bluuebunny/crossref_metadata_2025 huggingface dataset:
Brain Oscillator(s) Underlying Rhythmic Cerebral And Buccal Motor Output In The Mollusc,Pleurobranchae Calieornica
Authors: Davis W. J. , Kovac Mark P. , Croll Roger P. , Matera Eugene M.
Published: April 2021

Tonic (d.c.) intracellular depolarization of the previously identified phasic paracerebral feeding command interneurones (PCps) in the brain of the carnivorous gastropod Pleurobranchaea causes oscillatory neural activity in the brain, both before and after transecting the cerebrobuccal connectives. Therefore, cycle-by-cycle ascending input from the buccal ganglion is not essential to cyclic brain activity. Instead the brain contains an independent neural oscillator(s), in addition to the oscillator(s) demonstrated previously in the buccal ganglion (Davis et al. 1973). Transection of the cerebrobuccal connectives immediately reduces the previously demonstrated (Kovac, Davis, Matera & Croll, 1983) long-latency polysynaptic excitation of the PCps by the polysynaptic excitors (PSEs) of the PCps. Therefore polysynaptic excitation of the PCps by the PSEs is mediated by an ascending neurone(s) from the buccal ganglion. The capacity of feeding command interneurones to induce neural oscillation in the isolated brain declines to near zero within 1 h after transection of the cerebrobuccal connectives, suggesting that this capacity is normally maintained by ascending information from the buccal ganglion. The results show that this motor system conforms to a widely applicable general model of the neural control of rhythmic behaviour, by which independent neural oscillators distributed widely in the central nervous system are coupled together to produce coordinated movement.
Mechanics, Power Output and Efficiency of the Swimming Muskrat (Ondatra Zibethicus)
Authors: Fish F. E.
Published: April 2021

The surface swimming of muskrats (Ondatra zibethicus Linnaeus) was studied by forcing individual animals to swim against a constant water current, of velocity ranging from 0·2 to 0·75 ms−1, in a recirculating water channel. Lateral and ventral views of the swimming muskrats were filmed simultaneously for analysis of thrust by the propulsive appendages.

Drag measurements and flow visualization on dead muskrats demonstrated that these animals experience large resistive forces due to the formation of waves and a turbulent wake, because of the pressure and gravitational components which dominate the drag force.

Biomechanical analysis demonstrated that thrust is mainly generated by alternating strokes of the hindfeet in the paddling mode. A general lengthening of the hindfeet and presence of lateral fringe hairs on each digit increase the surface area of the foot to produce thrust more effectively during the power phase of the stroke cycle. Increased energy loss from drag on the foot during the recovery phase is minimized by configural and temporal changes of the hindfoot. Employing the models developed by Blake (1979, 1980a,b) for paddle propulsion, it was found that as the arc through which the hindfeet were swept increased with increasing velocity the computed thrust power increased correspondingly. However, the frequency of the stroke cycle remained relatively constant across all velocities at a level of 2·5 Hz.

Both mechanical and aerobic efficiencies rose to a maximum with increasing swimming velocity. The aerobic efficiency, which examined the transformation of metabolic power input to thrust power output reached a value of 0·046 at 0·75 ms−1. The mechanical efficiency expressing the relationship of the thrust power generated by the paddling hindfeet and laterally compressed tail (Fish, 1982a,b) to the total mechanical power developed by the propulsive appendages increased to a maximum of 0·33 at 0·75 ms−1.

I conclude that the paddling mode of swimming in the muskrat is relatively inefficient when compared to swimming modes which maintain a nearly continuous thrust force over the entire propulsive cycle. However, the paddling mode permits the muskrat to generate propulsive forces effectively while swimming at the surface. The evolution of this mode for semi-aquatic mammals represents only a slight modification from a terrestrial type of locomotion.
Development of Swimming Movements and Musculature of Larval Herring (Clupea Harengus)
Authors: Batty R. S.
Published: April 2021

A kinematic analysis was made of swimming of larval herring Clupea harengus L. Swimming style was found to change with growth and development; the amplitude of swimming movements of early post-yolk-sac larvae increases linearly towards the tail, a style of swimming which relies mainly on resistive forces for propulsion. Later, after the caudal and dorsal fins have developed, the swimming style changes, in response to an increase in Reynold’s Number, such that inertial forces are more important. In this type of swimming the amplitude increases more rapidly than linearly towards the tail.

The distribution of red and white muscle fibre types was studied in relation to development. On hatching, red muscle fibres were found to be arranged as a single layer on the outside of the myotomes. They develop into the adult distribution, concentrated at the midline of the flank near the skin, only after the gills and circulation become fully functional.
Lability of Blood Volume in Snakes and its Relation to Activity and Hypertension
Authors: Lillywhite Harvey B. , Smits Allan W.
Published: April 2021

