Supporting Evidence from Single Unit Experiments for the Cochlea as an Addressed Delay Line

WE have already outlined the principles of a theory of cochlear organization^{1, 2} whereby acoustic signal components in the low and mid frequency range—-that is to say, frequencies for which good or moderate phase locking of unit response is possible—are detected by the cochlea using an approximate cross-correlation mechanism which operates on the time varying signal displayed along the basilar membrane, the latter acting as an acoustic exponential delay line. The running correlations are performed using fixed patterns of control fibres addressed to the outer hair cells, the pattern of addressing for each control fibre group corresponding to an instantaneous wave pattern for a specific frequency defined by the location of the fibre system along the length of the membrane. The fibres of each control system synapse with the afferent dendrites associated with a definite inner hair cell and act as a frequency sensitive gate, the inner hair cell of the assembly providing generator current related to signal amplitude.     

The role of a reaction-diffusion system in the formation of hair fibres

Epithelial cells destined to form the hair fibre begin to differentiate while still in the hair follicle bulb. The fibre cells continue to differentiate as they migrate out of the bulb and up the follicle towards the skin surface. The anatomy of the hair follicle and the different cell types observed within the follicle are briefly reviewed. A theoretical scheme for cell differentiation, capable of producing all the observed mature cell types, is presented. A major component of the scheme is a reaction-diffusion system of morphogens similar to that originally proposed by Turing (1952). The mathematical solution of the equations defining the reaction-diffusion system within the follicle bulb is discussed. The sequence of patterns in the spatial distribution of the morphogens expected in the hair follicle bulb is calculated and found to be in good agreement with the sequence of patterns of orthocortical and paracortical cells in the fibre cross section as the diameter of the fibre increases. The spatial patterns of the morphogens are also compared with the shape of the fibre cross section. It is concluded that a reaction-diffusion system may play a major role in the morphogenesis of hair fibres.     

A comparative microphotometric study of succinate dehydrogenase activity levels in type I,IIA and IIB fibres of mammalian and human muscles

Summary Activity levels of succinate dehydrogenase (SDH) were determined kinetically by means of comparative microphotometric measurements in situ. Activities were correlated with fibre types classified histochemically according to Brooke and Kaiser (1970). Analyses of tibialis anterior muscles in the mouse, rat, guinea pig, rabbit, cat and the human showed pronounced variations in the activity profiles of type I, type IIA and IIB fibres of these muscles. Large scattering of enzyme activity existed in the three fibre populations. Overlaps of varying extent were found for the SDH profiles between the different muscles. Type I fibres reveal species diffeences in aerobic oxidative capacity. Whereas the majority of the IIB fibres in rabbit muscle tended to be low in SDH activity, the main fraction of this fibre population was characterized by high activities in mouse muscle. Similarly, the IIA fibre populations revealed opposite properties in mouse and rabbit muscles. These extremes as well as intermediate activity patterns indicate that no general scheme exists according to which the histochemically assessable myosin ATPase is correlated with the aerobic oxidative capacity of muscle fibres in various mammalian muscles.     

Scanning Microfocus Small Angle X-ray Scattering Study of the Avian Eggshell

Synchrotron microfocus small angle X-ray scattering was used to investigate the nanostructure and microscopic variation of eggshells. It uses a microbeam allowing the ability to probe interactions between the organic and inorganic components at nanometer level and is ideal for mapping over small areas to obtain a detailed analysis of structural variations. Thin sections of eggshells were scanned from the shell membrane （inner） to the cuticle （outer） surface. The data collected was used to produce two-dimensional maps showing microscopic changes within the different layers of the eggshell. The structural alterations ap- parently could have implications at the macroscopic level of the resulting eggshell. As the organic matrix is embedded within the eggshell this may contribute to the variations observed in calcite crystal form and texture, Structural information obtained about a biomaterial at different length scales is important in relating the structure to its functional properties. This knowledge and the principles behind the formation of biomaterials could be used in the attempt of bioengineering new systems.     

A synchrotron radiation X-ray diffraction study of the crystallinity of tendon fibres

The equatorial diffraction pattern of tendon collagen fibres was measured during short successive exposures at different lengths using a double focusing X-ray synchrotron radiation camera with film and with an area detector. Similarly, patterns from thin fibres from premature rats were recorded. The patterns unambiguously illustrate the relationship between fibre crystallinity and the age of the animal. Further, the results indicate that in the initial part of the linear region of the stiffness-versus-length curve, the collagen fibres are characterized by a quasihexagonal arrangement of collagen molecules, whereas at the end of this region, the molecular arrangement becomes hexagonal.     

