Si elegans: a computational model of C. elegans muscle response to light

It has long been the goal of computational neuroscientists to understand animal nervous systems, but their vast complexity has made it very difficult to fully understand even basic functions such as movement. The C. elegans nematode offers the opportunity to study a fully described connectome and link neural network to behaviour. In this paper a model of the responses of the body wall muscle in C. elegans to a random light stimulus is presented. An algorithm has been developed that tracks synapses in the nematode nervous system from the stimulus in the phototaxis sensory neurons to the muscles cells. A linear second order model was used to calculate the isometric force in each of the C. elegans body wall muscle cells. The isometric force calculated resembles that of previous investigations in muscle modelling

Characterisation of the biomechanical, passive, and active properties of femur-tibia joint leg muscles in the stick insect Carausius morosus

The understanding of locomotive behaviour of an animal necessitates the knowledge not only about its neural activity but also about the transformation of this activity patterns into muscle activity. The stick insect is a well studied system with respect to its motor output which is shaped by the interplay between sensory signals, the central neural networks for each leg joint and the coordination between the legs. The muscles of the FT (femur-tibia) joint are described in their morphologies and their motoneuronal innervation patterns, however little is known about how motoneuronal stimulation affects their force development and shortening behaviour. One of the two muscles moving the joint is the extensor tibiae, which is particularly suitable for such an investigation as it features only three motoneurons that can be activated simultaneously, which comes close to a physiologically occuring activation pattern. Its antagonist, the flexor tibiae, has a more complex innervation and a biomechanical investigation is only reasonable at full motoneuronal recruitment. Muscle force and length changes were measured using a dual-mode lever system that was connected to the cut muscle tendon. Both tibial muscles of all legs were studied in terms of their geometry: extensor tibiae muscle length changes with the cosine of the FT joint angle, while flexor tibiae length changes with the negative cosine, except for extreme angles (close to 30° and 180°). For all three legs, effective flexor tibiae moment arm length (0.564 mm) is twice that of the extensor tibiae (0.282 mm). Flexor tibiae fibres are 1.5 times longer (2.11 mm) than extensor tibiae fibres (1.41 mm). Active isometric force measurements demonstrated that extensor tibiae single twitch force is notably smaller than its maximal tetanical force at 200 Hz (2-6 mN compared to 100-190 mN) and takes a long time to decrease completely (> 140 ms). Increasing either frequency or duration of the stimulation extends maximal force production and prolongs the relaxation time of the extensor tibiae. The muscle reveals `latch´ properties in response to a short-term increase in activation. Its working range is on the ascending limb of the force-length relationship (see Gordon et al. (1966b)) with a shift in maximum force development towards longer fibre lengths at lower activation. The passive static force increases exponentially with increasing stretch. Maximum forces of 5 mN for the extensor, and 15 mN for the flexor tibiae occur within the muscles´ working ranges. The combined passive torques of both muscles determine the rest position of the joint without any muscle activity. Dynamically generated forces of both muscles can become as large as 50-70 mN when stretch ramps mimick a fast middle leg swing phase. FT joint torques alone (with ablated muscles) do not depend on FT joint angle, but on deflection amplitude and velocity. Isotonic force experiments using physiological activation patterns demonstrate that the extensor tibiae acts like a low-pass filter by contracting smoothly to fast instantaneous stimulation frequency changes. Hill hyperbolas at 200 Hz vary a great deal with respect to maximal force (P0) but much less in terms of contraction velocity (V0) for both tibial muscles. Maximally stimulated flexor tibiae muscles are on average 2.7 times stronger than extensor tibiae muscles (415 mN and 151 mN), but contract only 1.4 times faster (6.05 mm/s and 4.39 mm/s). The dependence of extensor tibiae V0 and P0 on stimulation frequency can be described with an exponential saturation curve. V0 increases linearly with length within the muscle´s working range. Loaded release experiments characterise extensor and flexor tibiae series elastic components as quadratic springs. The mean spring constant of the flexor tibiae is 1.6 times larger than of the extensor tibiae at maximal stimulation. Extensor tibiae stretch and relaxation ramps show that muscle relaxation time constant slowly changes with muscle length, and thus muscle dynamics have a long-lasting dependence on muscle length history. High-speed video recordings show that changes in tibial movement dynamics match extensor tibiae relaxation changes at increasing stimulation duration

