Asymmetric cupula displacement due to endolymph vortex in the human semicircular canal

Biomechanics and Modeling in Mechanobiology - The vestibular system in the inner ear senses angular head manoeuvres by endolymph fluid which deforms a gelatinous sensory structure (the cupula). We...     

Numerical modeling and verification by nystagmus slow-phase velocity of the function of semicircular canals

Biomechanics and Modeling in Mechanobiology - The malfunctioning of semicircular canals (SCCs) in the vestibular system results in diseases that disrupt the individual’s daily life....     

Functional physiology of the semicircular canal ampulla.

Physiology of the semicircular canal (sc) was studied by applying different manipulations to the isolated frog sc. Function of the cupula was investigated by mapping out the mechanical sensitivity on the cupular surface and by removing and replacing the cupula. The cupula was found to be most essential for effective activation of sc receptors. Responses of sc receptors to direct temperature change were studied. The sc nerve discharge increased and decreased due to cool and warm temperature change respectively. This suggests a possibility of direct temperature effect as one of the mechanisms of caloric response.     

Theoretical aspects of cupula deflection in semicircular canal

The deflection of the sensory hairs produced by a given volumetric displacement of endolymph (ΔV) is compared in the two usually-accepted models of the cupula behavior: the watertight hinged flap and the elastic diaphragm. Developing the mathematics of these two models, it appears that the elastic diaphragm engenders a larger deflection of sensory hairs than the hinged flap, the difference being about twice in magnitude. Whatever the model, the angle of the cupular deflection is always proportional to the relative angular displacement of the endolymph during natural stimulations.     

Evolution of locomotion in Anthropoidea: the semicircular canal evidence

Our understanding of locomotor evolution in anthropoid primates has been limited to those taxa for which good postcranial fossil material and appropriate modern analogues are available. We report the results of an analysis of semicircular canal size variation in 16 fossil anthropoid species dating from the Late Eocene to the Late Miocene, and use these data to reconstruct evolutionary changes in locomotor adaptations in anthropoid primates over the last 35 Ma. Phylogenetically informed regression analyses of semicircular canal size reveal three important aspects of anthropoid locomotor evolution: (i) the earliest anthropoid primates engaged in relatively slow locomotor behaviours, suggesting that this was the basal anthropoid pattern; (ii) platyrrhines from the Miocene of South America were relatively agile compared with earlier anthropoids; and (iii) while the last common ancestor of cercopithecoids and hominoids likely was relatively slow like earlier stem catarrhines, the results suggest that the basal crown catarrhine may have been a relatively agile animal. The latter scenario would indicate that hominoids of the later Miocene secondarily derived their relatively slow locomotor repertoires.     

Temperature dependency of cupular mechanics and hair cell frequency selectivity in the fish canal lateral line organ

The mechanical frequency selectivity of the cupula located in the supraorbital lateral line canal and the frequency selectivity of the hair cells driven by the cupula were measured simultaneously in vivo. Laser interferometry was used to measure cupular mechanics and extracellular receptor potentials were recorded to determine hair cell frequency selectivity. Results were obtained from two teleost fish species, the ruffe (Acerina cernua L.), a European temperate zone freshwater fish, and the tropical African knife fish (Xenomiystus nigri). In both species cupular displacement grows with increasing frequency of canal fluid displacement, reaching a maximum at 115 Hz in the ruffe and at 460 Hz in the African knife fish. Cupular best frequencies were independent of temperature. Cut-off frequencies of hair cell frequency selectivity were found to depend on temperature with a Q10 of 1.75, ranging from 116 Hz (4 degrees C) to 290 Hz (20 degrees C), as established in the ruffe. At normal habitat temperatures of the two fish species (ruffe, 4 degrees C; African knife fish, 28 degrees C), this results in hair cell cut-off frequencies that match the two different cupular best frequencies remarkably well. This match suggests adjusted signal transfer in these two peripheral stages of canal lateral line transduction.     

Physical dimensions influence the functional property of the semicircular canal

The functional dependence of the semicircular canal upon its physical dimensions was evaluated by measuring the internal radius (r), the radius of curvature (R) and the cupula radius (rC) of the posterior canal in 10 freshly dissected frog labyrinths. These values have been compared to the same parameters of the cat labyrinth. The coefficients I, B, K in the Steinhausen equation were determined for both animals. The A ratio between cupula deflection and endolymph displacement was also calculated by utilizing the Bernard equation. The A ratio is three times larger in the frog than in the cat. It follows that if the same acceleration produces similar endolymph displacements in the posterior canal of both animals, the cupula deflection will be larger in the frog. The solution of the Steinhausen equation in the presence of a constant acceleration, however, reveals that the same stimulus intensity will result in a larger endolymph displacement in the cat posterior canal; similarly, the endolymph displacement directly depends on the duration of the stimulating period in both animals. Contrary to the Bernard assumption, these effects generate a G ratio (psi frog/psi cat) which is less than the Q ratio (A frog/A cat). Moreover, G decreases on increasing the duration of the stimulating period. For stimuli of short duration the semicircular canal of a small animal is expected to exhibit a higher sensitivity than that of a larger one. However, the definitive primary afferent discharge will be largely controlled by the receptor/generator potential properties.     

