Onecut-dependent Nkx6.2 transcription factor expression is required for proper formation and activity of spinal locomotor circuits.

In the developing spinal cord, Onecut transcription factors control the diversification of motor neurons into distinct neuronal subsets by ensuring the maintenance of Isl1 expression during differentiation. However, other genes downstream of the Onecut proteins and involved in motor neuron diversification have remained unidentified. In the present study, we generated conditional mutant embryos carrying specific inactivation of Onecut genes in the developing motor neurons, performed RNA-sequencing to identify factors downstream of Onecut proteins in this neuron population, and employed additional transgenic mouse models to assess the role of one specific Onecut-downstream target, the transcription factor Nkx6.2. Nkx6.2 expression was up-regulated in Onecut-deficient motor neurons, but strongly downregulated in Onecut-deficient V2a interneurons, indicating an opposite regulation of Nkx6.2 by Onecut factors in distinct spinal neuron populations. Nkx6.2-null embryos, neonates and adult mice exhibited alterations of locomotor pattern and spinal locomotor network activity, likely resulting from defective survival of a subset of limb-innervating motor neurons and abnormal migration of V2a interneurons. Taken together, our results indicate that Nkx6.2 regulates the development of spinal neuronal populations and the formation of the spinal locomotor circuits downstream of the Onecut transcription factors

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 217, March 1981

Approximately 130 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1981 are included in this bibliography. Topics include aerospace medicine and biology

Volumetric Flow Imaging Reveals the Importance of Vortex Ring Formation in Squid Swimming Tail-First and Arms-First

Squids use a pulsed jet and fin movements to swim both arms-first (forward) and tail-first (backward). Given the complexity of the squid multi-propulsor system, 3D velocimetry techniques are required for the comprehensive study of wake dynamics. Defocusing digital particle tracking velocimetry, a volumetric velocimetry technique, and high-speed videography were used to study arms-first and tail-first swimming of brief squid Lolliguncula brevis over a broad range of speeds [0-10 dorsal mantle lengths (DML) s-1) in a swim tunnel. Although there was considerable complexity in the wakes of these multi-propulsor swimmers, 3D vortex rings and their derivatives were prominent reoccurring features during both tail-first and arms-first swimming, with the greatest jet and fin flow complexity occurring at intermediate speeds (1.5-3.0 DML s-1). The jet generally produced the majority of thrust during rectilinear swimming, increasing in relative importance with speed, and the fins provided no thrust at speeds \u3e4.5 DML s-1. For both swimming orientations, the fins sometimes acted as stabilizers, producing negative thrust (drag), and consistently provided lift at low/intermediate speeds (\u3c2.0 DML s-1) to counteract negative buoyancy. Propulsive efficiency (η) increased with speed irrespective of swimming orientation, and eta for swimming sequences with clear isolated jet vortex rings was significantly greater (η=78.6 +/- 7.6%, mean +/- s.d.) than that for swimming sequences with clear elongated regions of concentrated jet vorticity (η=67.9 +/- 19.2%). This study reveals the complexity of 3D vortex wake flows produced by nekton with hydrodynamically distinct propulsors

Development of muscle structure and function in loliginid squids

Squid embryos are able to contract their mantle early during the embryonic period. This dissertation examines the onset of contractile capabilities and subsequent maturation of the main locornotor structures in embryos of two species of loligind squids with a focus on the mantle musculature. The functional implications of the differentiation and organization of the musculature is investigated. The results of these series of studies indicate that the development and emergence of functional competence of the mantle musculature in loliginid squids is a dynamic process. Differentiation and organization of the musculature of the main locomotor structures does not occur simultaneously and has a precise sequence with the mantle developing first, then funnel and the fins developing and organizing last. The superficial mitochodria rich (SMR) fibers that drive respiratory contractions differentiate first at the inner and outer surfaces of the mantle. The central mitochondria poor (CMP) muscle fibers, which are active during fast and escape jetting, differentiate second and in the central region of the mantle. The mantle of embryonic loligind squids is able to produce contractions in the absence of a completely developed and organized musculature. During subsequent stages, the mantle undergoes measurable ontogenetic kinematic changes as evidenced by an increase in the frequency and duration of the contractions. Moreover, mathematical modeling of these contractions indicates that the mantle in embryonic squids is capable of producing two distinct types of contractions. These different contraction types resemble the respiratory and locomotory contractions of the juveniles and adults. When these data are examined in conjunction with the morphological data they show that mantle morphology and mantle functional ability appear to be developing in parallel. Additionally, stage 27 emerges as a morphologically and functionally significant point in development. Stage 27 embryos have a robust, differentiated mantle whose morphological organization and functional repertoire begins to reflect that of the adults. (Abstract shortened by UMI.)

