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At least 1,675 records · Page 93Linked to original sources
PubMed2001

Finite element modeling of the 3D otolith structure.

A 3D finite element model (FEM) of the mammalian utricular otolith corresponding to spatial structure, shape and size of the otolith from the guinea pig was developed. The otolithic membrane (OM) was considered as consisting of gel and otoconial layers. The macular surface was approximated as a plane. The deformation of the OM under static loads such as gravity and the change of endolymphatic pressure was analyzed using the FEM for different mechanical parameters of the OM and for different gravity vector orientations. The analytical dependence of OM displacements caused by the acceleration parallel to the macular plane was obtained. By comparison of the results of calculations with the known experimental data Young's modulus of the gel layer was estimated to be of order of 10 N/m(2). It was shown that static loads result in 3D local otolith displacements inhomogeneously distributed along the macular surface and across otolith thickness. Their distribution depends on the geometrical and mechanical parameters of the otolith components. The influences of the finite size of the OM, the Young's modulus, Poisson's ratio and thickness of the gel layer on the local displacements distribution of the OM were analyzed. The results of simulation suggest that: a) the Young's modulus of the thin lowest part of the gel layer adjacent to the macular surface is much smaller than that of the rest of the OM; b) the structure of the border is designed to reduce the spatial inhomogeneity of the gel layer displacement; c) a change of the endolymphatic pressure may result in significant deformation of the OM.

Animals↗
PubMedDate not supplied

[The evolution of the structure of the neocortex in mammals: a new theory of cytoarchitecture].

INTRODUCTION: The evolution of the structural organization of the mammalian neocortex can only be appreciated studying its ontogenetic development. DEVELOPMENT: We studied its evolution in embryos of different mammals (hamster, mouse, rat, cat and man) using the Golgi method. Development of the neocortex starts with the establishment of a primordial plexiform layer (PPL) in the telencephalus. This PPL represents a primitive cortical organization which is shared by amphibians, reptiles and mammals. From the PPL derived: the layer 1 with its elements including: the Cajal Retzius cells (CR) and primitive afferent fibres of a possibly origin in mesencephalic nuclei and the elements the interstitial cells and afferent fibres of the subplaca. The formation of the PPL is a prerequisite for the subsequent formation of the cortical plate (CP) from which the remaining layers of the neocortex derived. The ascending neuronal migration, the morphology of pyramidal neurons and the inside outside arrangement of neurons within the CP are evolutionary processes controlled by the CR cells. These neurons secrete a glycoprotein reelin which attracts the migrating neurons toward the first layer. All migrating neuroblasts, guided by the radial glia, must reach layer 1, establish contacts with the CR cells, develop an apical dendrite and become pyramidal cells. Without losing either their original contact with layer 1 or their cortical level, each neuron has to elongate its apical dendrite to accommodate the arrival of subsequent neurons, such that all develop a common initial pyramidal morphology. Older neurons have longer apical dendrites and deeper cortical level than the newer ones. The subsequent morphological and functional maturation of the CP neurons also follows an ascending progression and is under thalamic control. Two basic types of neurons develop in the neocortex following its ascending stratification. Some neurons maintain their original contact with the first layer to become the pyramidal cells. Others lose their original contact with layer 1 and become stellate interneurons. These neurons are free to develop specific size, spatial morphology and synaptic endings. The CP is a mammalian innovation and represents a biologically open and stratified nucleus which adds, during mammalian evolution, new pyramidal cell strata to those already present. CONCLUSIONS: Based on the above observations, we propose a new cytoarchitectural theory and nomenclature for the structural evolution of the mammalian neocortex. The theory emphasizes the ascending structural and functional stratification of the mammalian neocortex and the increase in the number of pyramidal cell strata reflecting the motor needs of each species.

Animals↗
PubMed2001

[Anatomy of the urethral sphincteric vesico-prostatic complex].