Formation of a unique crystal morphology for the poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behaviors of the poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymer with the PEG weight fraction of 0.50 (PEG(50)-PCL(50)) was studied by DSC, WAXD, SAXS, and FTIR. A superposed melting point at 58.5 degrees C and a superposed crystallization temperature at 35.4 degrees C were obtained from the DSC profiles running at 10 degrees C/min, whereas the temperature-dependent FTIR measurements during cooling from the melt at 0.2 degrees C/min showed that the PCL crystals formed starting at 48 degrees C while the PEG crystals started at 45 degrees C. The PEG and PCL blocks of the copolymer crystallized separately and formed alternating lamella regions according to the WAXD and SAXS results. The crystal growth of the diblock copolymer was observed by polarized optical microscope (POM). An interesting morphology of the concentric spherulites developed through a unique crystallization behavior. The concentric spherulites were analyzed by in situ microbeam FTIR, and it was determined that the morphologies of the inner and outer portions were mainly determined by the PCL and PEG spherulites, respectively. However, the compositions of the inner and outer portions were equal in the analysis by microbeam FTIR.     

Structure,composition and mechanical properties of the silk fibres of the egg case of the Joro spider, <Emphasis Type="Italic">Nephila clavata</Emphasis> (Araneae,Nephilidae)

The silk egg case and orb web of spiders are elaborate structures that are assembled from a number of components. We analysed the structure, the amino acid and fibre compositions, and the tensile properties of the silk fibres of the egg case of Nephila clavata. SEM shows that the outer and inner covers of the egg case consist of thick, medium and thin silk fibres. The silk fibres of the outer cover of the egg case are probably produced by the major and minor ampullate glands. The silk fibres of the inner cover of the egg case from cylindrical glands appears to be distinct from the silk fibres of the major ampullate glands based on their micro-morphology, mole percent amino acid composition and types, and tensile behaviour and properties. Collectively, our investigations show that N. clavata uses silk fibres from relatively few glands in varying combinations to achieve different physical and chemical properties (e.g., color, diameter, morphology and amino acid composition) and functional and mechanical properties in the different layers of the egg case.     

Lipoprotein charge and vascular lipid metabolism

The internal lipids were extracted from untreated hair without surface lipids. Liposomes were formed with the internal lipids at different hydration levels to determine the organization of these lipids and the influence of the water content on the lamellar structure of the hair fibres by X-ray Scattering (SAXS). Two structures of hair lipids were observed at 4.5 and approximately 9.0nm with a different behaviour as a function of water content: the largest bilayer being the one that showed a capacity to retain water inside its structure. SAXS was also applied directly to three samples: a packed swatch of hair fibres at 60% RH, fibres soaked in water and delipidized fibres. Only the lamella at 9.0nm was slightly affected by water content. Moreover, there was a small diminution in intensity probably due to a high permeability of wet fibres which could give rise to a disorder of the lipid structure. These two lamellar rearrangements are probably made up of lipids with a different and specific hydrophilic/hydrophobic balance.     

Nitric oxide synthase in human skeletal muscles related to defined fibre types

Skeletal muscle functions regulated by NO are now firmly established. However, the knowledge about the NO synthase (NOS) expression related to a defined fibre type in human skeletal muscles necessitates further clarification. To address this issue, we examined localization of NOS isoforms I, II and III, in human skeletal muscles employing immunocytochemical labeling with tyramide signal amplification complemented with enzyme histochemistry and Western blotting. The NOS immunoreactivity was related to fibre types of different classification systems: physiological classification into slow and fast, ATPase classification into I, IIA, IIAX, IIX, and physiological-metabolic classification into slow-oxidative (SO), fast-oxidative glycolytic (FOG) and fast-glycolytic (FG). We found a correlation of NOS I–III immunoreactivity to metabolic defined fibre types with strong expression in FOG fibres. This implies that NO as modulator of muscle function is involved in oxidative metabolism in connection with fast force development, which only occurs in FOG fibres. The NOS expression showed no correlation to ATPase fibre subtypes due to the metabolic heterogeneity of ATPase fibre types. Healthy and affected vastus medialis muscles after anterior cruciate ligament rupture revealed similar NOS expression level as shown by Western blotting with, however, different expression patterns related to the fibre types in affected muscles. This suggests an altered modulation of force development in the fibres of diseased muscles.     