The lability of blood volume and its relationship to locomotor activity was investigated in two species of snakes Elaphe obsoleta, Say and Crotalus viridis, Rafinesque. Repetitive measurements of blood volume, determined from changes in the specific activity of circulating 51Cr-labelled erythrocytes, indicated that 15 min of locomotor activity reduced blood volume by 21 % due to filtration of plasma from capillaries. This magnitude of plasma translocation exceeds that measured in exercising mammals by factors of 2 to 7, depending on the intensity and duration of muscular activity. Activity produced changes in arterial blood pressure, heart rate and haematocrit that were proportionately similar in both species, increasing approximately 57, 85 and 25 %, respectively, above resting values. Arterial infusion of norepinephrine increased arterial pressure by more than 100 % and reduced blood volumes 8·6 and 17·0% in Elaphe and Crotalus, respectively. These data demonstrate that blood volume varies substantially in relation to activity or the hypertensive state of these reptiles. Thus care must be employed in interpreting or comparing reported measurements of blood volume in these and probably other vertebrates.
Functional Conflicts Between Feeding and Gas Exchange in Suspension-Feeding Tadpoles, Xenopus Laevis
Authors: Feder Martin E. , Seale Dianne B. , Boraas Martin E. , Wassersug Richard J. , Gibbs Allen G.
Published: April 2021

Air-breathing tadpoles of Xenopus laevis (Amphibia: Anura) use buccopharyngeal surfaces for both gas exchange and capture of food particles in the water. In dense food suspensions, tadpoles decrease ventilation of the buccopharynx and increase air breathing. The lung ventilatory frequency is elevated even though the rate of oxygen consumption is at or below resting levels, suggesting that the lung hyperventilation reflects compensation for decreased buccopharyngeal respiration rather than an increased metabolic requirement. If tadpoles in hypoxic water are prevented from breathing air, they increase buccopharyngeal respiration at the expense of feeding. Aerial respiration evidently permits the buccopharyngeal surfaces to be used primarily for food entrapment.
Mechanical Properties and Control of Nonmuscular Catch in Spine Ligaments of the Sea Urchin, Strongylocentrotus Franciscanus
Authors: Diab Mohammad , Gilly WM. F.
Published: April 2021

Catch was induced in the spine ligaments of Strongylocentrotus franciscanus (Agassiz) (surrounding muscle and nervous tissue removed) by mechanical agitation. When the catch mechanism is set, the tensile stiffness of urchin ligament can change by nearly an order of magnitude and approaches that of vertebrate tendon. Deflection of a spine in catch through an angle of more than 10° damages the catch mechanism. Setting of catch depends on extracellular calcium. Transglutaminase inhibitors (cadaverine and putrescine) prevent the setting of catch. A model involving Ca-dependent activation of a transglutaminase-like enzyme is discussed as a possible basis for the setting of catch by crosslinking collagen fibrils.
Power output and force-velocity relationship of red and white muscle fibres from the Pacific blue marlin (Makaira nigricans)
Authors: Johnston I. A. , Salamonski J.
Published: April 2021

Single white fibres and small bundles (two to three) of red fibres were isolated from the trunk muscle of Pacific Blue Marlin (50-121 kg body weight). Fibres were chemically skinned with 1 % Brij. Maximum Ca2+-activated force production (Po) was 57 kN m−2 for red fibres and 176 kN m−2 for white fibres at 25 °C. The force-velocity (P-V) characteristics of these fibres were determined at 15 and 25 °C. Points below 0·6 Po on the P-V curve could be fitted to a linear form of Hill’s equation. The degree of curvature of the P-V curve was similar at 15 and 25 °C (Hill’s constant a/P0 = 0·24 and 0·12 for red and white fibres respectively). Extrapolated maximum contraction velocities (Vmax) were 2·5 muscle lengths s−1 (LOS−1) (red fibres) and 5·3 Los−1 (white fibres) at 25 °C. Q10(15-25°C) values for Vmax were 1·4 and 1·3 for red and white fibres respectively. Maximum power output had a similar low temperature dependence and amounted to 13Wkg−1 for red and 57Wkg’ for white muscle at 25 °C. The results are briefly discussed in relation to the locomotion and ecology of marlin.
Differences in temperature dependence of muscle contractile properties and myofibrillar ATPase activity in a cold-temperature fish
Authors: Johnston I. A. , Sidell B. D.
Published: April 2021

Single muscle fibres were isolated from the fast myotomal muscle of the teleost Myoxocephalus scorpius L. and chemically skinned with 1 % Brij. Maximum Ca2+-activated force (Po) increased from 14·5 ± 1·1 N cm-2 at 2°C to 19·1 ± 1·8 N cm-2 at 15 °C (mean ± S.E.). Maximum contraction velocity was determined by Hill’s slack-test method (V0) and by extrapolation from force-velocity (P-V) relationships (Vmax). There was a linear relation between log10 V0 and temperature below 15°C (Q10= 1·9, P<0·01). The force-velocity characteristics of the fibres were determined at 2 °C and 20°C. Points below 0·6 P0 on the P-V curve could be fitted by a linear form of Hill’s equation. Extrapolated Vmax values were 0·55 muscle lengths s-1 (L0s-1) at 2°C and 1·54L0s-1 at 20°C. Curvature of the P-V relationship was independent of temperature. The Mg24-, Ca2+-ATPase activity of Triton-X 100 extracted myofibrils was determined under similar ionic conditions to those used in skinned fibre experiments. (Ionic strength 0·16 mmol1-1, pMgATP2·5). A linear relationship between log10 ATPase and temperature was only obtained below 15 °C {P< 0·001). Above 15 °C, the Q10 for ATPase decreased significantly. The Q10(0-15°C) for ATPase activity (3·9) was significantly higher than for unloaded contraction velocity. Supercontraction of isolated myofibrils to very short sarcomere lengths and differences in the mechanical constraints for crossbridge cycling between the preparations probably account for the lack of proportionality between these two parameters.
The Versatile Synapse
Authors: Pitman Robert M.
Published: April 2021

