Static Forces and Moments Generated in the Insect Leg: Comparison of a Three-Dimensional Musculo-Skeletal Computer Model With Experimental Measurements

As a first step towards the integration of information on neural control, biomechanics and isolated muscle function, we constructed a three-dimensional musculo-skeletal model of the hind leg of the death-head cockroach Blaberus discoidalis. We tested the model by measuring the maximum force generated in vivo by the hind leg of the cockroach, the coxa-femur joint angle and the position of this leg during a behavior, wedging, that was likely to require maximum torque or moment production. The product of the maximum force of the leg and its moment arm yielded a measured coxa-femur joint moment for wedging behavior. The maximum musculo-apodeme moment predicted by summing all extensor muscle moments in the model was adequate to explain the magnitude of the coxa-femur joint moment produced in vivo by the cockroach and occurred at the same joint angle measured during wedging. Active isometric muscle forces predicted from our model varied by 3.5-fold among muscles and by as much as 70% with joint angle. Sums of active and passive forces varied by less than 3.5% over the entire range of possible joint angles (0-125º). Maximum musculo-apodeme moment arms varied nearly twofold among muscles. Moment arm lengths decreased to zero and switched to the opposite side of the center of rotation at joint angles within the normal range of motion. At large joint angles (\u3e100º), extensors acted as flexors. The effective mechanical advantage (musculo-apodeme moment arm/leg moment arm = 0.10) resulted in the six femoral extensor muscles of the model developing a summed force (1.4N) equal to over 50 times the body weight. The model\u27s three major force-producing extensor muscles attained 95% of their maximum force, moment arm and moment at the joint angle used by the animal during wedging

A Motor and a Brake: Two Leg Extensor Muscles Acting at the Same Joint Manage Energy Differently in a Running Insect

The individual muscles of a multiple muscle group at a given joint are often assumed to function synergistically to share the load during locomotion. We examined two leg extensors of a running cockroach to test the hypothesis that leg muscles within an anatomical muscle group necessarily manage (i.e. produce, store, transmit or absorb) energy similarly during running. Using electromyographic and video motion-analysis techniques, we determined that muscles 177c and 179 are both active during the first half of the stance period during muscle shortening. Using the in vivo strain and stimulation patterns determined during running, we measured muscle power output. Although both muscles were stimulated during the first half of shortening, muscle 177c generated mechanical energy (28 W kg–1) like a motor, while muscle 179 absorbed energy (–19 W kg–1) like a brake. Both muscles exhibited nearly identical intrinsic characteristics including similar twitch kinetics and force–velocity relationships. Differences in the extrinsic factors of activation and relative shortening velocity caused the muscles to operate very differently during running. Presumed redundancy in a multiple muscle group may, therefore, represent diversity in muscle function. Discovering how muscles manage energy during behavior requires the measurement of a large number of dynamically interacting variables

Die tatsächliche Versorgung von Frühgeborenen mit einem Gestationsalter von < 28 Schwangerschaftswochen oder einem Geburtsgewicht von < 1000 Gramm mit Cholin und die Korrelation dieser Versorgung mit der neurokognitiven Entwicklung im Alter von 2 Jahren

