bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of the Scaphognathite Ventilatory Pump in the Shore Crab Carcinus Maenas II. Pumping Efficiency and Metabolic Cost
Authors: Wilkens J. L. , Wilkes P. R. H. , Evans J. 
Published: April 2021

ABSTRACT
The water pumping efficiency and the metabolic costs of the scaphog-nathites (SC), the gill ventilating water pumps, of shore crabs have been measured. The ratio of dynamic stroke volume to static pumping chamber volume, measured over the range of ventilation frequencies (fr) of 60−300 beats min-1, shows the water pumping efficiency to be 85%. Despite this high efficiency, the pump appears to become leaky at low FR. Reflux of water back through the pumping chamber was demonstrated by artificially increasing the pressure gradient across the SC chamber at normal fR.
The oxygen requirements of actively beating SCs, the ventilatory fraction of total metabolism, was measured by comparing oxygen consumption before and after SC ablation. The cost of ventilation for resting crabs is 30% of total . The oxygen requirement for a single SC beat is 0·032μmolO2 kg-1. The high ventilatory fraction of total may be one factor contributing to the low metabolic scope of most crustaceans.
Analysis Of The Scaphognathite Ventilatory Pump in the Shore Crab Carcinus Maenas III. Neuromuscular Mechanisms
Authors: Mercier A. Joffre , Wilkens Jerrel L. 
Published: April 2021

ABSTRACT
The motor output pattern to one of the ventilatory muscles of the scaphognathite (SC) in the shore crab, Carcinus rnaenas, was analysed from extracellular nerve recordings. During ‘forward mode’ bursting, an increase in the burst rate of L2b motor neurones is accompanied by an increase in the average intraburst firing frequency. The number of action potentials per burst, although variable, does not change consistently as a function of burst rate.
The influence of individual aspects of the motor pattern on isotonic contractions of muscle L2b was examined. Increasing the intraburst frequency leads to greater contraction and work output, and allows the muscle to lift heavier loads. This effect is correlated with an increase in the level of postsynaptic depolarization, due, at least in part, to greater summation of EPSPs. Increasing the burst rate alone also enhances muscle contraction and work, and results in greater depolarization. This latter effect appears to involve an accumulation of short-term facilitation, which becomes more acute as the time interval between the bursts is progressively shortened. In addition, contraction and depolarization are augmented by increasing the number of impulses per burst or the number of axons recruited.
These observations indicate some aspects of the motor output pattern which are appropriately modified to accommodate the changes in force and work demands which accompany a change in gill ventilation rate.
Matching of muscle properties and motoneurone firing patterns during early stages of development
Authors: Vrbová G. , Navarrete R. , Lowrie M. 
Published: April 2021

ABSTRACT
In adults, muscle fibres match the functional requirements of the motoneurone that supplies them. During early stages of postnatal development of the rat neither muscle fibre properties, nor activity patterns of motoneurones supplying fast and slow muscles have completed their differentiation. Nevertheless, even at this early stage of development the muscles have characteristic properties that are well matched to the activity patterns of immature motoneurones. With further development differentiation of motoneurone activity and muscle fibre properties goes hand in hand. If during this period of linked differentiation, connections between the motoneurones and muscle fibres are disrupted, the development of fast muscles is permanently impaired.
Motoneurone task groups: coping with kinematic heterogeneity
Authors: Loeb G. E. 
Published: April 2021

ABSTRACT
Physiological principles of motor control have generally been based on linear servocontrol theories in which transducers of force, length and velocity are used to provide feedback to the motor actuators. Within the past few years, recordings of the activity of motoneurones and proprioceptors during normal motor behaviour have indicated a diversity that is not consistent with any one theory of motor control. This paper examines the heterogeneity of kinematic conditions under which muscles are called on to perform, and attempts to correlate this with the effects of various fusimotor states on the activity of the muscle spindle afferents, the major sensory signal source in most feedback control schemes. The concept of ‘task groups’ is proposed, in which functional groups of alpha and gamma motoneurones and spindle afferents are programmed to achieve optimal control over relatively restricted but more linear parts of their operating curves. Such a functional compartmentalization of the motor apparatus is thus consistent with several different theories of servocontrol, although it remains unclear whether such conceptual mechanisms are actually embodied in the highly complex neural circuitry present in the spinal cord and higher motor centres.
Fuels and pathways as designed systems for support of muscle work
Authors: Hochachka P. W. 
Published: April 2021