The influence of humidity on the viscoelastic behaviour of human hair

The possibility of curling hair is attributed to the fact that the mechanical properties of hair fibres depend on time, temperature and humidity. In this study the dependence of the viscoelastic behaviour of human hair fibres on humidity is characterised in a bending deformation. An experimental set-up was used to perform bending relaxation measurements at different humidities. The relaxation data were fitted using a so-called "stretched exponential equation". The humidity dependence was incorporated by applying time-humidity superposition. Also, the influence of humidity on the initial E-modulus was found. The influence of humidity on the behaviour of human hair fibres could be modelled by using a general characterisation of the behaviour of human hair fibres.The general characterisation is used to predict the recovery in a human hair fibre after curling. The predicted recovery appeared to agree reasonably well with experimentally determined values.     

Hair curvature: a natural dialectic and review

Although hair forms (straight, curly, wavy, etc.) are present in apparently infinite variations, each fibre can be reduced to a finite sequence of tandem segments of just three types: straight, bent/curly, or twisted. Hair forms can thus be regarded as resulting from genetic pathways that induce, reverse or modulate these basic curvature modes. However, physical interconversions between twists and curls demonstrate that strict one‐to‐one correspondences between them and their genetic causes do not exist. Current hair‐curvature theories do not distinguish between bending and twisting mechanisms. We here introduce a multiple papillary centres (MPC) model which is particularly suitable to explain twisting. The model combines previously known features of hair cross‐sectional morphology with partially/completely separated dermal papillae within single follicles, and requires such papillae to induce differential growth rates of hair cortical material in their immediate neighbourhoods. The MPC model can further help to explain other, poorly understood, aspects of hair growth and morphology. Separate bending and twisting mechanisms would be preferentially affected at the major or minor ellipsoidal sides of fibres, respectively, and together they exhaust the possibilities for influencing hair‐form phenotypes. As such they suggest dialectic for hair‐curvature development. We define a natural‐dialectic (ND) which could take advantage of speculative aspects of dialectic, but would verify its input data and results by experimental methods. We use this as a top‐down approach to first define routes by which hair bending or twisting may be brought about and then review evidence in support of such routes. In particular we consider the wingless (Wnt) and mammalian target of rapamycin (mTOR) pathways as paradigm pathways for molecular hair bending and twisting mechanisms, respectively. In addition to the Wnt canonical pathway, the Wnt/Ca²⁺ and planar cell polarity (PCP) pathways, and others, can explain many alternatives and specific variations of hair bending phenotypes. Mechanisms for hair papilla budding or its division by bisection or fission can explain MPC formation. Epithelial‐to‐mesenchymal (EMT) and mesenchymal‐to‐epithelial (MET) transitions, acting in collaboration with epithelial‐mesenchymal communications are also considered as mechanisms affecting hair growth and its bending and twisting. These may be treated as sub‐mechanisms of an overall development from neural‐crest stem cell (NCSC) lineages to differentiated hair follicle (HF) cell types, thus providing a unified framework for hair growth and development.     

Developmental changes in cell wall structure of phloem fibres of the bamboo Dendrocalamus asper