‘Typically’ chemical synaptic transmission takes place when an influx of calcium ions during a presynaptic nerve impulse triggers exocytosis of neurotransmitter substance from synaptic vesicles. The neurotransmitter diffuses across the synaptic cleft and occupies receptors embedded in the subsynaptic membrane. This interaction (directly or via a second messenger) operates characteristic ion channels and produces an increase in the postsynaptic membrane permeability to particular ions. Depending on the ionic species to which the postsynaptic membrane becomes more permeable, the physiological response will be an excitatory or an inhibitory postsynaptic potential. The action of neurotransmitters may be terminated either by enzymic inactivation or by cellular uptake mechanisms.

Over the last decade it has become clear that a neurotransmitter substance may exert a number of different actions on a single postsynaptic neurone. These may involve opening or closure of either voltage-independent or voltage-dependent ion channels. It is also possible that in some instances transmitters may act on neuronal biochemical systems to modify the physiology of postsynaptic cells without directly altering their electrical characteristics.

Analysis of the postsynaptic actions of neurotransmitter substances has become further complicated by the increasing body of evidence which indicates that more than one transmitter substance (one of which may be a peptide) can be released from a single presynaptic neurone. The significance of such dual transmitter systems has yet to be fully elucidated.

The efficacy of transmission across many synapses may be modified by either presynaptic or postsynaptic mechanisms ; both transmitter release and postsynaptic responsiveness may depend on the recent history of a single synapse, on synaptic inputs from other neurones or on circulating neuroactive substances.
The Pattern Of Osmotic Regulation In Larvae Of The Mosquito Culiseta Inornata
Authors: Garrett Margaret , Bradley Timothy J.
Published: April 2021

Larvae of Culiseta inornata (Williston) can survive and complete development in dilutions of sea water ranging from 50–700 mosmol kg-1. The larvae hyperregulate with regard to haemolymph osmotic concentration in dilute media (50–400 mosmol kg−1) and osmoconform when external salinities exceed 400 mosmol kg−1. This pattern of osmoregulation is distinct from that observed in freshwater and saline-water mosquito species. We propose that mosquitoes exhibiting this osmoregulatory pattern should be described as ‘brackish-water’ species. Larvae of Culiseta inornata are able closely to regulate both sodium and chloride ion concentrations in the haemolymph over the full range of salinities tested (50–750mosmolkg−1). The Malpighian tubules produce an isosmotic, potassium-rich fluid. In vitro and in vivo sampling of rectal fluids demonstrates that rectal secretions are isosmotic or only slightly hyperosmotic to the haemolymph and the surrounding saline media, and that they are isotonic with regard to sodium.
Pressure and Water Flow Patterns in the Respiratory Tract of the Bass (Micropterus Salmoides)
Authors: Lauder George V.
Published: April 2021

Instantaneous water velocities in the respiratory tract of bass, Micropterus salmoides (Lacepède), were measured using a fast-responding hot-film anemometer. The flow velocity waveform varied within the buccal cavity, with lower peak velocities at the back than at the front. Flow velocity in both the buccal and opercular cavities varied over the respiratory cycle, and 80 % of signal power in the velocity waveform was between 1 and 10 Hz. Flow within the buccal cavity reached a maximum velocity of 50cms−1 and did not decline to zero, even when differential pressure across the gills was negative. Simultaneous measurement of dimensional changes in the branchial apparatus, pressure and velocity fluctuations showed that gill bar adduction coincides both with the pressure reversal across the gills and with maximum flow velocities in the opercular cavity. The movement of the gill bars during respiration causes flow velocity fluctuation just in front of the primary lamellae and may be an important component of intraoral resistance contributing to the phase differences between pressure and velocity waveforms.
Interneuronal Network Acting on Snail Neurosecretory Neurones (Yellow Cells and Yellow-Green Cells of Lymnaea)
Authors: Benjamin P. R.
Published: April 2021

Neurosecretory cells in Lymnaea are the follower cells of a network of interneurones consisting of four different cell types, three of which are inhibitory and one excitatory. One identified interneurone, the visceral white interneurone (VWI), inhibits the Yellow Cells and Yellow-green Cells, or converts Yellow Cells from single spiking to doubletting or bursting. A second interneurone, RPeDl, has weak inhibitory effects on both types of neurosecretory cells but its main effect is to inhibit the VWI and allow the Yellow Cells to be strongly influenced by spontaneous EPSP inputs (input 3).
Pulmonary Mechanics and the Work of Breathing in the Lizard, Gekko Gecko
Authors: Milsom William K. , Vitalis Timothy Z.
Published: April 2021

