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Results for “VESTIBULAR APPARATUS”

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At least 451 records · Page 25Linked to original sources

PubMed2005

Contouring the middle and inner ear on radiotherapy planning scans.

The purpose of this study was to establish guidelines that help radiation oncologists contour the inner and middle ear on treatment planning scans. The radiotherapy computed tomography (CT) scans of 15 previously treated patients were reviewed for the ability to identify 3 separate auditory structures. The middle ear, the cochlea, and the vestibular apparatus were identified and contoured on each scan using anatomic landmarks. The volume and maximum axial dimension of each contour were calculated. The middle ear, cochlea, and vestibular apparatus were identified on all scans. The middle ear was defined by the tympanic membrane laterally and by the interface between air and the temporal bone in all other directions. The plane of the internal auditory canal through the temporal bone was the landmark distinguishing the vestibular apparatus from the cochlea. The mean volume of the middle ear, vestibular apparatus, and cochlea were 0.58 cm3, 0.44 cm3, and 0.14 cm3, respectively. The maximum axial dimension across the contour averaged 1.57 cm for the middle ear, 1.10 cm for the vestibular apparatus, and 0.69 cm for the cochlea. A reference atlas was constructed that shows the contour of each structure on 5 consecutive CT images. Accurate identification of the middle ear and inner ear structures on radiotherapy planning scans is possible and is necessary if critical auditory organs are to be spared during radiotherapy of targets that are located near the base of the skull. The information generated in this study will help radiation oncologists contour auditory structures accurately.

Ear, Inner↗

PubMed2002

Consequences and assessment of human vestibular failure: implications for postural control.

Labyrinthine afferents respond to both angular velocity (semicircular canals) and linear acceleration (otoliths), including gravity. Given their response to gravity, the otoliths are likely to have an important role in the postural functions of the vestibular apparatus. Unilateral vestibular ablation has dramatic effects on posture in many animals, but less so in primates. Nevertheless, bilateral vestibular lesions lead to disabling symptoms in man related to disturbed ocular and postural control and impaired perception of slopes and accelerations. While seimicircular canal function can be assessed through its effects on vestibular ocular reflexes, assessment of otolith function in man has traditionally been much more difficult. Recent definition of a short latency vestibulocollic reflex, activated by sound and appearing to arise from the saccule, shows promise as a new method of non-invasive assessment of otolith function.

Animals↗

PubMed2001

Postural reflexes evoked by tapping forehead and chest.

We investigated whether a tap with a reflex hammer to the forehead can elicit responses in the leg muscles and whether vestibular stimulation is the crucial prerequisite for eliciting these responses. We also measured the postural changes caused by the tap and by the compensatory, presumably reflex-like reactions of the subject. Tap-evoked activity of leg muscles was easily elicited during upright stance in normal subjects and was also seen in two subjects without vestibular function. The pattern of muscle activation clearly showed a counteraction to the tap-evoked perturbation of stance. Taps applied to the chest elicited similar reflexes. Since these two conditions imply a different activation of the vestibular apparatus, the vestibular input alone cannot account for the observed leg muscle reflexes. We suggest that multisensory reflex pathways that integrate vestibular and proprioceptive inputs account for these reflexes.

Adult↗

PubMed1994

The influence of middle ear pressure changes on the primary vestibular neurons in guinea pigs.

The responses of primary vestibular neurons and perilymphatic pressure changes to middle ear pressure stimuli in guinea pigs were investigated in order to clarify the direct effects of pressure stimulus on the vestibular apparatus. The vestibular response was related to the amount of middle ear pressure change applied at a rate of +/- 100 mmH2O/s. The neural response rates of vestibular units to positive pressure in the middle ear were significantly larger than those to negative pressure. The time course pattern of the perilymphatic pressure change resembled that of the response of the vestibular units, indicating that the vestibular response is elicited by middle ear pressure via the pressure transmitted in the inner ear.

Animals↗

PubMedDate not supplied

Experimental perilymphatic fistula.