On the intrinsic control properties of muscle and relexes: exploring the interaction between neural and musculoskeletal dynamics in the framework of the equilbrium-point hypothesis

The aim of this thesis is to examine the relationship between the intrinsic dynamics of the body and its neural control. Specifically, it investigates the influence of musculoskeletal properties on the control signals needed for simple goal-directed movements in the framework of the equilibriumpoint (EP) hypothesis. To this end, muscle models of varying complexity are studied in isolation and when coupled to feedback laws derived from the EP hypothesis. It is demonstrated that the dynamical landscape formed by non-linear musculoskeletal models features a stable attractor in joint space whose properties, such as position, stiffness and viscosity, can be controlled through differential- and co-activation of antagonistic muscles. The emergence of this attractor creates a new level of control that reduces the system’s degrees of freedom and thus constitutes a low-level motor synergy. It is described how the properties of this stable equilibrium, as well as transient movement dynamics, depend on the various modelling assumptions underlying the muscle model. The EP hypothesis is then tested on a chosen musculoskeletal model by using an optimal feedback control approach: genetic algorithm optimisation is used to identify feedback gains that produce smooth single- and multijoint movements of varying amplitude and duration. The importance of different feedback components is studied for reproducing invariants observed in natural movement kinematics. The resulting controllers are demonstrated to cope with a plausible range of reflex delays, predict the use of velocity-error feedback for the fastest movements, and suggest that experimentally observed triphasic muscle bursts are an emergent feature rather than centrally planned. Also, control schemes which allow for simultaneous control of movement duration and distance are identified. Lastly, it is shown that the generic formulation of the EP hypothesis fails to account for the interaction torques arising in multijoint movements. Extensions are proposed which address this shortcoming while maintaining its two basic assumptions: control signals in positional rather than force-based frames of reference; and the primacy of control properties intrinsic to the body over internal models. It is concluded that the EP hypothesis cannot be rejected for single- or multijoint reaching movements based on claims that predicted movement kinematics are unrealistic

Aspects of epimuscular myofascial force transmission : a physiological, pathological and comparative-zoological approach

Huijing, P.A.J.B.M. [Promotor

Aerospace Medicine and Biology: A cumulative index to the 1974 issues of a continuing bibliography

This publication is a cumulative index to the abstracts contained in supplements 125 through 136 of Aerospace Medicine and Biology: A Continuing Bibliography. It includes three indexes--subject, personal author, and corporate source

Coupling the mechanics and energetics of bird and insect flight

Humanity has long been fascinated by the mysteries of bird and insect flight, but only recently have we developed the technologies required to understand the complex mechanisms at work. These mechanisms range from molecular interactions to the interactions between whole organisms, encompassing a great number of mechanical and energetic processes. Research into animal flight has made great progress over the past half-century thanks to developments in technology and methodology, allowing for greater insights into the metabolic, mechanical and aerodynamic processes central to animal flight. Currently, there is a good understanding of several of these components but the topic of animal flight has been explored with a rather piecemeal approach and a more integrative understanding of the mechanics and energetics of animal flight is required. The research presented in this thesis aims to bridge our understanding of the often separately analysed mechanical and energetic aspects of animal flight and address key gaps in the existing knowledge. Many volant bird species exhibit asymmetrical wingbeat cycles such that the flight muscles spend relatively more time shortening than lengthening. Through the simultaneous determination of mechanical work generation and energy consumption in the mouse soleus during in vitro contraction cycles with asymmetrical length trajectories, we reveal that mechanical power production can be increased by increasing the proportion of the cycle spent shortening without sacrificing net muscle efficiency. These experiments also served to validate a methodology for estimating the net muscle efficiency of the avian pectoralis muscle. The following experiments determined the mechanical power generation, muscular costs of contraction and muscle efficiency of the budgerigar pectoralis during a range of simulated flight speeds. The efficiency of avian flight muscle was previously unknown and unsubstantiated values had been used in common predictive models of flight energetics. It was found that avian flight muscle efficiency is approximately 21% during the downstroke and remains constant with flight speed, with muscular energy consumption and power generation sharing characteristics with whole-animal metabolic and mechanical power-speed relationships. The consequences of these findings for the estimation of energetic flight costs are discussed. While respirometry serves as the gold standard for measuring metabolic expenditure during activity, accelerometry affords the potential for estimating the energetic costs of flight in birds in the field. However, there has been no calibration of the relationship between body acceleration and energy expenditure. By measuring energy consumption via respirometry and dynamic body acceleration in masked lovebirds during wind tunnel flights at a range of speeds, we determine the metabolic requirements of flight for a new avian species and validate the use of accelerometry for estimating energy expenditure and flight kinematics. Finally, we examined the previously unexplored relationship between myoplasmic calcium ion concentration, contraction frequency, mechanical power and myofibrillar efficiency in asynchronous insect flight muscles. There is increasing evidence to suggest that calcium plays an important role in the modulation of mechanical power during flight in insects with asynchronous flight muscles. By simultaneously measuring mechanical power generation and ATPase activity of flight muscles from giant waterbugs (Lethocerus), we reveal a positively shifting relationship between increasing calcium concentrations and optimal frequency for generating power, but with no evidence of a shift in optimal frequency for muscle efficiency. This research demonstrates scientific impact by improving our understanding of the factors that affect muscle efficiency, refining the models used to predict wild animal metabolism during flight, developing and validating existing experimental techniques for determining the costs of flight, and improving our understanding of how both mechanical and physiological factors can affect the mechanical and energetic performance of bird and insect flight muscles