Measurements of pulmonary mechanics made on anaesthetized specimens of the Tokay gecko Gekkogecko (Linné), indicate that both static and dynamic pulmonary mechanics are dominated by the mechanics of the body cavity and chest wall. The lungs are relatively large and compliant and offer little resistance to air flow at any of the ventilation frequencies (f) used in this study. The body wall is relatively stiff and becomes less compliant with increasing ventilation frequency and with increasing tidal volume (VT) at the higher frequencies. The vast majority of the work performed in breathing is used to overcome elastic forces in the chest wall resisting lung inflation. This work increases exponentially with increases in volume. As a consequence, in terms of total ventilation, the most economic breathing pattern is a high frequency, low tidal volume pattern in which changes in minute ventilation are most economically produced solely by changes in f. Because reductions in tidal volume drastically reduce alveolar ventilation volume while dead space remains constant, the same arguments do not apply to alveolar minute ventilation . In terms of alveolar minute ventilation, there is an optimum combination of f and VT for each level of VA, with changes in VA being most economically produced by almost equal changes in both f and VT.
Adrenergic Swelling of Nucleated Erythrocytes: Cellular Mechanisms in A Bird, Domestic Goose, and Two Teleosts, Striped Bass and Rainbow Trout
Authors: Nikinmaa Mikko , Huestis Wray H.
Published: April 2021

The mechanism of adrenergic swelling and associated pH changes was investigated in avian (goose) and teleost (striped bass and rainbow trout) erythrocytes.

The swelling of goose red cells was probably caused by Na+/K+/Cl− cotransport and consecutive osmotic flow of water into the cell. Goose red cells swelled when exposed to isoproterenol in the presence of elevated extracellular K+, but not at physiological K+ concentrations. The swelling was quantitatively inhibited by furosemide, and by removing Cl− from the incubation medium, but was not affected by DIDS.

The isoproterenol-induced swelling of fish erythrocytes may be due to loosely coupled Na+/H+ and Cl/HCO3− exchanges. Furosemide did not completely inhibit the swelling of striped bass red cells. The cell volume increased even if K+ was completely removed from the incubation medium. In contrast, both DIDS and amiloride treatment, and the removal of Na+ from the incubation medium, inhibited the volume changes. In fish red cells the swelling is associated with a clear acidification of the medium and alk-alinization of the red cell contents. This phenomenon was most pronounced when the cells were treated simultaneously with DIDS and isoproterenol; the intracellular pH became higher than the extracellular one. Both amiloride and removal of Na+ from the incubation medium prevented the reversal of the transmembrane pH gradient in cells treated simultaneously with DIDS and isoproterenol.
Magnetic Remanence in the Western Atlantic Spiny Lobster, Panulirus Argus
Authors: Lohmann Kenneth J.
Published: April 2021

The magnetic characteristics of 15 western Atlantic spiny lobsters (Panulirus argus) were analysed with a superconducting cryogenic magnetometer. Each specimen possessed a significant natural remanent magnetization (NRM) and isothermal remanent magnetization (IRM), indicating that ferromagnetic material is present. Analyses of the distribution of total remanence and mass-specific remanence indicate that magnetic material is concentrated in the cephalothorax, particularly in tissue associated with the fused thoracic ganglia. Mass-specific remanence and the total quantity of magnetic material in the cephalothorax and abdomen both increase as functions of carapace length.

The NRM is significantly orientated in at least four regions of the body. The NRM of the left half of the posterior cephalothorax is directed posteriorly, while that of the right half is orientated anteriorly. In addition, the NRM of the middle cephalothorax is orientated toward the right side of the animal; the NRM of the telson-uropods region is directed toward the left. The functional significance of these regions of orientated remanence is not known, but such a pattern could result from the ordered alignment of permanently magnetic particles comprising a magnetoreceptor system.
Hearing in Notodontid Moths: A Tympanic Organ with a Single Auditory Neurone
Authors: Surlykke Annemarie
Published: April 2021

Notodontid moths possess paired tympanic organs basically similar to the ears in other noctuoid families, but with a single auditoryA cell. The A cell and the non-auditory B cell were studied anatomically by infusion of C0CI2 and physiologically by recordings from the tympanic nerve. The response of the A cell is determined by intensity parameters and temporal parameters of an ultrasonic stimulus. The notodontid ear is as sensitive as the ears of sympatric noctuids. The directional sensitivity is approximately the same as in noctuids of comparable size (maximal interaural intensity difference of 10–15 dB). The dynamic range of the A cell is about 20–25 dB. Sound levels exceeding the threshold by 30–40dB will saturate the A cells in both ears. Stimuli with different pulse lengths (from 5 to 200 ms, corresponding to pulse repetition rates (PRR) from 100–2·5 Hz), but equal duty cycles (50%) gave a maximum response for pulse lengths lying between 30 and 50 ms. The receptor cell followed the sound pulses in a one-to-one manner even at a PRR of 200 Hz. Notodontid moths seem to show the same ‘bimodal’ evasive behaviour as noctuids. This behaviour can be explained on the basis of intensity parameters, since only low intensity stimuli will give the notodontid directional information. Hence, directional evasive behaviour is expected at low sound pressure levels (SPL), while high SPL (saturating both A cells) should elicit a non-directional evasive behaviour. However, the evasive behaviour could also be explained in terms of time parameters. Hunting bats increase the PRR of their cries when closing in on a prey and the moths may be able to use these time cues for changing their behaviour.
Muscle Function: A Personal View
Authors: Wilkie D. R.
Published: April 2021