As 27 different names have been proposed for the components of the urethral sphincter, it is difficult to build a clear anatomical model of it. Starting from a review of the literature and from some personal observations of surgical anatomy, our aim is to draw a vision as much organic as possible of the anatomy of the urethral sphincter. The components of the urethral sphincter are: the bladder neck (preprostatic sphincter), the smooth muscle urethral sphincter, the rhabdosphincter and levator ani muscle. Recently the rhabdosphincter has been proposed as a vertical structure that extends from the pelvic cavity (bladder base) to the perineal cavity. It can be round-shaped or omega-shaped. The anterior insertions are along the anterolateral aspect of the prostate (superiorly) and on the perineal fascia (inferiorly). The posterior insertions are on the Denonvilliers fascia and posterior aspect of the prostatic apex (superiorly) and on the central perineal tendon (inferiorly). The rhabdosphincter has strong means of fixations: anteriorly it is fixed to the pubis by the pubo-urethral ligaments, posteriorly it is supported by the medial fibrous raphe of the perineum. The anteromedial fibres of levator ani muscle are involved in the continence mechanism by their strong relation with the rhabdosphincter and the prostate.

Humans↗
PubMed1995

[Bite mark analysis. Part 1. Methods and overview].

Criminal cases in which a suspect or a victim has left his or her teeth marks on another person or on an inanimate object such as a candy bar, an apple, cheese or even a beer can seem to occur more frequently. Testifying to the similarity or dissimilarity of a suspect's dentition to the bite mark in question is probably the most unique contribution that forensic dentistry makes to the judicial inquiry. This is a grave responsibility because a defendant's life or freedom may depend on the testimony given by the forensic odontologist in court.

Bites, Human↗
PubMed1975

[Experience in the use of electrified stands in the teaching of anatomy courses].

The paper reports the principles of arrangement and the estimation of efficiency of electrified training stands elaborated at the department. The work of the stand "Conducting pathways" is based on utilization of a distributing device which, due to different length of plates on the rotating disc, switches on a successive chain of lamps imitating conducting pathways. The stand "Human skeleton" is based on the principle of direct searching with use of a decade step-by-step switch (D55-100). The most complex in arrangement and efficient in use is the stand "Muscular system". The ruling diode matrix of this stand consisting of 450 diodes makes the electric impulse travel in the given strictly restricted direction. A special device permits controlling and estimating the process of learning the material.

Anatomy↗
PubMed2001

Implant placement in the vertically enhanced ridge--a surgical and restorative interdisciplinary approach.

A diagnostic and therapeutic approach is offered to enable the surgeon and restorative dentist to successfully install endosseous implants into the vertically enhanced ridge. The strategy involves the use of diagnostic and surgical templates to aid in the creation of positive osseous architecture followed by the vertical orientation of the endosseous implant(s). This effort provides optimal hard-tissue and soft-tissue form for the creation of the most favorable crown profiles for implant-supported prostheses.

Alveolar Bone Loss↗
PubMed2001

Establishing a nursing student learning center for women's reproductive health in Nepal.

The goal of this paper is to describe the establishment of a self-sustaining Student Learning Center (SLC) employing humanistic anatomical models to aid in the teaching of family planning and reproductive health clinical skills to nursing students in Nepal. In response to a local needs assessment a plan was developed to implement more thorough training of nursing students in family planning clinical skills. Nepalese nursing leaders worked together with a U.S. Non-Governmental Organization (NGO) to implement this project. This paper details the need for the SLCs, the content and structure of the SLCs, and the process of establishing an SLC at Tribhuvan University, Maharjgunj Nursing Campus in Kathmandu, the largest of all nursing campuses in Nepal.

Education, Nursing↗
PubMedDate not supplied

Assessment of accuracy of navigated implant placement in the maxilla.