BACKGROUND AND AIMS: Bamboo culms have excellent physical and mechanical properties, which mainly depend on their fibre content and anatomical structure. One of the features which is known to contribute to the high tensile strength in bamboo is the multilayered structure of the fibre cell wall. The aim of this study was to characterize the development of the layered structure in fibre cell walls of developing and maturing culms of Dendrocalamus asper. METHODS: Cell wall development patterns were investigated in phloem fibre caps of vascular bundles in the inner culm wall areas of Dendrocalamus asper of three different age classes (<6 months old, 1 year old, 3 years old). A combination of light microscopy and image analysis techniques were employed to measure cell wall thickness and to determine number of cell wall layers, as well as to describe the layering structure of fibre walls. Two-dimensional maps showing the distribution pattern of fibres according to the number of cell wall layers were produced. KEY RESULTS: The cell walls of fibres in phloem fibre caps located in the inner part of the culm wall of D. asper developed rapidly during the first year of growth. Six different fibre types could be distinguished based upon their cell wall layering and all were already present in the young, 1-year-old culm. In the mature stage (3 years of age) the multilayering was independent of the cell wall thickness and even the thinner-walled fibres could have a large number of wall layers. The multilayered nature of cell wall structure varied considerably between individual cells and was not exclusively related to the cell wall thickness. Nevertheless, fibres at the periphery of the fibre bundles and immediately adjacent to the phloem elements exhibited a consistent and high degree of layering in their cell walls. CONCLUSIONS: The multilayered structure of fibre cell walls was formed mainly during the first year of growth by the deposition of new wall layers of variable thickness, resulting in a high degree of heterogeneity in the layering patterns amongst individual fibres. A degree of 'order' in the distribution of multilayered fibres within the caps does exist, however, with multilayered cell walls common in fibres adjacent to phloem elements and around the edge of the fibre cap. These findings confirm the observations, primarily in Phyllostachys viridi-glaucescens. The layering structure was not found to be specifically related to the thickness of the cell wall.     

Immunohistochemical analysis of the human psoas major muscle with regards to the body side and aging

The aim of our study was to explore the age related changes of the fibre type composition of the human psoas major muscle. Moreover, we wanted to compare the fibre type composition of the left and right muscle. Muscle samples were collected from 15 young and 15 old males. Type I, IIA and IIX muscle fibres were typed using myosin heavy chain identification. The serial transverse sections were analysed using a light microscope. Results of our study showed that the age-related atrophy affected all three fibre types. Type IIA fibres were affected most profoundly while type I fibres were affected most weakly. The percentage of the different fibre types did not change during aging. There were no differences in the fibre type composition between the left and right muscle. Human psoas major muscle undergoes normal aging changes with the atrophy of all three fibre types, whereas atrophy most profoundly affects type IIA fibres. No differences in the fibre type composition between the left and right muscle point to the equal engagement of both legs in normal everyday activities of human.     

Inter- and intraspecies comparisons of fibre type distribution and of succinate dehydrogenase activity in type I, IIA and IIB fibres of mammalian diaphragms

Fibre types in the costal region of the diaphragm muscle of several mammalian species with widely different respiratory rates were examined microphotometrically for succinate dehydrogenase (SDH) activity. Mean activities indicated no significant (p greater than 0.05) difference between the type I and IIA fibres for any of the species examined. SDH activities in type IIB fibres were significantly lower (p less than 0.05) than either the type I or type IIA fibres in the cat, guinea pig, rat and rabbit whereas in the mouse no difference was found. The dog had no classical type 1B fibres. Analysis of the distribution of SDH activities by fibre type indicated a wide scattering of scores with no distinct separation between fibre types. Large differences in SDH activity were noted between species. Mean SDH activities were highest in the mouse and rat, intermediate in the rabbit and guinea pig and lowest in the cat and dog. These data suggest an association between respiratory rate and aerobic oxidative potential of the various fibre types in diaphragms of the species examined.     

Investigation of human hair cuticle structure by microdiffraction: direct observation of cell membrane complex swelling.

The cuticle of mammalian hair fibres protects the core of the fibre against physical and chemical stress. The structure and some of the properties of the cuticle have been extensively studied by electron microscopy. However, there is still a need for a less invasive structural probe. For this purpose, microdiffraction experiments have been carried out on human hair samples showing a characteristic small-angle X-ray scattering pattern for the cuticle. This pattern has been assigned to the cell membrane complex (CMC) between each cuticle scale. Using a simple model of the electron density within the CMC, values have been derived for the average thickness of the beta- and delta-layers which are close to those obtained by electron microscopy. In order to illustrate the potentialities of microdiffraction in studying the properties of the cuticle, the effect of water sorption has been monitored. Using the intensity modelling described above, a 10% swelling of the delta-layer's thickness has been observed. This study shows that structural modifications of the CMC by physical or chemical stress can be followed directly on the cuticle of human hair fibres by microdiffraction analysis.     

