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Biomedical subjects

J L van Leeuwen

Publications and source records attributed to J L van Leeuwen.

At least 19 recordsLinked to original sources
PubMed2006

Endurance exercise differentially stimulates heart and axial muscle development in zebrafish (Danio rerio).

Mechanical load is an important factor in the differentiation of cells and tissues. To investigate the effects of increased mechanical load on development of muscle and bone, zebrafish were subjected to endurance swim training for 6 h/day for 10 wk starting at 14 days after fertilization. During the first 3 wk of training, trained fish showed transiently increased growth compared with untrained (control) fish. Increased expression of proliferating cell nuclear antigen suggests that this growth is realized in part through increased cell proliferation. Red and white axial muscle fiber diameter was not affected. Total cross-sectional area of red fibers, however, was increased. An improvement in aerobic muscle performance was supported by an increase in myoglobin expression. At the end of 10 wk of training, heart and axial muscle showed increased expression of the muscle growth factor myogenin and proliferating cell nuclear antigen, but there were major differences between cardiac and axial muscle. In axial muscle, expression of the "slow" types of myosin and troponin C was increased, together with expression of erythropoietin and myoglobin, which enhance oxygen transport, indicating a shift toward a slow aerobic phenotype. In contrast, the heart muscle shifts to a faster phenotype but does not become more aerobic. This suggests that endurance training differentially affects heart and axial muscle.

Animals↗
PubMed2006

Syringeal muscles fit the trill in ring doves (Streptopelia risoria L.).

In contrast to human phonation, the virtuoso vocalizations of most birds are modulated at the level of the sound generator, the syrinx. We address the hypothesis that syringeal muscles are physiologically capable of controlling the sound-generating syringeal membranes in the ring dove (Streptopelia risoria) syrinx. We establish the role of the tracheolateralis muscle and propose a new function for the sternotrachealis muscle. The tracheolateralis and sternotrachealis muscles have an antagonistic mechanical effect on the syringeal aperture. Here, we show that both syringeal muscles can dynamically control the full syringeal aperture. The tracheolateralis muscle is thought to directly alter position and tension of the vibrating syringeal membranes that determine the gating and the frequency of sound elements. Our measurements of the muscle's contractile properties, combined with existing electromyographic and endoscopic evidence, establish its modulating role during the dove's trill. The muscle delivers the highest power output at cycle frequencies that closely match the repetition rates of the fastest sound elements in the coo. We show that the two syringeal muscles share nearly identical contraction characteristics, and that sternotrachealis activity does not clearly modulate during the rapid trill. We propose that the sternotrachealis muscle acts as a damper that stabilizes longitudinal movements of the sound-generating system induced by tracheolateralis muscle contraction. The extreme performance of both syringeal muscles implies that they play an important role in fine-tuning membrane position and tension, which determines the quality of the sound for a conspecific mate.

Animals↗
PubMed2005

Identification and characterisation of two runx2 homologues in zebrafish with different expression patterns.

Genome and gene duplications are considered to be the impetus to generate new genes, as the presence of multiple copies of a gene allows for paralogues to adopt novel function. After at least two rounds of genome/gene duplication, the Runt gene family consists of three members in vertebrates, instead of one in invertebrates. One of the family members, Runx2, plays a key role in the development of bone, a tissue that first occurs in vertebrates. The family has thus gained new gene function in the course of evolution. Two Runx2 genes were cloned in the vertebrate model system the zebrafish (Danio rerio). The expression patterns of the two genes differ and their kinetics differ up to four fold. In addition, splice forms exist that are novel when compared with mammals. Together, these findings comprise opportunities for selection and retention of the paralogues towards divergent and possibly new function.

5' Untranslated Regions↗
PubMed2005

Effects of decreased muscle activity on developing axial musculature in nicb107 mutant zebrafish (Danio rerio).