PURPOSE: The use of computed tomography (CT) based intraoperative navigation has greatly improved surgery in many specialties. In this study, the precision of the SMN system (Zeiss, Oberkochen, Germany) for navigated drilling and following implant placement in the maxilla was evaluated. This study should demonstrate the suitability of navigation systems for computer-assisted implantation in the maxilla to avoid perforation of the maxillary sinus. MATERIALS AND METHODS: Sixty target drillings were carried out on 10 standardized polyurethane milling models after CT scanning. The models were produced with cranial open maxillary sinuses. The CT scans were performed with a slice distance of 1 mm. Then the CT data were transferred to the workstation of the SMN system and registration of the reference markers (fiducials) for superposition of the native and CT model was done. Referencing of the model was performed with the aid of a drilling tool. This drilling tool was used for later navigation-assisted drilling into the maxilla. The target of drilling was the maxillary sinus floor. The aim was to come as near as possible without perforation. The distance from the bottom of the drilling holes to the maxillary sinus floor was measured after sectioning of the model. In another 10 models, implants were placed after performing 60 navigated drilling holes. RESULTS: In the first part of the study, an average drilling depth of 6.97 mm and a mean distance to the sinus floor of 0.11 mm (standard deviation = 0.2) was found. In 13 specimens, the inferior border of the sinus was perforated. In the second part of the study, a perforation of the sinus floor by the implants was seen in 47 cases. The mean distance to the maxillary sinus was 0.25 mm (standard deviation = 0.2). DISCUSSION AND CONCLUSIONS: High precision of CT-based navigation for controlled preimplant drilling was seen, but a high incidence of penetrations into the maxillary sinus was caused by the subsequent implant placement.

Alveolar Bone Loss↗
PubMedDate not supplied

[Structure of the cerebral cortex. Intrinsic organization and comparative analysis of the neocortex].

We review our present knowledge on the intrinsic organization of the neocortex based on studies carried out with the Golgi method in several mammalian species. An outline is presented on certain general aspects of the termination of specific afferent fibers in layer IV in insectivora, rodents, carnivora and primates. The principal components of the cerebral cortex have been classified in two broad types: pyramidal cells, which account for nearly 70% of the total population, and intrinsic neurons. We review different morphological characteristics of pyramidal cells and intrinsic neurons with a full description of cell varieties, dendritic morphology and several aspects of synaptic connectivity of intrinsic neurons in comparison between different species. Special attention has been paid to the description of spinous stellate cells which seems unique for a given animal species. We have reviewed intrinsic cortical circuits linking several neocortical layers, the distribution of dendritic plexuses, and the excitatory and inhibitory synaptic connections established between various neuronal categories. We finally review modern concepts of functional neocortical architecture based on the modular organization of the cerebral cortex, concluding that the cerebral cortex is rather uniform at en elementary level but the differences appear substantial when the comparison is made between different species.

Animals↗
PubMed2002

Quantitative comparison of CFD predicted and MRI measured velocity fields in a carotid bifurcation phantom.

Steady flow of a blood mimicking fluid in a physiologically realistic model of the human carotid bifurcation was studied using both magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) modelling techniques. Quantitative comparisons of the 3D velocity field in the bifurcation phantom were made between phase contrast MRI measurements and CFD predictions. The geometry for the CFD model was reconstructed from T(1) weighted MR imaging of the test phantom. It was found that the predicted velocity fields were in fair agreement with MR measured velocities. In both the internal and external carotid arteries, the agreement between CFD predictions and MRI measurements was better along the inner-outer wall axis with a correlation factor C>0.897 (average 0.939) where the velocity profiles were skewed, than along the anterior-posterior axis (average correlation factor 0.876) where the velocity profiles were in M-shape.

Carotid Arteries↗
PubMed2002

Use of a human patient simulator for the advanced trauma life support course.