We are far more likely to arrive at our destination if we know what it is. For those of us who are interested in how muscles work, the destination is the progressive unification of our knowledge of the physics, chemistry and structure - at all levels - of muscular systems. The same integration is needed to understand other organs, but in my opinion the field of muscle research has progressed further than the others. Optimists that we are, our goal seems almost within our grasp. Perhaps it is just at the rainbow’s end …
The size-principle: a deterministic output emerges from a set of probabilistic connections
Authors: Henneman E.
Published: April 2021

To understand how even a single muscle is controlled, we must understand how a large ensemble of neurones can generate a complex function through the collective action of its members. The orderly recruitment of motoneurones (MNs) and motor units according to their sizes or tensions (Henneman, 1957; Henneman, Somjen & Carpenter, 1965a,b) is the product of collective action, illustrating how hundreds of MNs operate as a functional entity to control a muscle. Fig. 1 reproduces the recruitment of motor units recorded from a rabbit’s diaphragm during a series of progressively stronger inspirations (G. Yasargil, unpublished). With each contraction larger spikes were recorded in orderly sequence, indicating the discharge of larger motor units. Nearly invariant recruitment orders have been recorded from the MNs or muscles of more than 20 species (Henneman & Mendell, 1981).
Control properties of motor units
Authors: De Luca C. J.
Published: April 2021

This review will deal with two evolving concepts which describe and attempt to unify various observations concerning the behaviour of motor units that have been reported during the past decade. The two concepts are: (1) The common drive which describes the behaviour of the firing rates of motor units, and appears to provide a simple schema for controlling motor units; and (2) the firing rate/recruitment interaction which appears to en-hance the smoothness of the force output of a muscle.

The evolution of these concepts has been expedited by the development of recent techniques such as our decomposition technique which enables us accurately to decompose the myoelectric signal into the constituent motor unit action potential trains. For details refer to LeFever & De Luca (1982), Mambrito & De Luca (1983) and Mambrito & De Luca (1984).
The Crossbridge Mechanism of Muscular Contraction and its Implications
Authors: Huxley H. E.
Published: April 2021

The basic features of the sliding-filament crossbridge mechanism are reviewed briefly, and some recent objections involving supposed changes in A-filament lengths are discussed. X-ray diffraction studies on live muscles show no sign of a decrease in axial spacing during contraction, and it is unlikely that a stepwise shortening or depolymerization of A-filaments would provide a plausible contraction mechanism. Thus electron microscope observations which occasionally are reported to show such length changes probably arise from experimental artefact, of which there are many sources.

The factors which govern tension and speed in muscle contraction are described. Since all vertebrate striated muscles which have been studied have A-bands of at least approximately the same length, they are likely to have rather similar maximum isometric tensions. The design probably matches this tension to the strength of the filaments themselves. The large variations in shortening speeds between different muscles and different animals arise because of corresponding variations in the rates of particular steps in the crossbridge cycle and in the rate of ATP splitting by the actin-myosin complex involved. Questions concerning the nature and the speed of the activation mechanism are also discussed.
Metabolic heterogeneity of muscle fibres
Authors: Pette D.
Published: April 2021

Mammalian skeletal muscle is an extremely heterogeneous tissue. Its diversity results from a spectrum of fibres which are metabolically suited to a wide range of functional demands. As judged from enzyme activity analyses of single fibres, the metabolic properties of fibres belonging to the same motor unit are similar or identical. It is likely, therefore, that the phenotype expression of muscle fibres is primarily under neural control. Differences in recruitment patterns of various motor units explain the wide range of metabolic properties as evidenced by pronounced variations in enzyme activities and enzyme activity ratios. There exist large overlaps between the activity spectra of various enzymes of anaerobic and aerobic metabolism in slow- and fast-twitch fibres. Nevertheless, these two major fibre classes can be distinguished by discriminative enzyme activity ratios (e.g. phospho-fructokinase/malate dehydrogenase, phosphofructokinase/3-hydroxyacyl-CoA dehydrogenase, fructose-1,6-diphosphatase/phosphofructokinase). Moreover, slow-twitch fibres display an H-type isozyme pattern of lactate dehydrogenase, whereas fast-twitch fibres are characterized by a predom-inance of LDH-5. No clear-cut differences exist between enzyme activity profiles and LDH isozyme patterns of the IIA and IIB subgroups of fast-twitch fibres. Comparative studies indicate that the metabolic properties of IIA and IIB fibres vary in different animal species. This observation supports the notion that metabolic and myosin-related properties of muscle fibres may be regulated independently. Due to relatively high turnover rates of enzymes of energy metabolism in muscle, changes in functional demands may be met by relatively rapid changes in metabolic properties. In view of these findings it is not surprising that muscle fibres display a spectrum of metabolic properties and represent stages within a dynamic equilibrium.
Power and efficiency of insect flight muscle
Authors: Ellington C. P.
Published: April 2021

The efficiency and mechanical power output of insect flight muscle have been estimated from a study of hovering flight. The maximum power output, calculated from the muscle properties, is adequate for the aerodynamic power requirements. However, the power output is insufficient to oscillate the wing mass as well unless there is good elastic storage of the inertial energy, and this is consistent with reports of elastic components in the flight system. A comparison of the mechanical power output with the metabolic power input to the flight muscles suggests that the muscle efficiency is quite low : less than 10%.
Metabolic and circulatory limitations to muscular performance at the organ level
Authors: Terjung R. L. , Dudley G. A. , Meyer R. A.
Published: April 2021