Perspectives for the comprehensive examination of semicircular canal and otolith function.

A review is presented on the three-dimensional aspects of the vestibulo-oculomotor system and the current functional tests for unilateral examination of the individual receptors in the vestibular labyrinth. In the presentation, attention is directed towards the recently developed vestibular tests, which promise a more comprehensive examination of labyrinth function. More explicitly, unilateral tests for the utricle, saccule and the individual semicircular canals are discussed. Caloric irrigation and rotatory testing are widely used as tests for the integrity of the (horizontal) semicircular canals. Little useful diagnosis is made however on the vertical canals, not to mention the otolith organs. A promising approach to the examination of individual semicircular canal function has been described. This involves the perception of self-rotation in each of the planes of the semicircular canals. The patient/subject is rotated by an arbitrary amount on a standard Barany chair and then required to return the chair to its original position, by joystick control of the chair velocity. In order to test the vertical canals, the head of the subject/patient is positioned so that the plane of each canal lies in the plane of rotation. A promising unilateral test of saccular function involves the use of vestibular evoked myogenic potentials. Here it has been demonstrated that the saccules can be activated using brief, high-intensity acoustic clicks. The myogenic potential is measured using surface electrodes over the sternocleidomastoid muscles. Initial data from patients has indicated that the test is specific for unilateral saccule disorders. The unilateral test of utricle function is based on the eccentric displacement profile. Thus, eccentric displacement of the head to 3.5 cm during constant velocity rotation about the earth-vertical axis generates an adequate unilateral stimulation of the otolith organ, without involving the semicircular canals. This paradigm has also proved efficient in localizing peripheral otolith dysfunction by means of SVV estimation. This represents a novel test of otolith function that can be easily integrated into routine clinical testing. In contrast to the otolith-ocular response, the subjective visual vertical also reflects the processing of otolithic information in the higher brain centres (thalamus, vestibular cortex). Exploitation of the two complementary approaches therefore provides useful information for both experimental and clinical scientists. Of direct interest is the finding that testing with the subject rotating on-centre is sufficient to localize peripheral otolith dysfunction by means of SVV estimation. This represents a novel test of otolith function that can be easily integrated into routine clinical testing. In addition to caloric testing, which has remained the classical unilateral test of vestibular function, the newly developed tests should improve the differential diagnosis of vestibular disorders.     

Morphological aspects of potassium flow in the semicircular canal ampulla of the pigeon

Potassium ions are a prerequisite for the development and regulation of sensory cell stimulation in the inner ear. From the potassium-rich endolymph the ions flow into the sensory cells apically and are released basolaterally. After transport pathways of various lengths potassium is released again into the endolymph - in the cochlea by marginal cells of the stria vascularis, in the vestibular labyrinth by dark cells. While this long recycling pathway is relatively well-known in the cochlea, few studies have been conducted on the semicircular canal ampullae (SCCA) where its morphological basis is largely unknown. According to the present electron microscopic findings, potassium ions are initially released into the extracellular space during stimulation of the sensory cells and then absorbed by supporting and light cells. Finally they are transported transcellularly over numerous very long gap junctions into the region of the dark cells. From here they move to an extracellular compartment, which is more or less completely sealed off basally by basal plates of the light cells. Apically the intercellular space between light and dark cells is sealed by junctional complexes. This newly identified space in the SCCA corresponds to the extracellular compartment between the marginal and intermediate cells in the stria vascularis. At both sites, the cochlea and the SCCA, this probably serves as a regulatory valve, reservoir or storage space, particularly for potassium ions. It is likely that the different morphology of the ion transport pathways is related to the different flow levels of potassium ions expressed by the different levels of the so-called endocochlear potential and concomitant movement of other ions in the cochlea and SCCA.     