Musculoskeletal modeling and finite element analysis of the proximal juvenile femur

The influence of mechanical loading on bone modelling and remodelling has been, and still is the subject of many studies. It is widely accepted that the internal structure of long bones is orientated to the strains experienced throughout activities, and the morphometry of the bones are as a result of the loading. Although other influences play a role in bone development including, hormonal, nutritional and genetic. The internal structure is orientated in such a way that it transfers the loads experienced without being excessive in weight, providing an efficient weight bearing structure. Many researchers have analysed the adult femur but little work has been undertaken to understand femoral development in juveniles. Therefore the aim this work was to develop an understanding of the mechanical stresses and strains that the femur experiences during growth.The juvenile femur changes dramatically throughout growth. These changes occur from prenatal through to full maturity. The most notable include the ossification from a highly cartilaginous structure in the early years of development, to bone at ~18 years old, an increase in the length and angle of the neck, a change in the shaft torsion and a change in the bicondylar angle. Similarly, the development of movement patterns and locomotion in humans changes significantly throughout growth. Movement is restricted in utero, in neonates the movement begins to engage muscular activity, at 6 months a baby is usually able to sit upright; 9 months crawling begins; by 1 year old there is the ability to walk without support and at 4 years old an adult like gait pattern has developed. Full adult gait pattern has been documented to be achieved between 8-11 years old.In this work through gait analysis and musculoskeletal modelling the loads which the femur experiences at specific stages/ages of bipedal locomotion are analysed. Finite element analyses were then performed to develop an understanding of the stresses and strains of the proximal juvenile femur in relation to the attainment and development of bipedal gait. This was achieved by evaluating changes in these mechanical stresses and strains throughout different ages, relating them to the variations discovered in the gait patterns.Digitisation of the femora was performed on four specimens; prenatal, 3 years old, 7 years old and an adult. Following the scanning of the specimens in a micro CT scanner, some restoration to the damaged samples was required. Furthermore the dry samples were incomplete, and the models were needed to be modelled to accurately resemble fully intact femurs. The CT scans contained the full shaft however were missing the fully articulated proximal femur, due to the dry nature of the specimens the cartilages were absent. MRI scans which contained the femoral head data but were missing the full shaft were merged with the CT data to create a fully articulated femur for use in subsequent modelling.Gait analysis was performed on five children aged from 3-7 years old, with an average of five adults gait data used for comparison. The analysis showed that kinematic data was similar between all ages, however kinetic results revealed some differences. Ground reaction force in the 3 year old showed a higher heel strike compared to a higher toe off observed in adult during the gait cycle, indicating a lack of control in the 3 year old. Furthermore the 3 year old, compared to the other ages, had different values in joint moments. These joint moment results in particular played a role in the muscle forces produced from the musculoskeletal modelling.To obtain the muscle force data required for the FEA, musculoskeletal models were built. Testing the reliability of the musculoskeletal model was performed comparing the kinematic and kinetic data from the musculoskeletal modelling against the data obtained from the motion capture system. A good agreement was found between these data sets with the kinematics having the largest difference in the ankle plantar flexion of 8.6°. The kinetic results revealed almost exact matches. Further testing was attempted between the muscle force data and collected EMG. The collected EMG matched reported EMG in the literature and the onset and offset times of muscle activity corresponded well to muscle force peaks produced in the musculoskeletal model. Comparisons between the EMG and force through calculating the EMG as a force were inconclusive, although a degree of accuracy was shown but a more comprehensive method is required. It was concluded that with the accuracy of the kinematic and kinetic results the musculoskeletal modelling was accurate enough to give a true representation of physiological muscle forces to be modelled during FEA.Analysis of the musculoskeletal modelling results in the children revealed that the 3 year old had the highest significance between all the age groups. With the greatest significance in the hip flexors and abductors throughout the gait cycle. Joint reaction forces as a percentage of bodyweight were found to be much higher in the juvenile models. The adult model had a value of 265% bodyweight whereas the 3 year old showed a reaction force of 537% bodyweight. These differences observed in the musculoskeletal modelling had a direct effect on the FEA because the loads calculated here were applied to the finite element models to evaluate the effects that these would have on the stresses and strains during growth and development of the femur.FE models were built to represent a 3 year old, 7 year old and adult femur. Age specific loads calculated over 100% of a gait cycle, were applied to the models. The stress/strain analysis revealed some differences between the models but in general the areas exposed to high and low strain levels were similar. The similarities could suggest that each model was structurally adapted to the loads the femur regularly experiences. The thesis was successful in evaluating the stress and strain distribution apparent in the developing femur. However the work would be advanced by evaluating models from age ranges with a much more varied movement pattern i.e. crawling. This would increase an understanding of the structural optimisation of the femur

