Dendrites of cockroach tibial spine mechanoreceptors contain hundreds of free microtubules, which may have some relation to the generation of electrical activity. Deflection of a spine produces a train of action potentials. Continuous perfusion over a period of 4 hours results in no response decrement. Perfusion with 10mM colchicine reversibly inhibits the response within 5-7 minutes. Irreversible inhibition is produced by perfusion with 1mM vinblastine sulfate in perfusion solution containing 1% dimethyl sulfoxide. Deuterium oxide does not inhibit at concentrations less than 50%, nor does it counteract inhibition by 10mM colchicine. Colchicine may be affecting (1) intracellular microtubules, (2) membraneous tubulin, (3) other membrane components, or (4) axoplasmic transport of essential materials to the sensory dendrites.

Mechanosensation, the ability for cells to sense and respond to physical cues, is a ubiquitous process among living organisms and its dysfunction can lead to devastating diseases, including atherosclerosis, osteoporosis, and cancer. The primary cilium is a solitary, immotile organelle that projects from the surface of virtually every cell in the human body and can function as a mechanosensor across diverse biological contexts, deflecting in response to fluid flow, pressure, touch and vibration. It can detect urinary flow rate in the kidney, monitor bile flow in the liver, and distinguish the direction of nodal flow in embryos. In this thesis, we examined the interplay of biology and mechanics in the context of this multifunctional sensory organelle from the tissue to subcellular scale. In the first part of this work, we examined the cilium at the tissue level. Primary cilia are just beginning to be appreciated in bone with studies recently reporting loss of cilia results in defects in skeletal development and adaptation. We disrupted primary cilia in osteocytes, the principal mechanosensing cells in bone, and demonstrated that loss of primary cilia in osteocytes impairs load-induced bone formation. Over the course of our work with primary cilia, we also identified the need for more standardized imaging approaches to the cilium and presented an improvement to distinguishing proteins within the cilium from the rest of the cell. In the later part of this work, we examined the primary cilium at the subcellular level. While deflection is integral to the cilium's mechanosensory function, it remains poorly understood and characterized. Using a novel experimental and computational approach to capture and determine the mechanical properties of the cilium, we demonstrated cilium deflection can be mechanically and chemically modulated. We revealed a mechanism, acetylation, through which this mechanosensor can adapt and regulate overall cellular mechanosensing. By modifying our combined experimental and computational approach, we analyzed cilium deflection in vivo for the first time. Collectively, this work uncovers new insights across biological scales in the primary cilium as an extracellular nexus integrating mechanical stimuli and cellular signaling. Understanding the mechanisms driving cilium mechanosensing has broad reaching implications and unlocks the cilium's potential as a therapeutic target to treat impaired cellular mechanosensing critical to a multitude of diseases.

Animal experiments indicate that the main form of feedback for jaw-closing muscles is from periodontal mechanoreceptors (PMRs). However, due primarily to limitations on methods, this is yet to be confirmed in humans. The main aim of this thesis was to investigate the reflex contribution of PMRs to the human jaws using vertical (axial) stimulation. To this end the electromyographic and bite force responses of the jaw to a number of different mechanical stimulus conditions, delivered to both the upper central incisors and the upper right first molars, were investigated. The principal hypothesis was that PMRs are responsible for the majority of the reflex responses seen in the human jaw muscles. Furthermore this reflex response is modulated by different characteristics of the stimulus such as: rate of rise, maximum force applied, the amount of constant offset force (preload), the level of muscle contraction and also the physical characteristics of the subject's jaw including: dental health and tooth spacing. These studies have contributed towards the understanding of the neuronal wiring and the receptor systems contained in the jaw. The results indicate that PMRs around the incisors are of fundamental importance for the development of reflex patterns but little if any PMR related reflexes exist around the molar teeth. The reflexes originating from the PMRs around the incisors are modulated by different mechanical characteristics of the stimulus, thus helping to explain how the jaw muscles perform numerous and complex patterns of activation which move the jaw in many different ways and develop forces that are optimum for the task at hand. / Thesis (Ph.D.)--School of Molecular & Biomedical Science, 2004.