Als wesentlicher Bestandteil aller Membran- und Sekretphospholipide (Phosphatidylcholin, Sphingomyelin), sowie als Vorläufermolekül des Neurotransmitters Acetylcholin, spielt Cholin eine bedeutende Rolle in der Differenzierung und Funktion des zentralen Nervensystems. Tierstudien legen nahe, dass insbesondere die adäquate Cholinversorgung in einer frühen perinatalen Phase essentiell für die Entwicklung kognitiver Leistungen ist. Während die Bedeutung des Cholins für die fetale und neonatale Entwicklung allgemein anerkannt ist, wurde seiner Rolle in der Ernährung Frühgeborener bisher nicht viel Aufmerksamkeit zuteil. Ziel dieser Arbeit war es, einen möglichen Zusammenhang zwischen der Versorgung Frühgeborener mit Cholin und der neurokognitiven Entwicklung dieser Kinder aufzuzeigen. Dazu wurde die tatsächliche Cholinzufuhr im Rahmen des postnatalen Klinikaufenthalts von 93 in den Jahren 2006 und 2007 am Universitätsklinikum Tübingen geborenen Frühgeborenen mit einem Geburtsgewicht von < 1000 g oder einem Gestationsalter von < 28 SSW aus den Patientenkurven ermittelt. Zusätzlich wurde die Versorgung mit weiteren Mikro- (Folsäure, Methionin) und Makronährstoffen (Eiweiß, Fett, Kohlenhydrate) untersucht. Es wurde deutlich, dass die Zufuhr an Makronährstoffen unter den 2006/2007 am Uniklinikum Tübingen gültigen Ernährungsregimes die Anforderungen der damals gültigen Ernährungsleitlinien erfüllte, während hingegen die Gesamtcholinzufuhr innerhalb der ersten 28 Lebenstage nur in 2% der Fälle im Bereich der berechneten adäquaten Zufuhr von mindestens 27,4 mg/kg/d lag. Diese Unterversorgung mit Cholin war einerseits der Unreife des Gastrointestinaltrakts der Extremfrühgeborenen geschuldet, welche einen enteralen Nahrungsaufbau teilweise stark verzögerte. Zum anderen traten bei einzelnen Frühgeborenen durch die Unreife bedingte Komplikationen wie NEC oder fokale intestinale Perforationen auf, welche eine enterale Cholinzufuhr weiterhin erschwerten, oder sogar durch septische Komplikationen zusätzlich eine Verminderung der parenteralen Fettzufuhr mit nachfolgender Verminderung der parenteralen Cholinzufuhr bewirkten. Für die Untersuchung eines möglichen Zusammenhangs zwischen der postnatalen Cholinzufuhr und den kognitiven Leistungen der Frühgeborenen wurden Daten herangezogen, die im korrigierten Alter von durchschnittlich 22,3 Monaten im Rahmen einer neuropädiatrischen Routine-Untersuchung mithilfe der Bayley Scales of Infant and Toddler Development (Second Edition, BSID-II) im Sozialpädiatrischen Zentrum der Universitätskinderklinik Tübingen erhoben worden waren. Dabei erzielten jene 48 der ursprünglich 93 Kinder (Dropout-Rate 45%), für die zuverlässige Daten vorlagen, mit einem mittleren mentalen Entwicklungsindex (MDI) des BSID-II von 95,5 (± 11,9) einen leicht unterdurchschnittlichen Wert. Obwohl Cholin bei Tier und Mensch essentiell für die neurokognitive Entwicklung ist, konnte in unserer kleinen Studie kein statistisch signifikanter Zusammenhang zwischen der Cholinzufuhr und den kognitiven Leistungen der Frühgeborenen im BSID-II im Alter von knapp 2 Jahren nachgewiesen werden. Dies lag vermutlich an der geringen Fallzahl (N=48). Außerdem wurde eine adäquate Cholinzufuhr nur bei einem so geringen Teil der Patienten erreicht, dass die Frage, ob Kinder mit einer adäquaten Cholinzufuhr eine bessere kognitive Entwicklung zeigen, in dieser Studie nicht beantwortet werden kann. Es sind folglich in der Zukunft weitere prospektive Studien mit ausreichender Fallzahl notwendig, um die optimale Versorgung von Frühgeborenen mit Cholin und deren mögliche Auswirkung auf die neurokognitive Entwicklung zu erforschen

In Situ Muscle Power Differs Without Varying In Vitro Mechanical Properties in Two Insect Leg Muscles Innervated by the Same Motor Neuron

The mechanical behavior of muscle during locomotion is often predicted by its anatomy, kinematics, activation pattern and contractile properties. The neuromuscular design of the cockroach leg provides a model system to examine these assumptions, because a single motor neuron innervates two extensor muscles operating at a single joint. Comparisons of the in situ measurements under in vivo running conditions of muscle 178 to a previously examined muscle (179) demonstrate that the same inputs (e.g. neural signal and kinematics) can result in different mechanical outputs. The same neural signal and kinematics, as determined during running, can result in different mechanical functions, even when the two anatomically similar muscles possess the same contraction kinetics, force-velocity properties and tetanic force-length properties. Although active shortening greatly depressed force under in vivo-like strain and stimulation conditions, force depression was similarly proportional to strain, similarly inversely proportional to stimulation level, and similarly independent of initial length and shortening velocity between the two muscles. Lastly, passive pre-stretch enhanced force similarly between the two muscles. The forces generated by the two muscles when stimulated with their in vivo pattern at lengths equal to or shorter than rest length differed, however. Overall, differences between the two muscles in their submaximal force-length relationships can account for up to 75% of the difference between the two muscles in peak force generated at short lengths observed during oscillatory contractions. Despite the fact that these muscles act at the same joint, are stimulated by the same motor neuron with an identical pattern, and possess many of the same in vitro mechanical properties, the mechanical outputs of two leg extensor muscles can be vastly different