Longitudinal and transversal displacements between triceps surae muscles during locomotion of the rat

The functional consequences of differential muscle activation and contractile behavior between mechanically coupled synergists are still poorly understood. Even though synergistic muscles exert similar mechanical effects at the joint they span, differences in the anatomy, morphology and neural drive may lead to non-uniform contractile conditions. This study aimed to investigate the patterns of activation and contractile behavior of triceps surae muscles, to understand how these contribute to the relative displacement between the one-joint soleus (SO) and two-joint lateral gastrocnemius (LG) muscle bellies and their distal tendons during locomotion in the rat. In seven rats, muscle belly lengths and muscle activation during level and upslope trotting were measured by sonomicrometry crystals and electromyographic electrodes chronically implanted in the SO and LG. Length changes of muscle-tendon units (MTUs) and tendon fascicles were estimated based on joint kinematics and muscle belly lengths. Distances between implanted crystals were further used to assess longitudinal and transversal deformations of the intermuscular volume between the SO and LG. For both slope conditions, we observed differential timing of muscle activation as well as substantial differences in contraction speeds between muscle bellies (maximal relative speed 55.9 mm s-1). Muscle lengths and velocities did not differ significantly between level and upslope locomotion, only EMG amplitude of the LG was affected by slope. Relative displacements between SO and LG MTUs were found in both longitudinal and transversal directions, yielding an estimated maximal length change difference of 2.0 mm between their distal tendons. Such relative displacements may have implications for the force exchanged via intermuscular and intertendinous pathways

Comparative aspects of the control of posture and locomotion in the spider crab Libinia emarginata

The study of pedestrian locomotion in crustaceans has largely focused on forward walking macrurans, or sideway walking brachyurans. The spider crab, Libinia emarginata is a brachyuran that, unlike its close relatives, preferentially walks forward. The phylogenetic position, behavioral preference, and amenability to experimental techniques make spider crabs an attractive model for comparative studies of crustacean locomotion. This dissertation looks at the neuroethology of forward walking in L. emarginata. I described the skeletal, muscular, and neural anatomy of the walking machinery of L. emarginata and found adaptations at each level that reflect its walking preference. The ranges of motion of leg joints aiding in forward locomotion were larger for spider crabs than for sideway walking crabs. The leg segments housing the musculature moving these joints were also larger. The proximal leg musculature consists of multiple muscle heads that can be activated independently during locomotion. The motor neurons innervating this musculature exhibited features of distantly related species that walk forward. Unlike many brachyurans, spider crabs use all ten legs during walking. Kinematic characterization of forward walking in L. emarginata showed that anterior and posterior limbs perform different functions during walking. Cross-correlation analysis among the leg joints of spider crabs revealed that distant joints have stronger coupling than adjacent ones. Neuroethology studies of pedestrian locomotion use multiple approaches. In order to understand how adaptive behavior is produced, it is necessary to study how the neural, muscular, and skeletal systems of an organism interact during its performance

Generating whole body movements for dynamics anthropomorphic systems under constraints

