 6. Transfer function parameters affecting the dynamics of the high-frequency response were derived from the mean gain and phase shift values of regular-, intermediate-, and irregular-firing HCA fibers. Best-fit short time constant (tau S) values of 4.6, 1.9, and 2.0 ms; hair cell membrane time constant (tau M) values of 10.3, 13, and 7 ms; excitatory postsynaptic membrane time constant (tau E) values of 0.8, 0.4, and 0.5 ms; and synaptic delay time constant (tau D) values of 0.5, 0.5, and 1.4 ms were determined for regular, intermediate, and irregular classes of HCA fibers, respectively. 7. The values of 4.6, 1.9, and 2.0 ms derived for the regular, intermediate, and irregular afferents would suggest upper-corner frequencies of 35, 84, and 80 Hz for these classes of HCA fibers, respectively.

Animals↗

PubMed2000

Spatial distribution of semicircular canal nerve evoked monosynaptic response components in frog vestibular nuclei.

Most second-order vestibular neurons receive a canal-specific monosynaptic excitation, although the central projections of semicircular canal afferents overlap extensively. This remarkable canal specificity prompted us to study the spatial organization of evoked field potentials following selective stimulation of individual canal nerves. Electrically evoked responses in the vestibular nuclei were mapped systematically in vitro. Constructed activation maps were superimposed on a cytoarchitectonically defined anatomical map. The spatial activation maps for pre- and postsynaptic response components evoked by stimulation of a given canal nerve were similar. Activation maps for monosynaptic inputs from different canals tended to show a differential distribution of their peak amplitudes, although the overlap was considerable. Anterior vertical canal signals peaked in the superior vestibular nucleus, posterior vertical canal signals peaked in the descending and in the dorsal part of the lateral vestibular nucleus, whereas horizontal canal signals peaked in the descending and in the ventral part of the lateral vestibular nucleus. A similar, differential but overlapping, spatial organization of the canal inputs was described also for other vertebrates, suggesting a crude but rather conservative topographical organization of semicircular canal nerve projections within the vestibular nuclei. Differences in the precision of topological representations between vestibular and other sensory modalities are discussed.

Animals↗