Perilymphatic fistula was produced in guinea pigs by injecting artificial perilymph into the subarachnoid space of the posterior fossa. Rupture of the round window was confirmed by direct observation of the round window membrane under a surgical microscope during the injection. The animals were either vitally fixed or kept alive for one to three months before fixation. Conventional celloidin embedding method was used for serial sectioning. In immediate observation, nine cochleas showed hydrops, seven showed collapse, and 20 of 36 cochleas showed no change. Changes in the vestibular apparatus varied, with collapse of the membranous vestibular labyrinth as the main change. Delayed observation revealed 16 normal cochleas and four collapses and no hydrops out of 20 ears. Of these 20, nine ears showed normal vestibular apparatus, nine collapse, and two saccule hydrops. Loss of the outer hair cells was observed in five of 20 cochleas. Marked compression of the organ of Corti was seen in both immediate and delayed observations.

Animals↗

PubMed2005

Development and evolution of the vestibular sensory apparatus of the mammalian ear.

Herein, we will review molecular aspects of vestibular ear development and present them in the context of evolutionary changes and hair cell regeneration. Several genes guide the development of anterior and posterior canals. Although some of these genes are also important for horizontal canal development, this canal strongly depends on a single gene, Otx1. Otx1 also governs the segregation of saccule and utricle. Several genes are essential for otoconia and cupula formation, but protein interactions necessary to form and maintain otoconia or a cupula are not yet understood. Nerve fiber guidance to specific vestibular end-organs is predominantly mediated by diffusible neurotrophic factors that work even in the absence of differentiated hair cells. Neurotrophins, in particular Bdnf, are the most crucial attractive factor released by hair cells. If Bdnf is misexpressed, fibers can be redirected away from hair cells. Hair cell differentiation is mediated by Atoh1. However, Atoh1 may not initiate hair cell precursor formation. Resolving the role of Atoh1 in postmitotic hair cell precursors is crucial for future attempts in hair cell regeneration. Additional analyses are needed before gene therapy can help regenerate hair cells, restore otoconia, and reconnect sensory epithelia to the brain.

Animals↗

PubMedDate not supplied

Experimental study of some features of the etiology and pathogenesis of motion sickness.

A study was made of vestibular stability in man as affected by acceleration in various directions and of acceleration affecting receptors of the vestibular apparatus with varying frequency. It was established that tolerance for vestibular stimulation in certain individuals may be affected by direction of acceleration and frequency of the action. Individual susceptibility to motion sickness is widely expressed under conditions of specific vestibular stimulation. The results obtained indicate that development of motion sickness does not depend on the activity of the vestibular analyzer and motion sickness is not its specific vestibular reaction. Motion sickness is a reaction of the whole organism and its manifestation under long stimulation of receptors of the vestibular apparatus in individuals predisposed to motion sickness depends on specific features of the activity of the limbico-reticular complex.

Acceleration↗

PubMed1999

Structural basis for mechanical transduction in the frog vestibular sensory apparatus: III. The organization of the otoconial mass.

The saccule and the utricle of the vestibular system detect linear acceleration and gravity. Sensory transduction in these organs depends on myriads of calcium carbonate crystals of high specific gravity, called otoconia, embedded in a filament matrix that overlies the sensory epithelium. The coexistence of hard crystals and slender filaments in this complex extracellular matrix makes it difficult to analyze by conventional electron microscopy. We have now examined this structure in the bullfrog saccule using the quick-freeze, deep-etch replica technique. The otoconia in their typical aragonite polymorph shape exhibit smooth surfaces and are embedded in a loose matrix made of two types of filaments. The regular surface of the otoconia forms a natural smooth background against which we could observe with unprecedented detail the network organization and substructure of the filaments. One type of filament is 8 nm in diameter, while the other, which has a characteristic beaded appearance, is 15 nm in diameter. Both types of filaments either make lateral connections with or end directly on the surface of the otoconia. A consistent observation was the presence of short filaments that directly cross-link adjacent otoconia. Very few otoconia were fractured in an orientation that would allow the study of their internal architecture. These otoconia presented a typical conchoidal cleavage of aragonite. Although crystallites were not clearly apparent, thin lamellar microstructures appeared oriented both perpendicularly and longitudinally to the major otoconial axis. This structural study establishes a framework for the identification of the molecular components present in this unique extracellular matrix and may also help elucidate their role in mechanical transduction.

