The ultrastructure of the round window membrane of the cat

The ultrastructure of the round window membrane of the cat was investigated. Three distinct layers were recognised and described. It was established that the outer epithelial layer is non-ciliated, but often contains microvilli. The middle layer, under the basement membrane, contains a large amount of collagen and elastic fibres in addition to fibrocytes. The inner layer is a continuation of the epithelial layer of the perilymphatic space. The thickness of the membrane has been measured as being 15--20 micrometer. The latest human audiological and clinical observations concerning the function and rupture of the round window membrane emhasise the importance of the electron microscopic study of this membrane.     

豚鼠变应性鼻炎模型鼻黏膜基底膜增厚重塑的超微结构

目的 观察豚鼠变应性鼻炎模型鼻黏膜上皮下基底膜增厚重塑超微结构的病理变化。方法 用橄榄油将甲苯-2，4-二异氰酸酯配成浓度为10％溶液作为致敏剂，滴鼻，建立豚鼠变应性鼻炎动物模型8例。另取8例正常豚鼠作对照。致敏结束、模型成功后，取两组鼻黏膜进行透射电镜观察。结果 透射电镜见基底膜分透明板、致密板和网板三层，变应性鼻炎在网板出现胶原纤维沉积、增厚，无细胞成分。透明板、致密板无变化。结论 变应性炎症可引起鼻黏膜上皮下胶原纤维沉积，引起基底膜增厚重塑。     

The three-dimensional fibrillar arrangement of the basilar membrane in the mouse cochlea

The three-dimensional fibrillar arrangement of the basilar membrane in the mouse cochlea was studied using scanning electron microscopy. Fibrils of the basilar membrane were exposed by removing cellular elements of the cochlea using a sodium hydroxide maceration technique. The arrangement of fibrils in the basilar membrane was different between the pars arcuata and pars pectinata. In the pars arcuata, fibrils were arranged in radial and spiral direction, showing a woven pattern. In the pars pectinata, most of the fibrils ran in the radial direction. These findings suggest that the vibration pattern of the pars arcuata and pars pectinata is different when the basilar membrane vibrates.     

Mechanics of the basilar membrane in Caiman crocodilus

Vibration measurements were made at a number of positions near the proximal (basal) end of the basilar membrane, and on the columella footplate, of Caiman crocodilus using a capacitive probe. The measurements established the existence of a mechanical travelling wave in this species. They showed no significant change of mechanical tuning with temperature, and were highly significantly different from previous reports of neural temperature sensitivity (Smolders, J. and Klinke, R. (1984): J. Comp. Physiol. 155, 19-30). Thus the neural sensitivity to temperature change appears not to depend upon basilar membrane mechanics. One interpretation of this is that the basilar membrane passively precedes an active temperature-sensitive filter. It was also found that the limbus supporting the basilar membrane had a measurable, but unturned, vibration and that the effect of draining scala tympani for the measurements was to increase the basilar membrane tuning frequency by a factor of about 1.5.     

The presence and arrangement of type II collagen in the basilar membrane

Previous studies demonstrating the presence of collagen II in the basilar membrane have used a biochemical approach or have used immunohistochemistry at the light microscopic level. In this investigation both the presence and arrangement of collagen II were demonstrated at the ultrastructural level using pre- and post-embedding immunoelectron microscopy. Labeling was dependent on the development of protocols to expose epitopes while maintaining identifiable ultrastructure. Both positive and negative controls indicate that the labeling was specific for collagen II. Collagen II was detected in the fibrous sheet of the pars tecta and in the two fibrous layers of the pars pectinata. It was detected in situ and on isolated individual 10-12 nm fibrils. The presence of collagen II in all the fibrous layers of the basilar membrane places constraints on the biomechanical properties of this important structure.     

Damage of the basilar membrane by acoustic stimulation

Summary Sound exposures of more than 130 dB lead to typical tears in the basilar membrane in the area of maximal damage. The position, size, and number of these tears are evaluated.     

Travelling wave motion along the pigeon basilar membrane

The basilar membrane (BM) motion in the pigeon was measured using the M?ssbauer technique. Tonotopic frequency mapping and travelling wave motion were observed over the basal 35% of the BM. The sensitivity and sharpness of the BM tuning depended on the physiological condition of the cochlea. The observed amplitude responses did not match the frequency threshold tuning curves of single primary auditory fibers.     

Homodyne interferometer for basilar membrane measurements

Techniques available for measuring the mechanical response of the inner ear are compared. These include capacitive probe, M?ssbauer and interferometric methods. The theory of a homodyne interferometer utilized for inner ear measurements is given. Experimental apparatus built to test the interferometer performance is described. Experimental results show that the measuring system can detect vibrations as low as 3 X 10(-12) cm. Its frequency response is flat within 1 dB from 0.1 to 40 kHz. It has a linear dynamic range of over 90 dB. Immunity of the interferometer to various disturbances is demonstrated.     

State of stress within the basilar membrane: a re-evaluation of the membrane misnomer

By deforming and making incisions in the basilar membrane (BM), von Békésy showed that the BM seems to behave as a thin elastic plate, rather than as a membrane. However, it has never been shown whether a traveling wave could be sustained by a prestretched material in which the tension is insufficient to cause a visible retraction of the cut edges of an incision when viewed with a light microscope. We have shown that the necessary radial tension would decrease exponentially along the cochlea, from a value of 39 ± 9 N/m at the base, with a space constant of 4.3 ± 1.1 mm, for the guinea pig. This variable tension would be produced by a constant prestretching surface force of 2.4 ± 0.1 × 10⁶ N/m², acting on the BM edges. Using values of Young's modulus in the radial direction, ranging from that of elastin to collagen, it is shown that this force would most likely cause a visible retraction of the cut edges of an incision. Therefore one must either conclude, once again, that the BM is effectively an unstretched material or question the original interpretation of the incision experiments.     