Within working muscle, development of conditions that directly influence exercise performance is dependent on many factors, including: intensity and duration of exercise, type of skeletal muscle fibres recruited, cardiovascular support to the working fibres and the inherent metabolic characteristics of the contracting fibres. In general, it is possible to identify factors that seem to alter exercise performance only at relatively intense exercise conditions. During prolonged moderately intense exercise (e.g. 70-80% maximal oxygen consumption for at least 60—90 min) decline in performance is related to the depletion of glycogen within the working muscle. Although the cause of muscle performance decline during very intense exercise is not known, an extreme acidosis is found, especially in fast-twitch muscle, which could significantly disrupt normal metabolic and contractile processes. During fatigue caused by intense contraction conditions, ATP content decreases (by approx. 50 %) and there is a stoichiometric production of IMP and ammonia in fast-twitch muscle. This loss in adenine nucleotide content is dependent on the severity of the contraction conditions relative to the functional aerobic capacity of the muscle fibre, since fast-twitch red (high mitochondria, high blood flow) and fast-twitch white (low mitochondria, low blood flow) muscles respond differently. In contrast, during similarly intense contraction conditions, rat slow-twitch muscle fibres maintain their ATP content and do not produce significant amounts of IMP. Indirect evidence suggests that a similar contrast between fibres occurs in humans during maximal exercise. Thus, there seems to be a fundamental difference between fast- and slow-twitch muscles in the management of their adenine nucleotide contents during intense contraction conditions. Whether this is related to the known differences in the fatigue process between these fibre types is not known.
Malleability of skeletal muscle in overcoming limitations: structural elements
Authors: Hoppeler H. , Lindstedt S. L.
Published: April 2021

Muscles allow animals to interact mechanically with their environment. The basic processes concerned with motion as well as the structure of the sliding filaments in muscle cells are found with little modification throughout the animal kingdom (Huxley, 1973). However, the energetic demand imposed on a muscle by the organism may vary greatly depending on the specific function of that muscle. Thus, both the heart and the diaphragm have to deliver high rates of mechanical energy continuously during the whole life-span of an animal, whereas other muscles, such as the gastrocnemius, are only briefly activated every once in a while. The present review analyses the malleability of the structural components of the energetic machinery of skeletal muscle cells with regard to the energetic demand placed upon them by the organism.
How flexible is the neural control of muscle properties?
Authors: Edgerton V. R. , Martin T. P. , Bodine S. C. , Roy R. R.
Published: April 2021

Since this classic report, there have been numerous studies which have essentially verified these initial findings. Many of the subsequent papers have addressed two major questions regarding the phenomenon of neural control of muscle properties. First, how does the nervous system exert its control over certain physiological and biochemical properties? Three principal means of neuronal control have been proposed: (1) the pattern (quality) of impulses; (2) the total number (quantity) of impulses; and, (3) a neurotrophic (nonactivity-related) mechanism (Buller et al. 1960). All three possibilities remain viable today. However, the most promising evidence suggests that impulse frequency (Salmons & Sreter, 1976) and quantity of impulses (Sreter, Pinter, Jolesz & Mabuchi, 1982; Jolesz & Sreter, 1981) could be responsible, at least in part, for differences in the speed-related properties of slow and fast muscles.
Adaptability of ultrastructure in the mammalian muscle
Authors: Eisenberg B. R.
Published: April 2021

All the skeletal muscle fibres taken from an adult mammal do not look alike. The structural differences are a result of adaptations which allow gradations in mechanical output to be achieved. The anatomy is described and the amounts of the subcellular components are measured by stereological techniques from electron micrographs. A population of normal, adult fibres is classified by the Z-line width, by the amounts of the mitochondria, T-system and terminal cisternae (TC), and by the isoforms of contractile proteins present. Classification of fibres by some of these ultrastructural components gives clusters named fast-twitch and slow-twitch types, but classification by other components gives a continuum of overlapping properties. Transformation from the fast- to the slow-twitch type or vice versa follows a specific alteration in the use of the fibre. The mechanical demand on the fibre is modified by changing the frequency of stimulation in the nerve with an implanted electrode. The time course of the changes in subcellular composition in the fibre during adaptation is followed for many weeks. Changes in the membrane systems begin within hours and are complete in days. Changes in the contractile proteins and metabolic systems begin in days and are complete in weeks. During these transitional phases of adaptation the fibres have an unusual complement of components never seen in a normal adult fibre. Extreme alterations, such as myofibril disassembly or supranormal amounts of mitochondria also result during some adaptive transitions. The aberrant appearance in the transitional fibres may be a result of doing the required mechanical work with a less than optimal set of proteins. At the end of the fibre type transformation, the fibre ultrastructure is indistinguishable from normal.
Component Permeabilities and Water Contents in Periplaneta Integument: Role of the Epidermis Re-Examined
Authors: Machin J. , Lampert G. J. , O’Donnell M. J.
Published: April 2021

Improved in vivo and in vitro techniques for measuring cuticular water permeability are described. Air flowing over a cuticle disc mounted in a holder, permitted elimination of unstirred layers, or corrections for them, for the first time. Conditions inside the holder were incompatible with the long-term health of the epidermal cells. Significantly, mean permeabilities of these discs did not differ from values obtained in vivo on the same cuticular plate.