ABSTRACT
Muscle in all animals relies upon four potential sources of energy: ATP hydrolysis, phosphagen hydrolysis, fermentations or oxidative metabolism. Although the relative contributions of different fuels varies greatly in different organisms, in none is there a simple reliance on stored ATP. Muscle work therefore requires a balance between rates of utilization and formation of ATP, a provision supplied by one of the three remaining fuels and metabolic pathways. Useful endogenous fuels must be storable at high level, and rapidly mobilizable with minimal perturbation of [ATP] and with minimal end-product effects on pH, charge or osmotic balance. In addition to displaying these properties, good exogenous fuels must be transferable at high rates between depot sites and muscle; actual flux rates of exogenous fuels depend upon respective ATP yields and are lowest for fuels which most amplify the yield of ATP per mol substrate oxidized. Subtrate flux rates must be matched with O2 flux rates and with rates of endogenous substrate mobilization in order that the right energy-yielding pathways are activated at the right times. Of various control possibilities, an effective competition for ADP (and possibly Pi) seems at this time to be the dominant strategy for assuring integration of aerobic and anaerobic ATP-yielding pathways.
Metabolic indicators of fibre recruitment in mammalian muscles during locomotion
Authors: Armstrong R. B. , Laughlin M. H. 
Published: April 2021

ABSTRACT
Fast-twitch-oxidative-glycolytic (FOG), fast-twitch-glycolytic (FG) and slow-twitch-oxidative (SO) fibres are distributed within and among physiological extensor muscles in mammals in predictable patterns. Deep muscles and the deep portions of extensor muscles are primarily composed of SO and FOG fibres, and the more peripheral portions of the muscles have higher concentrations of FG fibres. During terrestrial locomotion, the fibres are recruited in this same general order from postural standing through high speed running to jumping (i.e. during standing deep SO fibres are active and during locomotion there is a progressive peripheral recruitment of fibres from SO to FOG to FG). Several metabolic indicators may be used to map these fibre recruitment patterns, including glycogen loss in fibres, metabolic enzyme changes during training at different speeds, and distribution of blood flow within and among the muscles. Concerning the latter, during standing in rats blood flows in the hindlimb muscles are directly proportional to the SO fibre populations in the muscles. However, during locomotion the elevations in blood flow over pre-exercise are a function of the populations of FOG fibres in the muscles. Blood flows in the peripheral white portions (FG fibres) of extensor muscles are not significantly elevated until the rats run at high speeds, when the FG fibres presumably are recruited. During swimming, when flexor muscles are relatively more active than extensor muscles (as compared with terrestrial locomotion), blood flows in the flexors are correspondingly higher. Thus, there exists a clear ‘biological economy’ in the matching of blood flow to the specific fibres that are active within and among muscles during exercise.
The maximum forces exerted by animals
Authors: Alexander R. M. 
Published: April 2021

ABSTRACT
This paper reviews the maximum forces exerted by animals in a wide range of activities including running, jumping, swimming and biting. Most of the data refer to vertebrates and arthropods, ranging in size from 0·5-mg fleas to 3-tonne elephants. Maximum forces exerted on the environment give values of (force/body weight) which lie, in most cases, between 0-5 body mass−1/3 (kg) and 20 body mass−1/3. Maximum forces exerted by major muscle groups give values of (force/body weight) in most cases between 10 body mass− /3 and 50 body mass−1/3.
Sustained force development: specializations and variation among the vertebrates
Authors: Johnston I. A. 
Published: April 2021