Brief communication: Investigation of the semicircular canal variation in the Krapina Neandertals

Previous studies comparing bony labyrinth morphology in geographically‐dispersed samples of Neandertals and modern Homo sapiens (H. sapiens) showed that Neandertals generally have smaller semicircular canals than modern H. sapiens (Hublin et al., 1996 ; Spoor et al., 2003 ; Glantz et al., 2008 ). Here we analyze the morphology of a single group of Neandertal specimens from one locale, the Krapina site, to determine the intraspecific variation in Neandertal semicircular canal sizes. Dimensions of the semicircular canals were collected from computed tomography scans of nine temporal bones. With the rare exception, the dimensions of the semicircular canals in the Krapina sample are similar to those previously reported across a geographically‐dispersed sample of Neandertals, further supporting previous studies that suggest low levels of variation in the semicircular canals for Neandertals. Am J Phys Anthropol 154:302–306, 2014. © 2014 Wiley Periodicals, Inc.     

Numerical modeling of the formation of steady-state nonequilibrium distributions of particles interacting through a power-law potential

The formation of a steady-state nonequilibrium distribution function of particles interacting through the repulsive potential U ~ α/r ^β(1≤β≤4), which operates at an infinite range, is studied numerically. The collisional particle dynamics in such a system is investigated using a spatially homogeneous nonlinear collision integral in the Landau-Fokker-Planck form, which is a model Boltzmann collision integral for arbitrary potentials of interaction accompanied by little momentum transfer between particles in collisions. Numerical modeling is based on completely conservative difference schemes. It is shown that the principal condition for the existence of steady-state nonequilibrium distributions is the presence of a particle or an energy flux oriented in the proper manner in momentum space. A steady-state local distribution exists inside the momentum interval between the energy source and sink and has the form of a gradually decreasing function. Since a radical change in the distribution function under nonequilibrium conditions leads to an anomalous enhancement of the conduction of a medium and its emission characteristics, the results obtained can be used, e.g., to predict the behavior of semiconductors with an intrinsic or extrinsic conductivity under the action of particle fluxes or electromagnetic radiation.     

Pre- and post-synaptic activity of glutamate on preparations of the frog semicircular canal

Glutamate (Glu) has at least two sites of action in the frog semicircular canal: the hair cell (presynaptic) and the primary afferent nerve fibres (postsynaptic). Glu's action on the hair cell results in an increased release of the natural transmitter which is responsible for a substantial increase in the frequency of firing in primary afferents. Glu produces a long-lasting depolarization in the afferent nerve fibres which does not by itself elicit any afferent discharge of impulses when the release of the natural transmitter is prevented. The difficulty of reconciling some of the observations made of the effects of Glu in semicircular canals with its presumed role as an afferent transmitter in this organ is discussed.     

Adenylate cyclase and carbonic anhydrase in the semicircular canal epithelium of the frog Rana esculenta

Summary Because the secretion of endolymph has been localized in the ampullar part of the frog semicircular canal, we attempted to determine by cytochemical methods the ultrastructural localization of two enzymes that are assumed to play a role in endolymph secretion: carbonic anhydrase and adenylate cyclase. Functionally, the epithelium of the frog semicircular canal can be schematically divided into three areas: sensory (crista ampullaris), secretory (dark cells), and non-sensory and nonsecretory (transitional and undifferentiated cells) areas. Carbonic anhydrase activity was widely distributed in dark cells. Dark cell labeling disappeared in the presence of acetazolamide. The other cells of the canal did not show any carbonic anhydrase labeling except for the supporting cells of the sensory cells. Adenylate cyclase activity was found on the basolateral and apical membranes of dark cells, and on the apical membrane of sensory cells; weak labeling was also observed in the other epithelial cells. In the apical membrane of the dark cells, adenylate cyclase labeling was dependent on the presence of vasotocin, the frog antidiuretic hormone. The dark cells of the frog semicircular canal thus possess the enzyme equipment needed for the secretion of endolymph and its possible hormonal regulation.     

Otolith and semicircular canal inputs to single vestibular neurons in cats.

Researchers studied the convergence of the vertical posterior semicircular canal (PC), saccular nerves (SAC), utricular nerves (UT), and horizontal semicircular canal nerves (HC) on single vestibular neurons. The vestibular neurons were categorized by their innervating targets. Vestibular neurons were classified as vestibulospinal proper neurons (VS), vestibulo-ocular proper neurons (VO), vestibulo-oculo-spinal neurons sending axon collaterals to the extraocular motoneuron pools and spinal cord (VOS), and vestibular nucleus neurons without axons to the oculomotor nuclei or the spinal cord (V). Results indicate that the percentage of convergence of VS neurons was higher that that of neurons sending axons to the oculomotor nuclei (VO and VOS). They conclude that the convergence of canal and otolith inputs likely contributes mainly to vestibulospinal reflexes by sending inputs to the neck and other muscles during head inclination, which creates the combined stimuli of angular and linear acceleration.