Characterising the neck motor system of the blowfly

Flying insects use visual, mechanosensory, and proprioceptive information to control their movements, both when on the ground and when airborne. Exploiting visual information for motor control is significantly simplified if the eyes remain aligned with the external horizon. In fast flying insects, head rotations relative to the body enable gaze stabilisation during highspeed manoeuvres or externally caused attitude changes due to turbulent air. Previous behavioural studies into gaze stabilisation suffered from the dynamic properties of the supplying sensor systems and those of the neck motor system being convolved. Specifically, stabilisation of the head in Dipteran flies responding to induced thorax roll involves feed forward information from the mechanosensory halteres, as well as feedback information from the visual systems. To fully understand the functional design of the blowfly gaze stabilisation system as a whole, the neck motor system needs to be investigated independently. Through X-ray micro-computed tomography (μCT), high resolution 3D data has become available, and using staining techniques developed in collaboration with the Natural History Museum London, detailed anatomical data can be extracted. This resulted in a full 3- dimensional anatomical representation of the 21 neck muscle pairs and neighbouring cuticula structures which comprise the blowfly neck motor system. Currently, on the work presented in my PhD thesis, μCT data are being used to infer function from structure by creating a biomechanical model of the neck motor system. This effort aims to determine the specific function of each muscle individually, and is likely to inform the design of artificial gaze stabilisation systems. Any such design would incorporate both sensory and motor systems as well as the control architecture converting sensor signals into motor commands under the given physical constraints of the system as a whole.Open Acces

The phenotypic plasticity of whole animal and muscle performance during fast-starts in Cottidae

Chapter 1. Fast-starts are used by most fish species in order to capture prey and escape predators. An introduction to this mode of fish locomotion and the structure and function of the muscle powering swimming movements, is given. Temperature has the potential to alter fast-start behaviour at various levels of organisation ranging from the whole animal to the molecular and can act over time scales extending from the immediate to the evolutionary. The thermal dependence of fast-start performance is discussed. Chapter 2. The effects of acclimation and acute temperature on the kinematics of the escape response in two species of maidne Cottidae, the short-horn sculpin (Myoxocephalus scorpius L.) and the long-spined sea scorpion (Taurulus bubalis Euphr.) were examined. Hypotheses were formulated based on relevant studies and the natural history of the fish to test the idea that seasonal temperature acclimation conferred a fitness advantage and to examine whether acclimation responses were constant through development. Chapter 3. The effect of seasonal thermal acclimation on the in vivo strain and power output of the fast muscle fibres during escape responses in the short- horn sculpin was examined. Chapter 4. The kinematics, in vivo muscle action, power output and energetics of escape and prey capture responses in the short-horn sculpin are discussed. Fast-starts were filmed using high speed video synchronised with sonomicrometry and EMG. The in vivo muscle strain and activation recordings were abstracted for use in work loop experiments. Changes in the metabolic substrates following work loops from the two different types of fast-starts were analysed using high performance liquid chromatography (HPLC). Chapter 5 The velocity of the wave of curvature passing down the fish and the power requirements during fast-start escape responses were calculated non-invasively. This was carried out on both cottid species acclimated to 5 and 15 ° and filmed using high speed cinematography at 0.8, 5.0, 15.0 and 20.0 °. The power requirements for the contralateral contraction were 20 W. kg-1 muscle in 5 °-acclimated fish escaping at 5 ° and 58 W. kg-1 muscle in 15 °-acclimated fish swimming at 15 °. Comparative values of power output measured from work loop experiments in Chapter 3 were 33 and 66 W.kg-1 respectively