ABSTRACT
The kinds of muscle fibre that are recruited for sustained force production by different vertebrates are described. Although aerobic metabolism always accounts for a significant proportion of their ATP turnover, no single characteristic such as colour, number and form of motor endplates, membrane properties, myosin isotype or contraction speed is diagnostic of such muscles. As mechanical power output increases, there is a tendency for a decrease in fatigue resistance with repetitive usage and an increase in both aerobic capacity and the fraction of energy requirements derived from glycolysis.
The role of compliance in mammalian running gaits
Authors: McMahon T. A. 
Published: April 2021

ABSTRACT
The running gaits used by both bipedal and quadrupedal animals are reviewed and contrasted. At high speeds, bipeds use both ordinary running, in which the legs move opposite one another, and hopping. Quadrupeds generally use the trot or its variations at moderate speeds, and first the canter and then the gallop as speed increases. Running in both bipeds and quadrupeds generally involves at least one aerial phase per stride cycle, but certain perturbations to running including running in circles, running under enhanced gravity, running on compliant surfaces and running with increased knee flexion (Groucho running) can reduce the aerial phase, even to zero.
A conceptual model of running based on the idea that an animal rebounds from the ground like a resonant mass-spring system may be used to compare the various gaits. The model makes specific predictions which show that galloping is generally faster than cantering, pronking or trotting, and requires lower peak vertical forces on the legs while also giving a smoother ride. Even so, trotting might be preferred to galloping at low and moderate speeds for the same reason that normal running is preferred to Groucho running - the more compliant gait offers a smoother ride and lower vertical ground-reaction forces on the feet, but this can only be obtained at a high cost of increased metabolic power.
Properties of the muscle proteins - a comparative approach
Authors: Perry S. V. 
Published: April 2021

ABSTRACT
One of the striking features of muscle systems is the wide range in properties they exhibit. This adaptability of muscle to its physiological role is a consequence of the specialization that occurs by the normal process of development and the ability to adapt further to the functional demands when the normal developmental changes are assumed to be complete - a property often referred to as plasticity.
Malleability of the motor system: a comparative approach
Authors: Goldspink G. 
Published: April 2021

ABSTRACT
The various ways in which the power output of muscles can be changed are described. As a result of exercise and growth, force production is increased by an increase in the cross-sectional area of the fibres. This is associated with changes in the rate of synthesis and degradation of muscle proteins which lead to build up of the myofibrils. These then split longitudinally when they reach a critical size. This process is repeated so that the number of myofibrils increases very considerably. Also, during growth, the displacement is increased by increasing the length of the muscles. To do this more sarcomeres are produced in series along the length of the fibres. This is induced by stretch which also encourages fibre growth in girth as well as in length. Yet another way of changing the power output of a muscle is to change the types of muscle fibres (motor units) within the muscle. Fibre type transformation has been shown to occur with cross innervation and stimulation but it does not usually occur with exercise training. It has been possible, however, to change the fibre type proportions in young animals. Also, by combining stretch with stimulation, it has been possible for instance to make the fast glycolytic fibres add on fast oxidative type sarcomeres or even slow oxidation type sarcomeres. Interestingly, fibre transformation also occurs in some species of fish during acclimation to low temperatures in that the specific myofibrillar ATPase activity is increased. This means that the reduction in power output due to decreased temperature is to some extent compensated for by an increase in the intrinsic rate of shortening. EMG studies of fish swimming at different temperatures have shown that the acclimated fish can swim faster and can derive more aerobic sustainable power as a result of this change.
Myosin isoenzymes as molecular markers for muscle physiology
Authors: Whalen R. G. 
Published: April 2021

ABSTRACT
Myosin is a major component of skeletal muscle and it plays a central role in determining the physiological performance of adult tissue. Developing muscles contain myosin molecules which are different from the adult forms, and these isoenzymes have been found to be characteristic markers of the diverse physiological and pathological states of muscle tissue. The differences between these isoenzymes may be demonstrated by protein chemical, immunochemical and genetic evidence. The study of the sequential transitions between isoenzymes represents a means for characterizing the dynamic nature of muscle development, and neuronal and hormonal influences have been identified which contribute to the regulation of these transitions. The perspectives for future work include genetic studies, elucidation of the pathways relating extracellular signals to changes in gene expression, and the possibility that studies of myosin isoenzymes might further understanding of muscle pathology.
From sarcomeres to whole muscles
Authors: Morgan D. L. 
Published: April 2021