The present paper discusses the effects of decreased muscle activity (DMA) on embryonic development in the zebrafish. Wild-type zebrafish embryos become mobile around 18 h post-fertilisation, long before the axial musculature is fully differentiated. As a model for DMA, the nic(b107) mutant was used. In nic(b107) mutant embryos, muscle fibres are mechanically intact and able to contract, but neuronal signalling is defective and the fibres are not activated, rendering the embryos immobile. Despite the immobility, distinguished slow and fast muscle fibres developed at the correct location in the axial muscles, helical muscle fibre arrangements were detected and sarcomere architecture was generated. However, in nic(b107) mutant embryos the notochord is flatter and the cross-sectional body shape more rounded, also affecting muscle fibre orientation. The stacking of sarcomeres and myofibril arrangement show a less regular pattern. Finally, expression levels of several genes were changed. Together, these changes in expression indicate that muscle growth is not impeded and energy metabolism is not changed by the decrease in muscle activity but that the composition of muscle is altered. In addition, skin stiffness is affected. In conclusion, the lack of muscle fibre activity did not prevent the basal muscle components developing but influenced further organisation and differentiation of these components.

Animals↗
PubMed2001

Consequences of forced convection for the constraints on size and shape in embryos.

Previously, predictions of the maximum size of biological objects based on oxygen availability have been made for both zero and infinite water velocity around the object. In reality, however, water velocity is always intermediate between zero and infinity. We predicted maximum size and optimal shape of biological objects, pending the velocity of water around them. We assumed oxygen inside the object to be transported by diffusion and outside the object by diffusion and convection. Fick's first law of diffusion describes the inner transport. For the outer transport, we relied on semi-empirical relations between mass transport and flow conditions (Friedlander's equations). To keep mathematical complexity acceptable, we restricted ourselves to the analysis of a sphere and a cylinder in cross flow. If water velocity is low, a spherical shape is most favourable for gas exchange. If water velocity is high, an elongated and flattened shape is more favourable. A size-dependent intermediate velocity exists where shape does not matter (10(-4) m s(-1)for teleost embryos). Teleost embryos are typically exposed to flow velocities equal to or larger than 10(-4) m s(-1), making an elongated shape more favourable than a spherical one. Although teleost eggs are typically spherical, the oxygen-consuming embryos inside are indeed elongated.

Animals↗
PubMed1999

Neuromuscular control: introduction and overview.

This paper introduces some basic concepts of the interdisciplinary field of neuromuscular control, without the intention to be complete. The complexity and multifaceted nature of neuromuscular control systems is briefly addressed. Principles of stability and planning of motion trajectories are discussed. Closed-loop and open-loop control are considered, together with the inherent stability properties of muscles and the geometrical design of animal bodies. Various modelling approaches, as used by several authors in the Philosophical Transactions of the Royal Society of London, Series B, May 1999 issue, such as inverse and forward dynamics are outlined. An introductory overview is presented of the other contributions in that issue.

Animals↗
PubMed1996

State-space analysis of a myocybernetic model of the lower urinary tract.

To study the control of the lower urinary tract, the state space of the myocybernetic model by Bastiaanssen et al. (1996) is analysed. This model is able to respond to input signals from a neural network and includes descriptions of the muscle dynamics of both the detrusor in the bladder wall and the urethral sphincter. The equilibrium states of the model for constant input signals were found by evaluation of the roots of calculated flow curves. Two types of equilibrium states could be distinguished: (i) the inflow and the outflow of the bladder are both equal to zero and (ii) the bladder in- and outflow are both equal to a prescribed small constant flow from the ureters into the bladder. The first type of equilibrium features a very high bladder pressure, which in vivo could result in a reflux of urine into the ureters. The second type shows a constant loss of urine. For different combinations of constant input signals, several stable equilibrium states of both types were found. The neural controller should avoid these states so that the lower urinary tract fulfils either its storage or its voiding function. Therefore, the trajectory through the state space of a simulated normal filling and micturition event was evaluated here. It appeared that equilibrium states were avoided by rapid changes of the input signals. The behaviour of the model outside the normal trajectory is compared with neurologic urinary tract disorders. Several pathological behaviours are in qualitative agreement with the model predictions.