A highly anticipated and rewarding component of the Advanced Trauma Life Support (ATLS) program is the surgical skill station. Logistic, societal, and economic issues have resulted in development of human patient simulators (HPSs) as an alternative to the animal model. We studied initial student reaction to a simulator designed for this skill station. Fourteen participants in an ATLS Provider course completed the standard surgical skill stations and an experimental station using the Simulab Trauma Man HPS. After completion of the stations the students were asked to complete a 13-point satisfaction survey using a modified Likert scale (1 = strongly negative/dissatisfied, 5 = strongly positive/satisfied). Overall response was favorable. Students found the HPS to be superior to the animal model in teaching surgical airways [mean 3.64; standard deviation (SD) 0.93] and for management of pneumothorax (mean 3.86; SD 0.77). The students felt the HPS would be useful in ATLS and should be included as an option in training (mean 4.07; SD 0.92). Preliminary experience with an interactive HPS to teach the ATLS surgical skill station is well received by students when compared with standard methods. This strong acceptance supports inclusion of simulators in teaching ATLS skills.

Animals↗
PubMed2002

Lessons from east Arnhem land. Improving adherence to chronic disease treatments.

BACKGROUND: It is generally accepted that adherence or compliance to medical therapy can be poor in indigenous Australian communities. OBJECTIVE: This paper describes approaches and techniques to improve adherence that have been gleaned from four and a half years of clinical experience in the remote district of East Arnhem Land. DISCUSSION: First, the importance of gaining trust and credibility with a community is discussed. Approaches to gain that trust are then described. It is critical to overcome the considerable language and world view barriers that exist to good communication. The use of anatomical models and high quality illustrations combined with the development of 'key language concept' in the indigenous language have achieved some success in this area.

Australia↗
PubMed1968

Correlation of dose rate and spectral measurements in the Inner Van Allen Belt.

Dose rate measurements and the charged particle environment of the Inner Van Allen Belt have been correlated using recent data obtained from the radiation research satellite, OV3-4. Six tissue equivalent ionization chambers, constructed of a material which simulates the muscle tissue response to ionizing radiation, measured the dose rate behind various types and thicknesses of material. The specific shields used for several of the chambers were 0.192 g/cm2 aluminum, 0.797 g/cm2 Lucite and 4.485 g/cm2 brass. The proton and electron spectra were determined with an omnidirectional spectrometer using solid state detectors. The spectral measurements discussed here include geomagnetically trapped protons with energies in the range of 15 to 200 MeV. The proton spectra and dose rates are presented as profiles in terms of the McIlwain parameters of L (1.5, 2.0 and 2.5 earth radii) and the magnetic field B (0.050 to 0.250 gauss). The excellent agreement between the measured dose rate and the theoretically predicted dose rate based on the measured spectra provides justification for the radiation transport techniques now being employed to predict the doses to be encountered during future manned space missions. It was found, however, that a more adequate description of the proton fluxes for energies greater than 50 MeV will be necessary to predict dose rate accurately behind shields of 2.5 g/cm2 thickness or greater.

Cosmic Radiation↗
PubMedDate not supplied

A custom template and definitive prosthesis allowing immediate implant loading in the maxilla: a clinical report.

PURPOSE: The purpose of the present investigation was to examine to what extent precision data from 3-dimensional planning software for oral implants can be transferred to the operative field by means of a drilling template, containing high-precision drilling sleeves, fitted on the jawbone. It was investigated whether this procedure would allow advance preparation of a fixed definitive prosthesis that could be placed at the completion of surgery. MATERIALS AND METHODS: This procedure was experimentally carried out in 2 cadavers and later in 8 consecutive human patients. RESULTS: The results indicated a nearly perfect match between the positions and axes of the placed implants and those planned. DISCUSSION: This procedure permitted the placement of a definitive fixed prosthesis with limited freedom of space between the abutments and the metallic cylinders incorporated into the prosthesis. CONCLUSION: These encouraging results of the Leuven information technology-based oral rehabilitation by means of implants (LITORIM) are presently being further investigated at the clinical level.

Cadaver↗