Aerospace Medicine and Biology: A continuing bibliography with indexes (supplement 134)

This special bibliography lists 301 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System in October 1974

Decoding and encoding of neural signals for peripheral interfaces

Monografia (graduação)—Universidade de Brasília, Faculdade de Tecnologia, Curso de Graduação em Engenharia de Controle e Automação, 2015.O campo da neuroengenharia cresce a cada dia com estudos promissores sobre suas diferentes áreas, sendo uma delas a estimulação elétrica funcional (FES). Para o avanço desses estudos, diferentes plataformas experimentais biológicas são utilizadas a fim de melhor entender o funcionamento do sistema nervoso e, eventualmente, poder intervir ativamente a fim de recuperar funções perdidas devido a patologias ou acidentes. Além disso, para o melhor estudo da área, diversos pesquisadores se utilizam de artrópodes como insetos. Estas cobaias são muito úteis, devido às suas similaridades nervosas com seres mais complexos e facilidade de manuseio e aquisição. Desta forma, além de serem utilizados em pesquisas que se utilizam de seus tamanhos reduzidos e complexidade biomecânica para realizar tarefas difíceis para a micro-robótica atual, os insetos também são utilizados para estudos introdutórios em neuroengenharia. Neste trabalho, duas plataformas experimentais relativas aos dois cenários descritos para estimulação em nervos são desenvolvidas e testadas – ambas serão aprofundadas brevemente a seguir, a começar pela última. No Laboratório de Automação e Robótica (LARA da Universidade de Brasília (UnB), foi desenvolvida uma plataforma experimental para implementação de algoritmos de controle de direção para baratas da espécie Blaberus giganteus. Esse setup contou com o kit de desenvolvimento da Backyard Brains, o RoboRoach, afixado às costas da barata a ser experimentada para estimulação elétrica de nervos de suas antenas. A placa RoboRoach foi interfaceada com um computador pessoal (PC) por meio de protocolo Bluetooth (BT) 4.0, onde o algoritmo de orientação foi implementado e executado. O PC foi também ligado a um sensor de captura de movimento da NDI Digital, o Polaris Spectra. Este sensor, por meio de emissão e recebimento de ondas infravermelhas, provia ao PC informações de posição do marcador passivo afixado à placa nos três eixos de deslocamento. Desta forma, traçada uma referência retilínea, umalgoritmo de orientação simples foi implementado de forma a estimular a antena da barata referente ao lado para a qual esta não deveria ir, fazendo uso de um comportamento evasivo gatilhado pelas antenas das baratas. Assim, a barata poderia ser orientada a seguir uma trajetória retilínea. Um controlador proporcional, ainda, foi implementado de forma que a amplitude de estimulação variasse de acordo com o distanceamento da barata em relação à referência desejada. Para os experimentos, foi utilizada inicialmente uma "barata virtual", referente à utilização de diodos emissores de luz (LEDs) de debug presentes na placa, que indicavam qual antena estaria sendo estimulada em determinado instante. Com isso, foi possível validar a eficiência do controlador em si, isolando as variáveis referentes à estimulação da barata. Em seguida, os procedimentos cirúrgicos para experimentação com as baratas foram feitos e os experimentos foram executados. Os resultados adquiridos dos experimentos mostraram que, apesar do algoritmo de controle se comportar bem em um cenário simulado (da "barata virtual"), houve impedimentos em relação à estimulação dos espécimes. Erros na forma como o setup experimental foi desenvolvido e a estimulação foi feita foram encontrados e discutidos. Mesmo assim, resultados satisfatórios no controle de direção das baratas foram obtidos. O trabalho foi, então, prosseguido no Centro de Neuroengenharia (CNE) da Universidade de Utah. No novo setup experimental, foi desenvolvido um sistema em tempo real utilizado Matlab em um sistema operacional Windows 7. O sistema interfaceava com um hardware de nome Grapevine, da Ripple LLC, que provia dados de eletromiografia adquiridos por uma de suas entradas e, além disso, possibilitava modulação de parâmetros de estimulação elétrica em uma de suas saídas. Desta forma, o sistema foi montado em diversas sessões experimentais: inicialmente, para validação do sistema em tempo real, se utilizando de sapos (de gênero Ptychadena) e, posteriormente, para desenvolvimento da plataforma experimental e