Animals↗

PubMed1998

[Study of mechanisms underlying the effects of low-frequency acoustic vibrations].

The article covers experimental data about influence of infrasound on hearing and vestibular apparatus, about body changes linked functionally to this apparatus. The authors revealed 4 zones of response of hearing and vestibular apparatus to infrasound. Infrasound appeared to affect directly nuclei of VIII and X cranial nerves and indirectly other organs and systems linked functionally to vagus nerve.

Animals↗

PubMedDate not supplied

Audio-vestibular findings in patients with vestibular neuritis.

19 patients with the clinical diagnosis vestibular neuritis, i.e., cases with unilaterally ENG verified abolished or reduced caloric reactions but without symptoms of central nervous involvement or hearing impairment, participated in the study. In addition to ENG examinations and Békésy audiometry all patients were submitted to stapedius reflex tests and auditory brainstem response examinations (ABR) for signs of subclinical auditory nerve engagement. In all but one of the 19 patients the caloric reactions improved; 8 of the 13 patients available for tests after one year recovered completely. The ABR was normal in all cases but the stapedius reflex thresholds were pathologically elevated and remained so in about half of the subjects throughout the observation time; reflex decay was not present in anyone. Cases with pathologically elevated stapedius reflex thresholds showed a tendency to slower recovery of the vestibular function than the group with the normal reflexes. The results were interpreted to indicate lack of eighth nerve or CNS engagement. The possibility that subjects with reflex threshold elevation may constitute a group with constitutional weakness of the audio-vestibular apparatus disposed for vestibular disease is discussed.

Adult↗

PubMed2001

Impairments of vestibular system in infants at risk of early brain damage.

Children with early brain damage often present with balance disorders. We evaluated the vestibular apparatus function in 110 infants at risk of brain lesions. Our study confirmed a statistically significant correlation between vestibular apparatus dysfunction and the degree of neurological risk. Early recognition of vestibular disorders preconditions adequate rehabilatation and supports the acquisition of motor skills.

Brain Injuries↗

PubMed1990

[The effect of muscle relaxants on the function of the vestibulo-ocular reflex arc].

Baclofen affects in experiments the reactivity of the vestibuloocular reflex by influencing the time constant of the vestibular nystagmus. The authors compare in three healthy volunteers the reactivity of the vestibular apparatus after administration of Baclofen and a new muscle-relaxant drug tizanidine. The authors evaluate basic parameters of the vestibular and optokinetic nystagmus (gain and time constant), discuss the problem of GABAergic (Baclofen) and monoaminergic (tizanide) receptors kin the area of the vestibular apparatus. As regards the effect on the reactivity of the vestibular system, tizanidine does not affect immediately the response of the vestibuloocular reflex but interferes with processes ensured by the central neuronal integrator.

Adult↗

PubMed1975

[Influence of vestibular and afferent impulses on the spontaneous activity of interneurons in the spinal cord of cats].

Responses of the cat spinal interneurons were studied under electrical stimulation of dorsal roots and adequate stimulation of vestibular apparatus. The evoked activity of interneurons in response to electrical stimulation of dorsal roots had different forms. Three types of responses to adequate stimulation of vestibular apparatus were observed. The patterns of convergence of afferent and vestibular impulses on the interneurons are discussed.

Animals↗

PubMed1990

Structural basis for mechanical transduction in the frog vestibular sensory apparatus: I. The otolithic membrane.