published_or_final_version / Physiology / Master / Master of Philosophy

An occupational exposure to hand-arm vibration can cause a complex of neurological, vascular and musculo-skeletal disturbances, known as the 'vibration syndrome'. However, the underlying pathophysiological mechanisms are not at all clear. Early signs of an incipient vibration syndrome are often intermittent disturbances in the cutaneous sensibility of the fingers, i.e. numbness and/or tactile paresthesias. At later stages, a vasoconstrictive phenomenon appears, usually as episodes of finger blanching. When using a vibratory tool, all mechanical energy entering the body has to be transmitted through, or absorbed by, the glabrous skin in contact with the handle. Therefore, the aims of this study was to investigate: (i) mechanical responses of the skin to vibrations, (ii) the response properties of cutaneous mechanoreceptors to vibrations, and (iii) influences of vibration exposure on touch perception. It was found by measuring the mechanical point impedance (0.02-10 kHz) that the skin is easy to make vibrate within the range of 80 to 200 Hz. Within or close to this range are the dominant frequencies of many vibratory tools. Thus, strong mechanical loads, such as compressive and/or tensile strain, can appear in the skin which, in turn, may induce temporary or permanent injuries. Recordings of impulses in single mechanoreceptive afferents, while the skin as exposed to vibrations, were obtained using needle electrodes inserted into the median nerve. The 4 types of mechanoreceptive afferents (FA I, FA II, SA I, and SA II) in the glabrous skin exhibited different response characteristics to vibrations. The FA I units were most easily excited at vibratory frequencies between ca 8 and 64 Hz and the FA II units between ca 64 and 400 Hz. The SA units were most sensitive at lower frequencies. At high stimulus amplitudes, such as may occur while using vibratory tools, a considerable overlap existed between the frequency ranges at which the units were exited. Evidence was also provided, that mechanical skin stimuli produced by edges of a vibrating object, compared to flat surfaces, more vigorously excited the FA I and particularly the SA I units. Thus, a marked edge enhancement, essential for tactile gnosis and precision manipulation, seems to exist already within the peripheral nervous system. Acure impairment of tactile sensibility caused by vibrations, proved to be due to a reduced sensitivity of the mechanoreceptive afferents. A loss of manual dexterity a*vi an increased risk for accidents may therefore appear, both during and after a vibration exposure. Percussive tools, high speed drills and ultrasonic devices are known to generate mechanical energy at frequencies above 1 kHz, i.e. frequencies usually not felt. At these frequencies, it is known that most of the energy, entering the body, is absorbed by the skin. Therefore, it was investigated whether a long-term exposure to high-frequency vibration may have a detrimental effect on the cutaneous sensitivity. One group of dentists and one of therapists, professionally exposed to high-frequency vibrations, were studied with regard to vibrotactile thresholds in their hands. The study showed that deleterious effects on tactile sensibility, at local exposure to high frequency vibration, can not be excluded. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1985, härtill 6 uppsatser</p> / digitalisering@umu

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 4 uppsatser.

Thesis (M. Phil.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 79-98).