Overall cuticular permeability was apportioned between endocuticle and combined epicuticle and exocuticle on the basis of measurements made before and after solvent extraction of lipids. Under identical activity gradients, endocuticle permeability was 35 to 40 times greater than the value for the other layer. Permeability of both component layers showed strongly non-linear relationships with ambient activity, with empirical proportionality to the reciprocal of vapour pressure lowering.

Cuticle water contents measured in activity gradient conditions showed significantly higher values in vivo than in vitro. The amount of water contained in the combined epicuticle and exocuticle was too small to measure.

We conclude that neither permeability nor water content data support the existence of a significant water barrier in the region of the epidermis.
Chromatophore Motor Units in Eledone Cirrhosa (Cephalopoda: Octopoda)
Authors: Dubas F. , Boyle P. R.
Published: April 2021

Innervation of chromatophore muscles of the octopus Eledone cirrhosa was investigated by stimulating nerve bundles in the skin with a suction electrode and monitoring chromatophore movements with a photo-cell or a video camera. Attention was focused on the organization of the chromato-phore muscle fibres into motor units. Individual muscle fibres respond to single electrical impulses with twitch-like contractions that do not facilitate with repetition, but summate to a smooth tetanus at about 10-15 Hz. At tetanic frequency, the degree of expansion of single chromatophores is always maximal. However, the number of expanded chromatophores can be graded by variations of either the stimulus voltage or frequency. Individual chromatophores and probably individual muscle fibres are part of several motor units. Chromatophores forming a given motor unit are found among chromatophores served by other motor axons. The motor units apparently form precise parts of natural patterning.
The Physiology of Wandering Behaviour in Manduca Sexta II. The Endocrine Control of Wandering Behaviour
Authors: Dominick Oliver S. , Truman James W.
Published: April 2021

Removal of the prothoracic glands early during the 5th instar of Man-duca sexta prevented the larvae from wandering and from further development. Infusion of 20-hydroxyecdysone (20-HE) into these larvae induced wandering behaviour. In intact larvae, induction of precocious wandering behaviour required a 20-HE infusion lasting longer than 5 h. Infused 20-HE induced maximal response (90%) when delivered at a rate of 0·06μgg–1 body weighth–1. At considerably higher concentrations (0·25μgg–1h–1 larvae performed brief, erratic behaviour or omitted wandering entirely. The latency between appearance of 20-HE and the onset of wandering was dose-dependent with a minimum of 11 h following infusion at 0·1 μgg–1 h–1. Latency was not affected by the duration of 20-HE infusion. The duration of induced wandering behaviour was proportional to the duration of 20-HE infusion. Minimal wandering behaviour lasted 2h following 20-HE infusions at 5 h, while infusions lasting 11 h induced 9 h of wandering behaviour. Several lines of evidence suggest that the effects of 20-HE accumulate over time and directly determine the duration of wandering behaviour. Many larvae exhibited a series of temporally distinct locomotor periods following various 20-HE infusion protocols, suggesting that a series of separate exposures to 20-HE can result in corresponding serial bouts of locomotion. Responsiveness to 20-HE appeared to be principally modulated by juvenile hormone. Allatectomy of 2nd, 3rd and 4th instar larvae removed juvenile hormone (JH) precociously from these stages and was followed several days later by precocious wandering behaviour. Likewise, application of the JH mimic, EGS, prior to 20-HE exposure or at the start of it, could prevent the behavioural induction. During the 5th instar, 20-HE became increasingly effective in inducing wandering as larvae grew larger than 5 g, the size at which JH normally begins to disappear from the haemolymph. Allatectomized 5th instar larvae responded directly to 20-HE a day sooner than larvae with normal JH titres, but before day 2 the effects of 20-HE on wandering behaviour appear to be indirect, requiring a latency greater than 24 h. Several processes, of which the elimination of JH is the last, appear to be required before 20-HE can induce wandering behaviour. Throughout the entire period when 20-HE was acting to induce wan-dering, the appearance of JH could prevent further induction of behaviour, but the effects of 20-HE which had already been established up to that time were expressed. Thus, application of EGS progressively later during the interval of 20-HE action was progressively less effective in reducing the length of wandering behaviour. The presence of EGS during wandering had no behavioural effect, indicating that only the induction of behaviour by 20-HE is sensitive to modulation by JH.
The Ultrastructure Of The Epicuticular Interference Reflectors Of Tiger Beetles (Cicindela)
Authors: Schultz T. D. , Rankin M. A.
Published: April 2021

Tiger beetles of the genus Cicindela exhibit iridescent structural coloration due to the presence of a non-ideal multilayer interference reflector located in the outermost 2 μm of the integument. The reflector is composed of alternating layers of electron-lucent and electron-dense material. This series of layers was distinguished from chitinous procuticle by its position, ultrastructure and solubility in dilute KOH. The reflector appears homologous with the inner epicuticle of current models. Measurements of surface reflectance, refractive index and the dimensions of the alternating layers suggests that the dense layer has a refractive index (RI) near 2·0 and may be a melanoprotein.
Electrophysiological Characterization of Peptidergic Neurosecretory Terminals
Authors: Cooke Ian M.
Published: April 2021