ABSTRACT
The series connection of sarcomeres in a muscle raises the possibility of instabilities due to some sarcomeres being capable of greater isometric tension than others, due to non-uniform activation, cross-sectional area or sarcomere length. Such instabilities are heavily damped by the force-velocity curve and stabilized by passive tension. The variation of active tension with sarcomere length may act to stabilize or destabilize the situation. Such instabilities can affect tension in a complex manner, causing both increases and decreases in different situations. Some examples of situations where sarcomere non-uniformities have been observed or inferred are given, and their mode of action explained.
Excitation-contraction coupling: the link between the surface and the interior of a muscle cell
Authors: Peachey L. D. 
Published: April 2021

ABSTRACT
The full contractile tension of a skeletal muscle fibre typically is developed a few tens to a few hundreds of milliseconds after the upstroke of the surface action potential. This generally is an insufficient time for an activator, such as calcium ion, to diffuse from the surface to the centre of the fibre (Hill, 1948, 1949). Yet we know that the centre of the fibre is activated, even in a single twitch (Gonzalez-Serratos, 1971). Measurements of the quantity of calcium entry through the surface membrane per contraction (Bianchi & Shanes, 1959) give values that are at least an order of magnitude smaller than the amount of calcium thought to be needed for full activation of contraction. Additionally, more recent evidence indicates that this calcium entry through the surface occurs too late to be directly involved in contraction activation (Sanchez & Stefani, 1978). All these results argue against a mechanism for coupling electrical activity at the surface of the fibre to contraction of the interior (E-C coupling) that depends on entry and diffusion of calcium ions from the surface to the contractile fibrils.
Ventilation, Circulation and Their Interactions in the Land Crab, Cardisoma Guanhumi
Authors: Burggren Warren , Pinder Alan , Mcmahon Brian , Wheatly Michele , Doyle Michael 
Published: April 2021

ABSTRACT
Physiological variables for ventilation (scaphognathite frequency, branchial chamber pressure and branchial air flow) and for circulation (heart rate, intracardiac and pericardial haemolymph pressure) were measured in the land crab Cardisoma guanhumi (Latreille). Crabs were studied both in air alone and in air with access to a shallow layer of fresh, brackish or sea water.
During complete air exposure, forward scaphognathite beating predominated and reversed scaphognathite beating was very infrequent. Periods of apnoea were rare. When crabs were able to immerse the Milne-Edwards openings to the branchial chambers in water, scaphognathite reversal occurred much more frequently, and most air flow through the branchial chambers was generated by this mode of ventilation. Changes in water salinity had no effect on respiratory patterns. The cyclic variation between forward and reversed scaphognathite beating appears to serve not only to ventilate the branchial chambers with air, but also to flush water through the branchial chambers for non-respiratory purposes such as ion, water and acid-base regulation.
Haemolymph pressures were comparatively low (14 mmHg systolic, 6mmHg diastolic). During diastole a pressure gradient of approximately 0·6 mmHg existed between the pericardial space and the heart lumen. Pauses in heart beat were never observed. Circulatory events were closely coordinated with adjustments in ventilation. Reversed scaphognathite beating produced a transient increase in systolic and diastolic haemolymph pressure due to the rise in branchial air pressure acting directly upon the large, haemolymph-filled spaces lining the branchial chambers. A transient bradycardia accompanied this brief rise in central haemolymph pressures. Possible mechanisms for the regulation of haemolymph pressure are discussed.
A Passive Two Layer Permeability-Water Content Model for Periplaneta Cuticle
Authors: Machin J. , Lampert G. J. 
Published: April 2021