Made available in DSpace on 2014-06-11T19:30:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-06-22Bitstream added on 2014-06-13T18:40:45Z : No. of bitstreams: 1 henriques_vmc_dr_jabo.pdf: 21990041 bytes, checksum: 72a1d82d9783cfd7140b55f66e403d2d (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Os crustáceos dispõem de estruturas sensitivas que permitem receber estímulos do meio. Estes são usados para localizar e capturar o alimento. As estruturas de quimiorrecepção e mecanorrecepção são reconhecidas como os principais sentidos usados pelos crustáceos decápodas para identificação de partículas alimentares. O Macrobrachium rosenbergii é uma espécie que passa por uma fase planctônica e outra bentônica, faz grandes migrações a favor ou contra a corrente conforme a fase do ciclo de vida ou estágio fisiológico e muda o hábito alimentar de carnívoro à onívoro. Portanto, deve apresentar mecanismos de percepção dos estímulos do meio, que se modificam ao longo do desenvolvimento. Assim, a hipótese levantada nessa pesquisa foi que M. rosenbergii apresenta estruturas sensitivas na superfície do corpo e apêndices, que se modificam desde a eclosão da larva até a fase adulta. O objetivo deste trabalho foi pesquisar a ocorrência de estruturas sensitivas ao longo do desenvolvimento ontogenético de M. rosenbergii. A pesquisa ocorreu no setor de carcinicultura do CAUNESP. As larvas e pós-larvas foram coletadas de larvicultura sob sistema fechado dinâmico segundo Valenti (1998) e os juvenis e adultos dos sistemas de cultivo do setor. Os animais foram fixados com Karnovsky e dissecados. De cada animal, retiraram-se as antênulas, as antenas, as maxilas, as placas mandibulares, os três maxilípedes e os olhos para possibilitar a observação dos apêndices e as estruturas sensitivas. Os apêndices e olhos foram metalizados e fotodocumentados em microscópio eletrônico de varredura. Os olhos também foram analisados com técnicas de microscopia eletrônica de transmissão e técnica de rotina para análises histológicas segundo Behmer (2003). Identificaram-se setas sensitivas em todos os estágios larvais, pós-larva, juvenil e adulto. Elas distribuem-se em todos... / The crustaceans dispose of sensitive structures that allow them to receiive stimuli from environment. These are used to locate and capture food. Chemoreceprion and mechanoreption are known as the main senses used by the decapod crustaceans to indentify food particles. The Macrobrachium rosenbergii is a species that goes through a planktonic and a benthonic phase performs great migrations against or within the current depending on the life cycle phase or physiological stage and changes its feeding haits from carnivorous to omnivorous. Thus, it should present perception mechanisms of environment stimuli that are modified during development. Therefore, the hypotheisis brought up in this research was that the M. rosenbergii presents sensitive structures on the surface of the body and appendices that change from since the hatching of the larva up to the adult phase. The object of this paper was to research the occurrence of the sensitive structures during the entogenetic development of the M. rosenbergii. The research was performed at the carciniculture sector of the CAUNESP. The larvae and post larvae were collected from larvae culture under a closed dynamic system according to Valenti (1998) and the yong and adult larvae from the cultivating systems of the sector. The animals were set with Karnovsky and dissected. From each animal the antennules, the antennas, the maxillas, the mouthpiece plates, the three maxilipedes and the sensitve structures. The appendices and eyes were metalized and photo documented by way of electronic transmission techniques and rotine techniques for histological analysis according to Behmer (2003). Sencitive setae were identified in all larval stages, post larval, young and adult. They are distributed in all of the dissected appendices with Intense morphological variantions. They present. They present typical morphological pattern of the sensitive setae, with basal... (Complete abstract click electronic access below)

The human jaw, like all other articulated body parts, exhibits small oscillatory movements during isometric holding tasks. These movements, known as physiological tremor, arise as a consequence of the interaction of various factors. One of these factors is reflex feedback from peripheral receptors. In the human jaw, receptors that innervate the periodontium are able to transduce minute changes in force. This thesis examines the contribution of these periodontal mechanoreceptors (PMRs) to the genesis of physiological tremor of the human jaw. By using frequency domain analysis of time series recorded during isometric biting tasks, the character of physiological jaw tremor can be revealed. Physiological jaw tremor was observed in force recorded from between the teeth as well as from electromyograms recorded from the principal muscles of mastication. These recordings have shown us that jaw physiological tremor consists of a frequency invariant component between 6 and 10Hz. This frequency remains unaltered under various load conditions where the mechanical resonance of the jaw would be expected to vary greatly (Chapter 2). Such findings indicate a ‘neurogenic’ origin for this tremor. A possible candidate for this neurogenic component of physiological tremor in the jaw is the reflex feedback arising from the PMRs. Using local anaesthetisation, it has been shown in this thesis, that by blocking outflow from the PMRs, the amplitude of neurogenic physiological jaw tremor can be reduced dramatically. This procedure caused a dramatic reduction in not only the mechanical recordings of tremor but also in the coupling between masseteric muscles bilaterally (Chapter 3) and between single motor units recorded from within a homonymous muscle (Chapter 4). The obvious mechanism by which periodontal mechanoreceptor anaesthetisation could reduce the amplitude of physiological tremor in the jaw would be by reducing the amplitude of the oscillatory input to the motoneurones driving the tremor. This interpretation remains controversial however as physiological tremor in the jaw can be observed at force levels above which the PMRs are supposedly saturated in their response. In light of this knowledge, the saturating characteristics of these receptors in terms of reflex output were examined. To do this, a novel stimulation paradigm was devised whereby the incisal teeth were mechanically stimulated with identical stimulus waveforms superimposed upon increasing tooth preloads. This necessitated the use of a frequency response method to quantify the reflexes. An optimal frequency for stimulation was identified and used to confirm that the hyperbolic saturating response of PMRs observed previously, translated to a similar phenomenon in masticatory reflexes (Chapter 5). These data reinforced the idea that physiological tremor in the jaw was not just a consequence of rhythmic reflex input from PMRs, as the dynamic reflex response uncoupled from the input as the receptor-mediated reflex response saturated. An alternative hypothesis was then developed that suggested the effect of PMR suppression in physiological tremor was via tonic rather than rhythmic effects on the masseteric motoneurone pool. By utilising a novel contraction strategy to manipulate the mean firing rate of the motor neuron pool at a given level of force production, data contained in Chapter 6 shows that population motor unit firing statistics influence the expression of physiological tremor, and such manipulations mimic, to an extent, the changes in firing statistics and tremor amplitude seen during anaesthetisation of the PMRs. This thesis therefore posits a mechanism whereby periodontal input influences the firing rate of motoneurones in such a way as to promote tremulous activity (Chapter 5). However, as this proposed mechanism did not explain the full extent of tremor suppression seen during PMR anaesthetisation it can therefore only be considered a contributing factor in a multifactor process. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297555 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2007

