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At least 73 records · Page 4Linked to original sources
PubMed1994

Electrical coupling and impulse propagation in anatomically modeled ventricular tissue.

Computer simulations were used to study the role of resistive couplings on flat-wave action potential propagation through a thin sheet of ventricular tissue. Unlike simulations using continuous or periodic structures, this unique electrical model includes random size cells with random spaced longitudinal and lateral connections to simulate the physiologic structure of the tissue. The resolution of the electrical model is ten microns, thus providing a simulated view at the subcellular level. Flat-wave longitudinal propagation was evaluated with an electrical circuit of over 140,000 circuit elements, modeling a 0.25 mm by 5.0 mm sheet of tissue. An electrical circuit of over 84,000 circuit elements, modeling a 0.5 mm by 1.5 mm sheet was used to study flat-wave transverse propagation. Under normal cellular coupling conditions, at the macrostructure level, electrical conduction through the simulated sheets appeared continuous and directional differences in conduction velocity, action potential amplitude and Vmax were observed. However, at the subcellular level (10 microns) unequal action potential delays were measured at the longitudinal and lateral gap junctions and irregular wave-shapes were observed in the propagating signal. Furthermore, when the modeled tissue was homogeneously uncoupled at the gap junctions conduction velocities decreased as the action potential delay between modeled cells increased. The variability in the measured action potential was most significant in areas with fewer lateral gap junctions, i.e., lateral gap junctions between fibers were separated by a distance of 100 microns or more.

Action Potentials↗
PubMed1992

Transmaxillary-transnasal approach to the anterior clivus: a microsurgical anatomical model.

Numerous procedures to expose the anterior clival region have been described, including the transoral, transcervical, transseptal-transsphenoidal, transantral, transnasal, bilateral Le Fort I maxillotomy, transbasal, transpalatal, and modifications of the Caldwell-Luc approach. Despite the large number of surgical options available, it may be necessary to have wider access to the midline skull base than these approaches provide. We have developed a microsurgical transmaxillary-transnasal approach to the anterior clivus that has been studied in both dry skull and cadaveric preparations and used clinically. The surgical technique has four stages: 1) antromaxillary; 2) nasal; 3) sphenoidal; and 4) clival. The wider access of this approach is achieved mainly by an osteotomy of the frontal process of the maxilla, which transforms the nasal cavity and the antrum into a single cavity while preserving the functional anatomy of the nose. Cosmesis is preserved by replacement of the cartilaginous nasal septum and the frontal process at the end of the procedure. The technique provides the good cosmetic results of the sublabial approaches and prevents vascular and neural injury in the same way that other anterior approaches do. This transmaxillary-transnasal technique may be used in combination with other approaches for extensive tumors.

Adolescent↗
PubMed2002

A micro-anatomical model of the distribution of myocardial endomysial collagen.

Myocardial connective tissue probably provides passive support for regulating heart tensile strength and stiffness and ultimately for controlling heart mechanics through its endomysial part. However, endomysial collagen micro-arrangement is still a matter of debate. In order to define the fine distribution of left ventricle endomysial collagen, we applied the NaOH-scanning electron microscopy (SEM) maceration method (one of the techniques of choice for studying collagen micro-arrangement) to rabbit heart. Gomori-reticulum staining was used for correlated light microscopy (LM) observations. The SEM-NaOH method allowed isolation of collagen by removing other extracellular matrix components and cells and preserved collagen structure and position. Endomysial collagen appeared arranged in laminae that delimited the lacunae that were left empty by macerated myocytes and small vessels (mostly capillaries). These laminae were formed by reticular fibers, as confirmed by LM observations of Gomorireticulum-stained samples, and were organized in irregularly meshed networks made of thin (single) and thick (composed) filaments. In longitudinal views, collagen laminae extended the entire length of lacunae. In transversal views, the cut surface of the laminae appeared to be made of collagen bundles. These observations provide an updated microanatomical view of endomysial collagen distribution, which integrates previous studies. This model is based on the evidence that collagen laminae enveloped the surface of small vessels and myocytes. Thus, a type of myocyte-myocyte or capillary-myocyte "laminar connection" anchored to the entire cell length here is emphasized, rather than a type of "strut connection" anchored to defined loci, as usually described. This structure explains better how endomysium may provide the necessary support for heart compliance and protection against overstretch.

Animals↗
PubMed1992

The three-dimensional architecture of the myosalpinx in mammals: an anatomical model for a functional hypothesis.

Direct visualization of the three-dimensional architecture of the tubal musculature (myosalpinx) was made possible by a technique involving chemical digestion of interstitial connective tissue, followed by ultrasonic microdissection and final observations under the scanning electron microscope. The isthmic myosalpinx in the guinea pig, rabbit and in humans consists of muscular bundles that tend to lie longitudinally, circularly or oblique. The muscular bundles along the tubal wall change direction, branch and intermingle with one another, giving rise to an irregular network in which distinct layers are not readily distinguishable. In the ampulla, the muscle bundles form a very irregular three-dimensional network of fibres that follow different orientations. The authors suggest a primary role for such a structure in the random pendular transport of the gametes as well as in the denudation of the egg by deformation of the myotubal wall.

Animals↗
PubMedDate not supplied

[Total cranio-facial anatomical model of plio-pleistocene hominids].

For a correct assessment of the fossil specimens are analysed ten characters or structural complexes of neuro - and splancno - cranium. Not individual characters but a total pattern, according to Le Gros Clark's original concept, provide a positive identification of hominid single taxon. Following items are examined: 1) facial prognathism; 2) mid-facial architecture; 3) nasal bone, fronto-nasal and fronto-maxillary suture; 4) frontal region morphology; 5) temporal lines and cranial cresting; 6) occipital and nuchal plane; 7) steepness of nuchal plane, foramen magnum position; 8) skull base diagrams; 9) mastoid process and neighbouring regions; 10) size and form of mandibular fossa. To conclude: it is possible a taxonomic classification of plio-pleistocenic hominid specimens on the basis of an analysis of the "total morphological pattern".

Animals↗
PubMed1979

A simple model for anatomic bone scanning studies.

A simple anatomic model for studying the scintigraphic appearance of various skeletal structures is described. The technique makes use of the fact that technitium pyrophosphate uptake in bone occurs by chemisorption to the surface of crystals in the bone matrix. By soaking clean bones in solutions of technetium pyrophosphate they can be rendered radioactive and subsequently studied by various imaging techniques.

Bone and Bones↗
PubMed1992

A new oral surgery teaching model.

An anatomical model for teaching the practical aspects of routine oral surgery in a clinical or laboratory environment, is described. Replaceable sections allow the model to be rapidly re-used so that successive students may practise procedures such as incisions, flap reflection, bone removal, tooth removal, apicectomy and suturing. Keeping the cost per procedure to a minimum was considered to be of fundamental importance and this has been achieved through the use of 'factory produced' replacement parts.

Equipment Design↗