ABSTRACT
Two layers in Periplaneta pronotum, endocuticle and combined epicuticle and exocuticle were functionally distinguished by their permeabilities and water affinities. A passive model combining the permeabilities of these layers and the water content of the endocuticle was designed to predict pronotal water contents in a variety of ambient activities at 20 °C.
The model predicted cuticle water contents with acceptable accuracy above ambient activities of 0·56 but overestimated them in drier conditions. Despite universally high water activities in the endocuticle, differences in water content related to ambient activity were predicted. Cuticle water contents below haemolymph equilibrated values, represented in the literature as evidence of active water regulation, were largely attributed to passive activity gradients combined with evaporation errors.
The Mechanism of Tubocurarine Action on Mechanoreceptor Channels in the Protozoan Stentor Coeruleus
Authors: Wood David C. 
Published: April 2021

ABSTRACT
(+)-Tubocurarine (TC) decreases the probability that the protozoan, Stentor coeruleus Ehrenberg, will contract in response to mechanical stimulation, because it selectively depresses mechanoreceptor currents. Resting membrane properties and action potentials are not significantly altered by the drug.
Stentor incubated in media containing radioactively labelled TC (TC*) retain TC* after extensive washing despite a rather high apparent KD (19·7μmol 1-1). The incubation curve for TC* binding exhibits an initial exponential rise followed by a linear increase. Wash-out of bound TC* and elimination of the exponential component of the incubation curve is observed if the TC* incubation is followed by a 5-s exposure to 8% urea; therefore, the exponential component represents a reversible binding process. TC* binding in the exponential component is highly correlated (r &lt; — 0·96) with the depression in receptor current and response probability when incubation time, drug concentration and drug (gallamine, TC, decamothonium and succinylcholine) are varied. These correlations suggest that the exponential binding is to functional mechanoreceptors.
Mechanoreceptor currents are decreased by hyperpolarization and increased by depolarization, indicating that the mechanoreceptor channel is voltage-dependent. At hyperpolarized potentials the channels are in a form (the U form) which cannot be opened by mechanical stimulation; at depolarized potentials they are in a form (the R form) which can be opened. TC appears to bind to the U form with higher affinity than to the R form, since depolarization reduces the amount of bound TC* and relieves the depression of mechanoreceptor current produced by TC.
Myocardial Oxygen Consumption in the Sea Raven, Hemitripterus Americanus : The Effects of Volume Loading, Pressure Loading and Progressive Hypoxia
Authors: Farrell A. P. , Wood S. , Hart T. , Driedzic W. R. 
Published: April 2021

ABSTRACT
Myocardial oxygen consumption was measured using an in situ, perfused heart preparation at 10°C increased in a linear fashion with power output when cardiac output was elevated (volume loading). The increased was possible through improved O2 delivery , but was reduced. The mechanical efficiency of the heart was improved. also increased in a linear fashion with power output when output pressure was increased with constant (pressure loading). The increased was supported by increased O2 removal from the perfusate since oxygen delivery was constant. Once more, improved mechanical efficiency was observed. decreased as O2 delivery was reduced with progressive hypoxia. Even so, power output was maintained at a perfusate input of 81 Torr. Five of 11 hearts survived a 30-Torr exposure, but with a 29 % decrease in power output and a 5-fold reduction in . The increase in the apparent aerobic efficiency which enabled this is discussed.
The Neural Basis of Escape Swimming Behaviour in the Squat Lobster Galathea Strigosa
Authors: Sillar Keith T. , Heitler William J. 
Published: April 2021

ABSTRACT
A motor programme underlying backward swimming in the squat lobster Galathea strigosa is described. Swimming is accomplished by repeated flexions and extensions of the abdomen. This investigation indicates that the behaviour is generated centrally, possibly in the suboesophageal or thoracic nervous system, and is probably homologous with non-giant escape behaviour in crayfish. The effects of sensory feedback on the swimming rhythm have been investigated in free-swimming and restrained preparations. Proprioceptive feedback, probably originating in the abdominal muscle receptor organs, is involved in the maintenance of high frequency swimming. During swimming, the walking legs and unmodified male swimmerets are rhythmically active in phase with abdominal flexion. Swimmeret ‘flicking’ in the male is effected by high frequency spiking in a single phasic swimmeret motor neurone. The results suggest that, when active, the central pattern generator for swimming dominates other neural oscillators for rhythmic limb movements.