The mechanical coupling of the otoliths to the hair cell sensory stereocilia at the surface of the vestibular sensory epithelium is mediated by two layers of extracellular matrix, each one with a specific role in the mechanical transduction process. The first is a rigid layer in direct contact with the otolithic mass and is known as the otolithic membrane or gelatin membrane. This structure consists of a dense, randomly cross linked filament network that uniformly distributes the force of inertia of the non-uniform otolithic mass to all stereocilia bundles. The second layer formed by a columnar organization of filaments secures the otolithic membrane above the surface of the epithelium. The long columnar filaments are organized in parallel to the stereocilia bundles and are anchored to the apical surface of the supporting cells. The zonula adherens at the apical region of each supporting cell displays a thick polygonal bundle of actin filaments forming at the surface of the epithelium a transcellular honeycomb organization that provides mechanical ground support for the columnar filament layer. The dominant aspect of this columnar filament layer indicates that it may also have an important role in attenuating the force of inertia of the large otolithic mass during acceleration, screening stresses that would be directed to an effective bending of the stereocilia bundles.

Animals↗

PubMedDate not supplied

Vestibular tests in the selection of cosmonauts.

Vestibulo-vegetative disorders in cosmonauts and astronauts occurring during space flight compel otolaryngologists to search for vestibular tests enabling a precise evaluation of the activity of the vestibular apparatus and showing disposition to motion sickness. Otoneurological investigation of Polish candidates for cosmonaut status consisted of the following vestibular tests: caloric, rotatory, optokinetic, swinging torsion, statokinesimetric and vestibulo-vegetative. The value of various vestibular tests for aviation and space medicine is presented in this paper, taking into account the results of investigations of the equilibrium system with the group of pilots selected for space flight as well as extensive experience with candidates for the air service and also trained pilots and patients. The relatively frequent lack of correlation between the results of the applied tests, which renders difficult the proper evaluation of the equilibrium system, is emphasized in the paper. Finally, the results of investigations of acute habituation of the vestibular apparatus are discussed.

Adult↗

PubMed1996

[Methodological bases of studying vestibular reactions].

The paper outlines the current concepts of the physiological functions of the vestibular system and identifies their contradictions. It suggests that from the standpoint of the theory of functional systems and, in the biocybernetic context, the vestibular apparatus should be regarded as an individual component of the whole static and kinetic system that ensures the coordination of movements, the function of the vestibular apparatus as part of the common afferent current and somatic, sensory, and autonomic reactions as the ultimate result of the whole system's activity.

Cybernetics↗

PubMed1980

Induced vestibular dysfunction in squirrel monkeys during rapid decompression.

The symptoms of postural instability and dizziness associated with decompression sickness could be ascribed to either damage of the vestibular apparatus or to central nervous system damage. However, a histological study of monkeys exposed to decompression reveals that these symptoms primarily result from damage to the vestibular apparatus (unless there are accompanying central deficits). Furthermore, the damage is of a type that causes new bone growth to occlude the otic fluid spaces of the semicircular canals. In some instances, there is sufficient bone growth to render the cristae ampullares as non-functional end organs. Such diminished vestibular function would present a serious threat to the diver.

Animals↗

PubMedDate not supplied

Nausogenic properties of various dynamic and static force environments.

Motion sickness can occur when an accelerating force acting on the human body repeatedly changes amplitude and direction or both. It also can occur without any motion after transfer into a constant force field significantly different from Earth-gravity. Dynamic and static causes of motion sickness can be distinguished accordingly. Space sickness, too, has dynamic as well as static aspects. Dynamic space sickness might depend on increased bilateral differential sensitivity of the peripheral and central vestibular apparatus, whereas static space sickness may be caused by erroneous compensation of bilaterial asymmetries of the otolith-system in the microgravity environment. Experiments in airplanes, cars and on a vestibular sled have shown that the susceptibility to motion sickness is highest for changes of acceleration in the negative X-axis (as compared to the other axes) of the body. During reciprocating linear accelerations on the vestibular sled, standstill periods of movement and the direction of movement cannot correctly be indicated, because the peripheral vestibular apparatus lacks true motion detectors.

Acceleration↗