The human jaw, like all other articulated body parts, exhibits small oscillatory movements during isometric holding tasks. These movements, known as physiological tremor, arise as a consequence of the interaction of various factors. One of these factors is reflex feedback from peripheral receptors. In the human jaw, receptors that innervate the periodontium are able to transduce minute changes in force. This thesis examines the contribution of these periodontal mechanoreceptors (PMRs) to the genesis of physiological tremor of the human jaw. By using frequency domain analysis of time series recorded during isometric biting tasks, the character of physiological jaw tremor can be revealed. Physiological jaw tremor was observed in force recorded from between the teeth as well as from electromyograms recorded from the principal muscles of mastication. These recordings have shown us that jaw physiological tremor consists of a frequency invariant component between 6 and 10Hz. This frequency remains unaltered under various load conditions where the mechanical resonance of the jaw would be expected to vary greatly (Chapter 2). Such findings indicate a ‘neurogenic’ origin for this tremor. A possible candidate for this neurogenic component of physiological tremor in the jaw is the reflex feedback arising from the PMRs. Using local anaesthetisation, it has been shown in this thesis, that by blocking outflow from the PMRs, the amplitude of neurogenic physiological jaw tremor can be reduced dramatically. This procedure caused a dramatic reduction in not only the mechanical recordings of tremor but also in the coupling between masseteric muscles bilaterally (Chapter 3) and between single motor units recorded from within a homonymous muscle (Chapter 4). The obvious mechanism by which periodontal mechanoreceptor anaesthetisation could reduce the amplitude of physiological tremor in the jaw would be by reducing the amplitude of the oscillatory input to the motoneurones driving the tremor. This interpretation remains controversial however as physiological tremor in the jaw can be observed at force levels above which the PMRs are supposedly saturated in their response. In light of this knowledge, the saturating characteristics of these receptors in terms of reflex output were examined. To do this, a novel stimulation paradigm was devised whereby the incisal teeth were mechanically stimulated with identical stimulus waveforms superimposed upon increasing tooth preloads. This necessitated the use of a frequency response method to quantify the reflexes. An optimal frequency for stimulation was identified and used to confirm that the hyperbolic saturating response of PMRs observed previously, translated to a similar phenomenon in masticatory reflexes (Chapter 5). These data reinforced the idea that physiological tremor in the jaw was not just a consequence of rhythmic reflex input from PMRs, as the dynamic reflex response uncoupled from the input as the receptor-mediated reflex response saturated. An alternative hypothesis was then developed that suggested the effect of PMR suppression in physiological tremor was via tonic rather than rhythmic effects on the masseteric motoneurone pool. By utilising a novel contraction strategy to manipulate the mean firing rate of the motor neuron pool at a given level of force production, data contained in Chapter 6 shows that population motor unit firing statistics influence the expression of physiological tremor, and such manipulations mimic, to an extent, the changes in firing statistics and tremor amplitude seen during anaesthetisation of the PMRs. This thesis therefore posits a mechanism whereby periodontal input influences the firing rate of motoneurones in such a way as to promote tremulous activity (Chapter 5). However, as this proposed mechanism did not explain the full extent of tremor suppression seen during PMR anaesthetisation it can therefore only be considered a contributing factor in a multifactor process. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297555 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2007