Electrical activity recorded intracellularly from peptidergic neurosecretory terminal dilatations in the sinus gland of crabs (principally Cardisoma guanhumi and C. carnifex) is described. Recordings were made from the neurohaemal organ in situ on the neural tissue of the isolated eyestalk and from isolated sinus gland-sinus gland nerve preparations. Verification that electrodes penetrated terminals was obtained by dye marking. Resting potentials ranged between –30 and –80 mV. Overshooting action potentials of long duration (5-20 ms at 1 / 2 amplitude) relative to those of non-secretory axons ( < 2 ms) were recorded in approximately 70 % of stable penetrations. Action potentials occurred spontaneously at slow (<0·2s−1) rates in 75% of penetrations. Sequential intra-and extracellular recordings with the same microelectrode, on the same terminal, indicate impulse generation by the terminal itself.

Extracellular stimulation of the axon tract evokes an all-or-none action potential at distinct threshold and latency. At rates of stimulation exceeding 5s−1, discrete fluctuations in the form of responses occur. Similar waveforms occur spontaneously and can be evoked by passing current through the electrode. They are interpreted to be electrotonically recorded activity of other parts of a complex axonal terminal arborization. Some, but not all, terminals exhibit impulse broadening (up to three-fold at 1/2 amplitude) during repetitive firing exceeding 1s−1. The same terminals show reduced impulse duration with hyperpolarization and broadened impulses with imposed depolarization. The changes are due to altered repolarization rates. Terminals sustain steady impulse firing at rates (up to 5 s−1) linearly related to the imposed depolarizing current.

Regenerative potentials, though of reduced rate of rise and amplitude, can be evoked by depolarizing current passed through the electrode during perfusion with salines having 1/2 normal [Na+], or containing tetrodotoxin (10∼6mol 1−1). However, these block axonal conduction. Nominally Ca-free saline causes increased spontaneity and depolarization of about 5 mV in half the preparations examined, but reaching 20 mV in the others, with resultant inactivation of regenerative activity. Impulses in low-Ca saline show alterations of the falling phase, it being faster initially and then slower than normal. Thus, while the action potentials of neurosecretory axons are Na dependent, the terminals support regenerative impulses mediated by both Na and Ca.
A Synchronous Insect Muscle With an Operating Frequency Greater Than 500 Hz*
Authors: Josephson Robert K. , Young David
Published: April 2021

The male cicada, Okanagana vanduzeei, produces a calling song with a pulse repetition frequency of 550 Hz. This sound is produced by a pair of tymbals, each of which is buckled by a large tymbal muscle. Males sing in full sun and the operating temperature of the tymbal muscles is 40–45 °C. Analysis of the songs of animals with the tymbal mechanism destroyed on one side, and of the sounds produced by directly manipula-ting a tymbal, indicates that the two tymbals normally buckle synchro-nously and that only one sound pulse is produced per tymbal muscle contraction. This implies that the contraction frequency of each tymbal muscle is 550 Hz. Recordings of calling songs from animals with implanted electrodes show that there is usually synchrony between left and right tymbal muscle contractions and that each tymbal muscle can operate at a frequency of about 550 Hz. The recordings also show that there is a 1:1 correlation between muscle electrical and mechanical activity, i.e. these muscles are synchronous and not asynchronous muscles. The ultrastructure of the tymbal muscle is clearly that of a very fast, synchronous muscle: the myofibrils are small, the sarcoplasmic reticulum is extraordinarily well developed, and the T-tubules lie at the 1/4 and 3/4 positions along the sarcomere. When set up for isometric recording, with their nerve supply severed, the tymbal muscles often show spontaneous electrical and mechanical oscillations. The frequency of these oscillations is strongly temperature dependent, and at higher temperatures approaches the normal operating frequency of the muscle. The tendency to oscillate is so strong that single twitches could only very rarely be evoked by electrical stimulation. A twitch duration of under 6ms was observed at 30°C. We conclude that the tymbal muscle of O. vanduzeei is indeed a synchronous muscle, albeit a highly modified one, capable of operating at 550 Hz. We suggest that the advantages of asynchronous muscles lie chiefly in their greater economy of structure and operation, rather than in an ability to operate at higher frequencies than synchronous muscles.
Uptake and Loss of Potassium by Rainbow Trout (Salmo Gairdneri) in Fresh Water and Dilute Sea Water
Authors: Eddy F. B.
Published: April 2021

Potassium turnover was studied in rainbow trout, Salmo gairdneri Richardson, adapted to fresh water or 22 %o sea water using 42K and 86Rb. Potassium space of the whole body increased with time and was about 5 mmol kg−1 after 20 h, while Rb+ space under the same conditions was only about 0·5 mmol kg−1, indicating slow penetration of body K+ by Rb +, especially in muscle and red blood cells. Potassium influx, measured by decrease in specific activity of the medium, was 0·07 mmol kg 1 h−1 in fresh water and 0·48 mmol kg−1 h−1 in 22 %o sea water; the values for eflflux were comparable, indicating that unfed fish are able to maintain K + balance. In both fresh water and dilute sea water, K+ fluxes are 5 % or less of the simultaneous Na+ and Cl− fluxes. The mechanism for K + fluxes is discussed in terms in K + -ATPases.