implementação do algoritmo de controle, ratos (Sprague-Dawley). Ambos os grupos de espécimes foram estimulados no nervo ciático utilizando um eletrodo do tipo hook, de forma a desencadear uma estimulação de nervo completo (whole-nerve stimulation). Os sinais elétricos, assim, ativavam grupos musculares específicos e os sinais elétricos que resultavam em contrações foram gravados e utilizados no sistema de controle. O setup contou, ainda, com a denervação de ramificações do nervo ciático, de forma a isolar o tipo de movimento causado pela estimulação, e com a consequente utilização de um sensor de força analógico para posterior comparação offline com os sinais elétricos lidos do músculo (evoked electromyography – eEMG). O algoritmo de controle proposto se utilizava de uma curva de recrutamento gerada por meio de variações de amplitude dos sinais de estimulação e o valor máximo absoluto (MAV) das respectivas respostas musculares. Esse procedimento era feito anteriormente à execução do controle, uma vez que este gerava a curva utilizada durante a execução do algoritmo de controle. Este consistia de leituras a cada 20ms (verificados em suas consistências posteriormente) dos sinais de eEMG, cálculo do respectivo MAV e utilização deste na função de controle. Anteriormente a esta, o valor atual de referência era computado, de forma a respeitar a forma trapezoidal desejada, de valores mínimo e máximo entre zero e 50% do valor de saturação da curva de recrutamento. O controle proporcional integral era, então, computado com base no erro entre valor esperado e referência e a variável de saída somada à referência desejada. Uma vez com o valor normalizado final, este era utilizado na função inversa da curva de recrutamento e o valor de amplitude a ser utilizado para estimulação era computado. Foram adquiridos resultados referentes à consistência do sistema em tempo real e, ainda, à eficiência do controle implementado. Apesar da discussão sobre consistência do período de amostragem se mostrar curta, uma vez que os 20ms esperados foram respeitados com uma pequena faixa de erro, muitos pontos em relação aos resultados obtidos do controle são discutidos. Qualidade da curva de recrutamento, efeitos da exposição do nervo ao ambiente, qualidade do controle utilizando diferentes ganhos proporcionais e integrais, relação entre eEMG lido e força resultante, estratégias de filtragem implementadas, fadiga muscular observada e erros de implementação do controle são discutidos. Por fim, conclui-se que, apesar do sistema experimental (hardware e software) e do algoritmo de controle poderem ser melhorados no futuro, houve sucesso no desenvolvimento do setup e na implementação do algoritmo de controle.This work consists on the development of two experimental setups for the implementation of control algorithms in animals. The first one, developed at the Automation and Control Laboratory at theUniversity of Brasilia, consists on the electrical stimulation of antennal nerves of cockroaches (Blaberus giganteus) for direction control based on a retilinear reference. The position of the cockroach was measured by a motion capture system, which communicated with a personal computer (PC) running the control algorithm. The PC communicated with the stimulation board fixed to the cockroach back through Bluetooth 4.0 protocol. The control algorithm implemented was a simple line-follower which steer the cockroach by stimulating the antenna contrary to the desired direction with an amplitude proportional to the error between measured and reference positions. The second experimental setup took place at the Center for Neural Engineering at the University of Utah, where experiments using grass frogs and Sprague-Dawley rats were conducted. For both species, a hook electrode was used for whole-nerve stimulation of the sciatic nerve and wire electrodes were inserted into gastrocnemius muscles in order to record evoked electromyography (eEMG) singals. A proportional integral control algorithm was implemented in order to control muscle activation based on maximum absolute value (MAV) of the eEMG measured and recruitment curves found beforehand. Several aspects were discussed for both experimental setups regarding efficiency of the controllers and problems found in development and implementation. Finally, it is concluded that, even though there are several aspects to be explored in relation to improvements in both projects, the results found were satisfactory for initial trials