Cette thèse étudie la question de la génération de mouvements corps-complet pour des systèmes anthropomorphes. Elle considère le problème de la modélisation et de la commande en abordant la question difficile de la génération de mouvements ressemblant à ceux de l'homme. En premier lieu, un modèle dynamique du robot humanoïde HRP-2 est élaboré à partir de l'algorithme récursif de Newton-Euler pour les vecteurs spatiaux. Un nouveau schéma de commande dynamique est ensuite développé, en utilisant une cascade de programmes quadratiques (QP) optimisant des fonctions coûts et calculant les couples de commande en satisfaisant des contraintes d'égalité et d'inégalité. La cascade de problèmes quadratiques est définie par une pile de tâches associée à un ordre de priorité. Nous proposons ensuite une formulation unifiée des contraintes de contacts planaires et nous montrons que la méthode proposée permet de prendre en compte plusieurs contacts non coplanaires et généralise la contrainte usuelle du ZMP dans le cas où seulement les pieds sont en contact avec le sol. Nous relions ensuite les algorithmes de génération de mouvement issus de la robotique aux outils de capture du mouvement humain en développant une méthode originale de génération de mouvement visant à imiter le mouvement humain. Cette méthode est basée sur le recalage des données capturées et l'édition du mouvement en utilisant le solveur hiérarchique précédemment introduit et la définition de tâches et de contraintes dynamiques. Cette méthode originale permet d'ajuster un mouvement humain capturé pour le reproduire fidèlement sur un humanoïde en respectant sa propre dynamique. Enfin, dans le but de simuler des mouvements qui ressemblent à ceux de l'homme, nous développons un modèle anthropomorphe ayant un nombre de degrés de liberté supérieur à celui du robot humanoïde HRP2. Le solveur générique est utilisé pour simuler le mouvement sur ce nouveau modèle. Une série de tâches est définie pour décrire un scénario joué par un humain. Nous montrons, par une simple analyse qualitative du mouvement, que la prise en compte du modèle dynamique permet d'accroitre naturellement le réalisme du mouvement.This thesis studies the question of whole body motion generation for anthropomorphic systems. Within this work, the problem of modeling and control is considered by addressing the difficult issue of generating human-like motion. First, a dynamic model of the humanoid robot HRP-2 is elaborated based on the recursive Newton-Euler algorithm for spatial vectors. A new dynamic control scheme is then developed adopting a cascade of quadratic programs (QP) optimizing the cost functions and computing the torque control while satisfying equality and inequality constraints. The cascade of the quadratic programs is defined by a stack of tasks associated to a priority order. Next, we propose a unified formulation of the planar contact constraints, and we demonstrate that the proposed method allows taking into account multiple non coplanar contacts and generalizes the common ZMP constraint when only the feet are in contact with the ground. Then, we link the algorithms of motion generation resulting from robotics to the human motion capture tools by developing an original method of motion generation aiming at the imitation of the human motion. This method is based on the reshaping of the captured data and the motion editing by using the hierarchical solver previously introduced and the definition of dynamic tasks and constraints. This original method allows adjusting a captured human motion in order to reliably reproduce it on a humanoid while respecting its own dynamics. Finally, in order to simulate movements resembling to those of humans, we develop an anthropomorphic model with higher number of degrees of freedom than the one of HRP-2. The generic solver is used to simulate motion on this new model. A sequence of tasks is defined to describe a scenario played by a human. By a simple qualitative analysis of motion, we demonstrate that taking into account the dynamics provides a natural way to generate human-like movements

On the functional morphology and locomotion of the two-toed sloth (Choloepus didactylus, Xenarthra)

The evolution of extant sloths included the transition from a pronograde quadrupedal posture to an obligatory quadrupedal suspensory posture and locomotion at some point in their natural history. Recent phylogenetic analyses suggest only a distant relationship of the two extant genera and imply a convergent evolution of the sloth-like posture and locomotion. Due to the quadrupedal ‘upside-down’ posture and locomotion and thus inverse orientation of the body in regard of the force of gravity sloths represent a natural experiment to investigate the influence of gravity on the mammalian locomotor apparatus. This dissertation aims to contribute to the understanding of the evolution of the ‘upside-down’ posture of sloths, and, more generally, to the understanding of the influence of gravity on the mammalian locomotor apparatus.Während der Evolution der heutigen Faultiere kam es zu einem Übergang von einer pronograden quadrupeden Körperhaltung und Fortbewegung hin zu einer obligat quadruped-suspensorischen Körperhaltung und Fortbewegung. Neuere phylogenetische Studien legen nahe, dass diese für Faultiere typische Körperhaltung und Fortbewegung zweimalig unabhängig, also konvergent, entstanden ist. Aufgrund der quadruped-suspensorischen Körperhaltung und der damit umgekehrten Ausrichtung des Körpers zur Gravitation, repräsentieren die Faultiere darüber hinaus ein ‚natürliches Experiment’, dessen Untersuchung Einblicke in den Einfluss der Gravitation auf den Körper verspricht. Diese Dissertationsschrift hat zum Ziel zum Verständnis der Evolution der quadruped-suspensorischen Körperhaltung und Fortbewegung beizutragen und das Verständnis des Einflusses der Gravitation auf den Bewegungsapparat der Säugetiere zu verbessern