Search Results

You are looking at 1 - 9 of 9 items for

  • Author or Editor: Johan van Leeuwen x
  • Search level: All x
Clear All
In: Animal Biology

Abstract

We investigated the function of the m. hyohyoideus superior (MHS) and inferior (MHI) in the head of three carp (Cyprinus carpio L., 29.7 ± 2.1 cm FL ) during three movements (normal breathing, stressed movements and food uptake). Both muscle parts are located ventrally at the inner side of the operculum and branchiostegal rays and consist of red (mainly in MHI) and white (mainly in MHS) fibres. Contrasting views exist about the functional role of these muscles during ventilation and food uptake. Therefore, we analysed muscle activities of the MHS and MHI using electromyography (EMG) and measured the strain pattern of the MHS using sonomicrometry. Carp were also filmed from a ventral viewpoint using high-speed video at 250 frames s-1. EMG and sonomicrometry data showed an increase in muscle strain amplitudes, cycle frequency and (relative) stimulus duration while stimulus on- and off-times occurred earlier in the strain cycle from normal breathing to stressed movements to food uptake. The MHS and MHI were always simultaneously active. We concluded that: 1) the MHI is not responsible for high frequency movements (i.e. stressed movements and food uptake); 2) both muscle parts assist in the onset of opercular closing, and 3) the MHS and MHI do not act as antagonists in carp.

In: Animal Biology

Abstract

We present a numerical-experimental diffusion study in which we elucidate the spatial oxygen profile around and inside a zebra fish embryo in the pre-circulation stage (24-28 hpf). Lowest oxygen partial pressures are found in the head with a gradient of posteriorly increasing pressure along the midline of the embryo. Furthermore, this study shows the yolk mass to have a relatively high oxygen permeability as compared to the surrounding medium and the respiring tissue. The oxygen permeability of the respiring tissue in this stage is close to that of water. Knowledge of the details of the oxygen distribution are important for an understanding of vasculogenesis and angiogenesis, since oxygen levels influence the expression of endothelial growth factors.

In: Animal Biology

Abstract

We review current quantitative models of the biomechanics of bird sound production. A quantitative model of the vocal apparatus was proposed by Fletcher (1988). He represented the syrinx (i.e. the portions of the trachea and bronchi with labia and membranes) as a single membrane. This membrane acts as a valve that rapidly closes and opens during phonation. This model can be used as a basis to address comparative morphological and physiological questions. More recently, the syrinx was modelled as a simple modified oscillator. Many features of the sound were captured remarkably well. The parameter values, however, did not represent the distribution of the actual material properties of the syrinx. These models demonstrated the minimum number of parameters required to describe the essential dynamics of the sound signal. Furthermore, we address possible interesting future directions for modelling.

In: Animal Biology

Abstract

The orientation and organisation of collagen fibrils play an important role in the mechanical functioning of the articular cartilage (AC) that covers the surfaces in the diarthrodial joints. In the adult animal, typically an arcade like 'Benninghoff structure' is found. Because the remodelling capacity of the collagen network in the adult animal is limited, this Benninghoff structure needs to develop before the animal reaches maturity, and it needs to develop correctly. The aim of this study is to use quantitative polarised light microscopy (qPLM) and scanning electron microscopy (SEM) techniques to investigate if this Benninghoff structure is already present in the young animal, and to quantitatively investigate possible differences in collagen structure in the equine distal metacarpus of the young and adult animal. In total, 21 forelimbs of 13 horses are used. In animals of age 10 months and older, we find an arcade like Benninghoff structure for the collagen fibril network in both the qPLM and SEM study. The qPLM study shows that the collagen's predominant orientation is parallel to the articular surface throughout the entire cartilage depth in two animals directly after birth. These findings are supported by SEM results on a foal. We conclude that structural remodelling of the collagen network in AC occurs in the first months after birth. Because animals start with collagen parallel to the articular surface and need to remodel this structure to a Benninghoff architecture, and because collagen structure is an important parameter for AC mechanics and mechanobiology, these results suggest implications for AC epigenetics.

In: Animal Biology
Papers presented to the International Conference of the Leiden Institute for the Study of Religions (LISOR) held at Leiden 9-10 January 1997
This volume contains the papers read at the Leiden Conference on Canonization and Decanonization of 9-10 January 1997. The emphasis in this rich and wide-ranging contribution to the subject is on the processes of canonization and decanonization in several religions and on the phenomenon of religious canons as well.
It has two sections: (De)canonization and the History of Religions, and (De)canonization and Modern Society. In the first section processes out of which canons eventually emerge are highlighted in contributions devoted to particular religions, viz. African religions, Judaism and Christianity, Islam, Buddhism and Zoroastrianism. The articles of the second section are of particular relevance to the contemporary situation in the western world, dealing with aspects such as forms of the survival of a canon in processes of modernization, canonization and the challenge of plurality, and canonization and hermeneutics. The reader may benefit even more from this volume as it contains also An Annotated Bibliography on the subject.