Moderate Dehydration Decreases Locomotor Performance of the Ghost Crab, Ocypode quadrata

The effect of dehydration on the aerobic metabolism and endurance of sustained, terrestrial locomotion was determined for the ghost crab, Ocypode quadrata, The rate of evaporative water loss, measured as the percentage of decrease in body mass per hour, was influenced by ambient temperature (Tₐ), Increasing Tₐ from 24° C to 30° C (40%-50% relative humidity) increased the rate of water loss from 2.3% h­­­­ˉ¹ ± 0.2% h­­­­ˉ¹ to 3.6% h­­­­ˉ¹ ± 0.6% h­­­­ˉ¹. Crabs were divided into three treatment groups to determine the effect of dehydration on aerobic metabolism: hydrated control crabs, slowly dehydrated crabs, and rapidly dehydrated crabs. Hydrated control crabs lost only 1.2% of their initial body mass. Slowly dehydrated crabs were dehydrated by 3.6% of their initial body mass at a rate of 2.3% hˉ¹. Finally, rapidly dehydrated crabs were dehydrated by 3.6% of their initial body mass at a rate of 3.6% hˉ¹. The maximal rate of oxygen consumption (Vo_2max) determined during treadmill exercise was decreased by 30% for slowly dehydrated crabs and by 70% for rapidly dehydrated crabs, as compared to hydrated controls. The minimum cost of locomotion was independent of the dehydration state for hydrated and slowly dehydrated crabs but was 62% lower for rapidly dehydrated crabs. Endurance was correlated with the speed at which Vo_2max was attained (the maximum aerobic speed [MAS]). The MAS was highest for hydrated control crabs and was decreased by 32% for slowly dehydrated crabs and by 68% for rapidly dehydrated crabs. We conclude that moderate dehydration can substantially decrease the ghost crab\u27s capacity for sustained, terrestrial locomotion

Energy Absorption During Running by Leg Muscles in a Cockroach

Biologists have traditionally focused on a muscle\u27s ability to generate power. By determining muscle length, strain and activation pattern in the cockroach Blaberus discoidalis, we discovered leg extensor muscles that operate as active dampers that only absorb energy during running. Data from running animals were compared with measurements of force and power production of isolated muscles studied over a range of stimulus conditions and muscle length changes. We studied the trochanter-femoral extensor muscles 137 and 179, homologous leg muscles of the mesothoracic and metathoracic legs, respectively. Because each of these muscles is innervated by a single excitatory motor axon, the activation pattern of the muscle could be defined precisely. Work loop studies using sinusoidal strains at 8 Hz showed these trochanter-femoral extensor muscles to be quite capable actuators, able to generate a maximum of 19-25 W kg-1 (at 25ºC). The optimal conditions for power output were four stimuli per cycle (interstimulus interval 11 ms), a strain of approximately 4%, and a stimulation phase such that the onset of the stimulus burst came approximately half-way through the lengthening phase of the cycle. High-speed video analysis indicated that the actual muscle strain during running was 12% in the mesothoracic muscles and 16% in the metathoracic ones. Myographic recordings during running showed on average 3-4 muscle action potentials per cycle, with the timing of the action potentials such that the burst usually began shortly after the onset of shortening. Imposing upon the muscle in vitro the strain, stimulus number and stimulus phase characteristic of running generated work loops in which energy was absorbed (-25 W kg-1) rather than produced. Simulations exploring a wide parameter space revealed that the dominant parameter that determines function during running is the magnitude of strain. Strains required for the maximum power output by the trochanter-femoral extensor muscles simply do not occur during constant, average-speed running. Joint angle ranges of the coxa-trochanter-femur joint during running were 3-4 times greater than the changes necessary to produce maximum power output. None of the simulated patterns of stimulation or phase resulted in power production when strain magnitude was greater than 5%. The trochanter-femoral extensor muscles 137/179 of a cockroach running at its preferred speed of 20 cm s-1 do not operate under conditions which maximize either power output or efficiency. In vitro measurements, however, demonstrate that these muscles absorb energy, probably to provide control of leg flexion and to aid in its reversal

Flexoelectricity and Ferroelectric Domain Wall Structures: Phase-Field Modeling and DFT Calculations