Point-impedance characterization of the basilar membrane in a three-dimensional cochlea model

In this paper we derive which impedance definition appropriately represents the basilar membrane in a simple three-dimensional model (de Boer's 'block model') of the cochlea. The starting point of our considerations is a system of parallel visco-elastic beams as characterization of the basilar membrane. It is possible to transform this representation into an impedance concept by observing that the membrane velocity is to a very good approximation distributed over the width as a centred half cosine function, independent of the pressure distribution. The ensuing impedance definition is more accurate than the one proposed by de Boer (Hearing Res. 4, 53-77, 1981). The improvement to the model solutions is moderate, however, as appears from numerical calculations of the basilar membrane velocity.     

Studies on fibrous tissues of the basilar membrane in inner ear

Of a number of electron microscope studies on the basilar membrane of the inner ear cochlear duct so far reported, none seems to have been conducted using PAM of R.R. staining, excellent stainings especially suited for the observation of connective tissue. In this study the basilar membrane of the cochlear duct in young and mature guinea pigs and human fetuses was examined with an electron microscope using these stainings, and obtained the interesting results described below. Fibrils of the basilar membrane, although strongly PAM-positive, all lacked periodic stripes, indicating that they were collagenous fibrils in an immature state. Young guinea pigs clearly differed from mature ones in that numerous fibroblasts were present. In human fetuses, the basilar membrane exhibited no clear fibrillar structure in the 13th week, but had PAM-positive fibrils in the 20th week. By the 23rd week, it had assumed roughly the same structure as in adults, although numerous fibroblasts were still present, and resembled the basilar membrane in young guinea pigs. The basilar membrane is a part of a unique organ, a sensory organ. Though comparison is difficult because of the extremely complicated anatomy of the organ, it is concluded that the fibrils of basilar membrane are collagenous fibrils in a peculiarly immature state, and similar to those in the cartilage and tympanic membrane.     

Morphometric analysis of age-related changes in the human basilar membrane.

The histopathologic correlates of presbycusis suggest several categories, including degeneration of sensory cells, neurons, or the stria vascularis. Lack of clear-cut histopathologic changes in some cases has suggested an "indeterminate category"; however, several studies have suggested that a disorder of the basilar membrane (BM) may underlie indeterminate presbycusis. The objective of the present study was to quantify age-related changes in the human BM and correlate them with audiometric patterns. Under high-resolution light microscopy, BM thickness was calculated, and the number of tympanic mesothelial cells (TMCs) lining the BM was counted, at 4 cochlear locations in 92 temporal bones. The control group (n = 80) included subjects from 10 decades of age with normal hearing and/or histopathologic findings. The indeterminate group (n = 12) consisted of elderly patients (ages 64 to 91 years) with hearing loss and no apparent histopathologic changes. Age-related BM thickening was seen in both groups, but only in the most basal cochlear region. The BM thickness in the indeterminate group was not significantly different from that of age-matched controls. Counts of TMCs showed age-related decreases in all cochlear regions in both groups; however, TMC counts in the indeterminate group were not different from those of age-matched controls. The results suggest that BM histopathology is not a common cause of presbycusis. Although age-related BM thickening, seen in both groups, could contribute to hearing loss, the extreme basal region, to which the thickening was confined, is not tested in routine audiometry.     

Auditory brainstem correlates of basilar membrane nonlinearity in humans

A behavioral measure of the basilar membrane response can be obtained by comparing the growth in forward masking for maskers at, and well below, the signal frequency. Since the off-frequency masker is assumed to be processed linearly at the signal place, the difference in masking growth with level is thought to reflect the compressive response to the on-frequency masker. The present experiment used an electrophysiological analog of this technique, based on measurements of the latency of wave V of the auditory brainstem response elicited by a 4-kHz, 4-ms pure tone, presented at 65 dB SPL. Responses were obtained in quiet and in the presence of either an on-frequency (4 kHz) or an off-frequency (1.8 kHz) pure-tone forward masker. Wave V latency increased with masker level, although the increase was greater for the off-frequency masker than for the on-frequency masker, consistent with a more compressive response to the latter. Response functions generated from the data showed the characteristic shape, with a nearly linear response at lower levels and 4:1 compression at higher levels. However, the breakpoint between the linear region and the compressive region was at about 60 dB SPL, higher than expected on the basis of previous physiological and psychophysical measures.     

Risk of basilar membrane perforation by intracochlear electrodes

Insertion of intracochlear electrodes may damage the basilar membrane, the stria vascularis and adjacent structures. When electrodes were placed in human temporal bone specimens, perforations were shown to be independent of the type of implant used, the depth of insertion or the use of a lubricating agent. Helical electrode reinforcements and failure to enlarge the round window frame increase the risk of damage. Perforations are invariably localized at a distance of about 7-14 mm from the round window and occur at the site where the curvature of the basal turn is greatest.     

Laser Doppler velocimetry of basilar membrane vibration.

A method is described for the measurement of basilar membrane (BM) vibration velocimeter (LDV). The instrumentation was coupled to a compound microscope which served to visualize reflective glass microbeads placed on the BM. The laser beam of the LDV was focused in the microscope object plane and positioned over the reflective bead. We show examples of frequency tuning curves and displacement input/output intensity functions obtained with the technique.