Computer Simulation↗
PubMed1996

A myocybernetic model of the lower urinary tract.

A biomechanical model of the lower urinary tract which is able to respond to input signals from a neural network is presented. The neural input is the starting point in the description of the relationships between the various physical parameters in the mechanical model of the bladder and the urethra. The cybernetics of the lower urinary tract are described on the basis of the muscle dynamics of simple models of both the detrusor in the bladder wall and the urethral sphincter. The urethral sphincter is not described as a variable resistance, like in other biomechanical models of the lower urinary tract, but is described on the basis of striated muscle dynamics. The forces produced by the detrusor and the urethral sphincter give rise to the bladder pressure and the urethral pressure. Using quasi-steady assumptions, the flow rate of urine is calculated as a result of the pressure difference between the bladder and the urethra. Parameters like the bladder volume, the flow rate and the pressure in the bladder can be compared with clinical data of urodynamic measurements. Simulation results show that the model is able to mimic both a filling and an emptying behaviour which resembles the behaviour of the lower urinary tract. By increasing the resistance of the urethra, a behaviour model of the lower urinary tract appears which is comparable with the pathology of urethral obstruction. A sensitivity analysis of various parameters in the model leads to a better understanding of the biomechanics of the lower urinary tract.

Biomechanical Phenomena↗
PubMed1996

A two dimensional model for the prediction of muscle shape and intramuscular pressure.

Traditional pennate skeletal muscle models with straight fibres and straight tendinous sheets cannot assume realistic muscle shapes and are unsuitable for predicting intramuscular pressure. The two dimensional models proposed here have flexible fibres and tendinous sheets of which the curvatures are in mechanical equilibrium with the intramuscular pressure distribution. Analytical relationships between fibre stress, pressure, curvatures and lengths of fibres and tendinous sheets have been derived based on physical laws and functional demands. These relationships were used to generate unipennate muscle shapes and to calculate pressure distributions. The results compare well with the shapes of the medial gastrocnemius muscles of man and cat and with maximum intramuscular pressures as reported in the literature.

Animals↗
PubMed1993

Learning procedure in a neural control model for the urinary bladder.

A continuous neural network coupled to a dynamical model of the urinary bladder is defined. The neural network is trained to control the bladder model to track a prescribed volume fluctuation, by adjusting weights and time constants. The gradients of the error in the output neurons of the neural network are unknown. Therefore, the learning procedure discussed here minimizes the error functional without using gradient descent.

Animals↗
PubMed1993

The tensile testing machine applied in the study of human nerve rupture: a preliminary study.

A tensile testing machine was used to provoke lesions of fixed and unfixed brachial plexus nerves. The forces and mechanical work were measured before and during rupture. Fixed nerves resist continued tensile forces better than unfixed nerves do. Increasing the speed of the tensile forces results in a decrease of the extension a brachial plexus nerve can withstand. The mechanical work needed to start rupture is equal to the mechanical work used to complete rupture of the nerve.

Biomechanical Phenomena↗
PubMed1992

Knee muscle moment arms from MRI and from tendon travel.

We tested magnetic resonance imaging (MRI) as a means to collect geometric data for moment arm estimation. A knee specimen in five successive flexion postures was scanned by MRI, while simultaneously tendon positions of loaded muscles were measured (long head of biceps femoris, lateral and medial gastrocnemius, gracilis, rectus femoris, sartorius, semimembranosus, semitendinosus, and tensor fasciae latae). Discrete rotation centres were derived from MRI pictures. Moment arms were estimated as the distances from these centres to the tendons. The ratio of tendon travel over the increment of joint angulation was the alternative, more reliable estimate of the moment arm. An important principal shortcoming of MRI is the impossibility of accounting for force distribution in taut tissue. As a consequence, for some muscles, considerable inaccuracies in moment arm estimation are found in a relatively small range of joint angulation (up to about 30% for the rectus femoris and semimembranosus). For the tensor fasciae latae, the moment arm cannot be estimated by MRI, while the estimate by tendon travel is unreliable owing to the deformability and attachments of the fascia lata.