We show that flexoelectric effect is responsible for the non-Ising character of a 180° ferroelectric domain wall. The wall, long considered being of Ising type, contains both Bloch- and Néel-type polarization components. Using the example of classic ferroelectric BaTiO3, and by incorporating the flexoelectric effect into a phase-field model, it is demonstrated that the flexoelectric effect arising from stress inhomogeneity around the domain wall leads to the additional Bloch and Néel polarization components. The magnitudes of these additional components are two or three magnitudes smaller than the Ising component, and they are determined by the competing depolarization and flexoelectric fields. Our results from phase-field model are consistent with the atomistic scale calculations. The results prove the critical role of flexoelectricity in defining the internal structure of ferroelectric domain walls

Conductivity of Twin-Domain-Wall/Surface Junctions in Ferroelastics: Interplay of Deformation Potential, Octahedral Rotations, Improper Ferroelectricity, and Flexoelectric Coupling

Electronic and structural phenomena at the twin-domain-wall/surface junctions in the ferroelastic materials are analyzed. Carriers accumulation caused by the strain-induced band structure changes originated via the deformation potential mechanism, structural order parameter gradient, rotostriction, and flexoelectric coupling is explored. Approximate analytical results show that inhomogeneous elastic strains, which exist in the vicinity of the twin-domain-wall/surface junctions due to the rotostriction coupling, decrease the local band gap via the deformation potential and flexoelectric coupling mechanisms. This is the direct mechanism of the twin-wall static conductivity in ferroelastics and, by extension, in multiferroics and ferroelectrics. On the other hand, flexoelectric and rotostriction coupling leads to the appearance of the improper polarization and electric fields proportional to the structural order parameter gradient in the vicinity of the twin-domain-wall/surface junctions. The flexoroto fields leading to the carrier accumulation are considered as an indirect mechanism of the twin-wall conductivity. Comparison of the direct and indirect mechanisms illustrates a complex range of phenomena directly responsible for domain-wall static conductivity in materials with multiple order parameters

Low-Symmetry Monoclinic Ferroelectric Phase Stabilized by Oxygen Octahedra Rotations in Strained EuₓSr₁₋ₓTiO₃ Thin Films

Using Landau-Ginzburg-Devonshire theory and phase-field modeling, we explore the complex interplay between a structural order parameter (oxygen octahedron rotation) and polarization in EuxSr1-xTiO3 thin films. Under a biaxially tensile strain, a low-symmetry monoclinic phase with in-plane ferroelectric polarization is found to be stabilized by antiferrodistortive oxygen octahedra tilts. The monoclinic phase is stable over a wide temperature range. It is characterized by a large number of energetically equivalent polar and structural twin domains. This work demonstrates the development of a spontaneous polarization and piezo- and pyroelectricity in a ferroelastic twin boundary arising from flexoelectric coupling and rotostriction

The impact of COVID-19 on nurses (ICON) survey : nurses' accounts of what would have helped to improve their working lives

Aims To use nurses' descriptions of what would have improved their working lives during the first peak of the COVID-19 pandemic in the UK. Design Analysis of free-text responses from a cross-sectional survey of the UK nursing and midwifery workforce. Methods Between 2 and 14 April 2020, 3299 nurses and midwives completed an online survey, as part of the ‘Impact of COVID-19 on Nurses’ (ICON) study. 2205 (67%) gave answers to a question asking for the top three things that the government or their employer could do to improve their working lives. Each participants' response was coded using thematic and content analysis. Multiple response analysis quantified the frequency of different issues and themes and examined variation by employer. Results Most (77%) were employed by the National Health Service (77%) and worked at staff or senior staff nurse levels (55%). 5938 codable responses were generated. Personal protective equipment/staff safety (60.0%), support to workforce (28.6%) and better communication (21.9%) were the most cited themes. Within ‘personal protective equipment’, responses focussed most on available supply. Only 2.8% stated that nothing further could be done. Patterns were similar in both NHS and non-NHS settings. Conclusions The analysis provided valuable insight into key changes required to improve the work lives of nurses during a pandemic. Urgent improvements in provision and quality of personal protective equipment were needed for the safety of both workforce and patients. Impact Failure to meet nurses needs to be safe at work appears to have damaged morale in this vital workforce. We identified key strategies that, if implemented by the Government and employers, could have improved the working lives of the nursing and midwifery workforce during the early stages of the COVID-19 pandemic and could prevent the pandemic from having a longer-term negative impact on the retention of this vital workforce. Patient or Public Contribution No Patient or Public Contribution, due to the COVID-19 Pandemic, urgency of the work and the target population being health and social care staff