Inter- and intraspecies comparisons of fibre type distribution and of succinate dehydrogenase activity in type I,IIA and IIB fibres of mammalian diaphragms

Summary Fibre types in the costal region of the diaphragm muscle of several mammalian species with widely different respiratory rates were examined microphotometrically for succinate dehydrogenase (SDH) activity. Mean activities indicated no significant (p>0.05) difference between the type I and IIA fibres for any of the species examined. SDH activities in type IIB fibres were significantly lower (p<0.05) than either the type I or type IIA fibres in the cat, guinea pig, rat and rabbit whereas in the mouse no difference was found. The dog had no classical type 1B fibres. Analysis of the distribution of SDH activities by fibre type indicated a wide scattering of scores with no distinct separation between fibre types. Large differences in SDH activity were noted between species. Mean SDH activities were highest in the mouse and rat, intermediate in the rabbit and guinea pig and lowest in the cat and dog. These data suggest an association between respiratory rate and aerobic oxidative potential of the various fibre types in diaphragms of the species examined.     

STRUCTURAL BIOLOGY OF THE FIBRES OF THE COLLAGENOUS AND ELASTIC SYSTEMS

The different types of fibres of the collagenous and elastic systems can be demonstrated specifically in tissue sections by comparing the typical ultrastructural picture of each of the fibre types with studies using selective staining techniques for light microscopy. A practicalmodus operandi, which includes the recommended staining procedures and interpretation of the results, is presented. Micrographs and tables are provided to summarize the differential procedures. Reticulin fibres display a distinct argyrophilia when studied by means of silver impregnation techniques, and show up as a thin meshwork of weakly birefringent, greenish fibres when examined with the aid of the Picrosirius-polarization method. In addition, electron-microscopic studies showed that reticulin fibres are composed of a small number of thin collagen fibrils, contrasting with the very many thicker fibrils that could be localized ultrastructurally to the sites where non-argyrophilic, coarse collagen fibres had been characterized by the histochemical methods used. The three different fibre types of the elastic system belong to a continuous series: oxytalan—elaunin—elastic (all of the fibre types comprising collections of microfibrils with, in the given sequence, increasing amounts of elastin). The three distinct types of elastic system fibres have different staining characteristics and ultrastructural patterns. Ultrastructurally, a characteristic elastic fibre consists of two morphologically different components: a centrally located solid cylinder of amorphous and homogeneous elastin surrounded by tubular microfibrils. An oxytalan fibre is composed of a bundle of microfibrils, identical to the elastic fibre microfibrils, without amorphous material. In elaunin fibres, dispersed amorphous material (elastin) is intermingled among the microfibrils.     

Collagen and mature elastic fibre organisation as a function of depth in the human cornea and limbus

A network of circumferentially oriented collagen fibrils exists in the periphery of the human cornea, and is thought to be pivotal in maintaining corneal biomechanical stability and curvature. However, it is unknown whether or not this key structural arrangement predominates throughout the entire corneal thickness or exists as a discrete feature at a particular tissue depth; or if it incorporates any elastic fibres and how, with respect to tissue depth, the circumcorneal annulus integrates with the orthogonally arranged collagen of the central cornea. To address these issues we performed a three-dimensional investigation of fibrous collagen and elastin architecture in the peripheral and central human cornea using synchrotron X-ray scattering and non-linear microscopy. This showed that the network of collagen fibrils circumscribing the human cornea is located in the posterior one-third of the tissue and is interlaced with significant numbers of mature elastic fibres which mirror the alignment of the collagen. The orthogonal arrangement of collagen in the central cornea is also mainly restricted to the posterior stromal layers. This information will aid the development of corneal biomechanical models aimed at explaining how normal corneal curvature is sustained and further predicting the outcome of surgical procedures.     

Some implications of helical fibres in worm cuticles

The cuticles of many worms contain a cylindrical trellis made of layers of collagen fibres wound round the body in left- and right-hand helices. This kind of extensible skeletal structure imposes various constraints on a worm's behaviour, and some of these are examined, using the nematomorph Parachordodes woltersforffii as the main example. Upon extension or shortening of the cuticle, neighbouring fibres in one layer will eventually touch and so limit further movement; this in turn affects the extent of shortening, elongation, bending and coiling of the whole worm. Simple equations relate: the angle between a fibre and the worm's long axis; fibre spacing and radius; worm body radius and radius of curvature. The relevance to the life of the worm of fibre arrangement, matrix properties and volume changes is discussed.