Aged↗
PubMed1991

Optimum power output and structural design of sarcomeres.

A model of a "general" sarcomere is presented for the calculation of power output as a function of (i) contraction range, (ii) contraction velocity, (iii) muscle fibre stimulation (active state) and (iv) structural parameters of the sarcomere (i.e. lengths of actin, myosin, and bare zone on myosin, and thickness of the Z-disc). The model is applicable to virtually all types of striated muscle fibres. By computer simulation, particular combinations of actin and myosin lengths were found that maximize the specific power output for particular functional demands, specified in terms of contraction range and contraction velocity. The accuracy of the prediction of the optimum sarcomere design by the model depends on the quality of its input, i.e. the available knowledge of the in vivo spectrum of contraction velocities and sarcomere excursions. Predictions of sarcomere design from model simulations were compared with ultrastructural data from the literature. With the present model, the complete variation in the ratio of myosin length over actin length (from about 1.05 down to 0.65, as observed in insect and vertebrate sarcomeres) can be explained as a series of adaptations for optimum power output from a small to a large contraction range, respectively.

Animals↗
PubMed1991

Active force-length relationship of human lower-leg muscles estimated from morphological data: a comparison of geometric muscle models.

Muscle fibre lengths, pennation angles, and sarcomere lengths were measured (the latter by a diffraction technique) for each of the muscles of three embalmed lower-leg specimens. From these data and filament lengths from Walker & Schrodt (1973), the optimum fibre lengths were determined. Relationships between length and active force (at full activation) of the lower-leg muscles were calculated by use of (i) a unipennate muscle model, (ii) a bipennate model, and (iii) bipennate models in which the cosine of the pennation angle is approximated as length independent. It is concluded that the first two models are equally useful and that the use of the last models is discouraged in case of strongly pennated muscles. Non-uniformity of fibre parameters within one muscle appears to have little effect on the force-length relationship.

Aged↗
PubMed1990

Shock absorption of below-knee prostheses: a comparison between the SACH and the Multiflex foot.

Shock waves were measured during walking on a treadmill on the metal tube of a below-knee KBM prosthesis, provided either with a SACH foot or with a Multiflex foot. Accelerations were measured in the axial direction and the dorso-ventral direction, about 160 mm proximal to the sole of the shoe. The accelerations had comparable amplitudes to those measured on normal legs. Dorso-ventral amplitudes (order of magnitude 4 g) were generally higher than the axial amplitudes. For some patients, the SACH foot gave much higher axial accelerations than the Multiflex foot did. In the dorso-ventral direction, the SACH foot showed a moderate resonance phenomenon in the autospectral density function in the range of 40-50 Hz. The Multiflex foot showed a more variable behaviour. For both types of feet, components above 65 Hz were negligible.

Adult↗
PubMed1990

Estimation of instantaneous moment arms of lower-leg muscles.

Muscle moment arms at the human knee and ankle were estimated from muscle length changes measured as a function of joint flexion angle in cadaver specimens. Nearly all lower-leg muscles were studied: extensor digitorum longus, extensor hallucis longus, flexor digitorum longus, flexor hallucis longus, gastrocnemius lateralis, gastrocnemius medialis, peroneus brevis, peroneus longus, peroneus tertius, plantaris, soleus, tibialis anterior, and tibialis posterior. Noise in measured muscle length was filtered by means of quintic splines. Moment arms of the mm. gastrocnemii appear to be much more dependent on joint flexion angles than was generally assumed by other investigators. Some consequences for earlier analyses are mentioned.

Achilles Tendon↗