Colonne vertébrale | EPFL Graph Search

La colonne vertébrale (aussi échine ou rachis) est un empilement d'os articulés appelés vertèbres. Elle est le support du dos des vertébrés, dont elle constitue une synapomorphie. C'est sur la colonne vertébrale que sont fixées, quand elles existent, les côtes et les ceintures scapulaire et pelvienne. Elle a une triple fonction : statique (maintien de la position érigée contre la pesanteur grâce aux corps vertébraux qui supportent les pressions exercées par le poids du corps et les transmettent aux membres), dynamique (permettant la gamme étendue des mouvements de la tête et du tronc déterminés par l'orientation des surfaces de glissement des processus articulaires), et protectrice (protection de la moelle spinale siégeant à l'intérieur du canal rachidien formé par les foramens des vertèbres). Chez l'être humain, elle supporte la tête et transmet le poids du corps jusqu'au bassin qui le transmet aux articulations des hanches. Elle est composée, comme chez d'autres mammifères, de vin

Structural architecture of the Neuronal-Glial-Vascular system

Eleftherios Zisis

Brain functionality relies on the neuronal-glial-vascular (NGV) ensemble for energy support. However, the details of the complex biological mechanisms involved in these processes and the microscopic interactions between these three components are not yet fully understood. Astrocytes, an essential component of the NGV ensemble, extend ramified processes to the vasculature and to neuronal synapses to provide neuronal energy support, homeostatic control, and multi-directional signaling with the vasculature, neurons, and neighboring astrocytes. As key links between the components of the NGV circuitry, the astrocytes are essential for drug delivery in the brain and are involved in the progression of neurodegenerative diseases. Therefore, comprehensive models of the neuronal-glial-vascular (NGV) ensemble are essential for understanding the role of astrocytes in the formation and function of the complex networks within the brain and its pathological conditions. A complete computational model of this ensemble has not yet been developed. This thesis presents the first model of a data-driven digital reconstruction of the neuronal-glial-vascular (NGV) ensemble at a micrometer anatomical resolution. Combining the sparse literature data and the few available detailed biological reconstructions, I have computationally generated the structural architecture of a neocortical NGV circuit that forms a functional column of the juvenile rat neocortex and consists of neurons, protoplasmic astrocytes, and the microvasculature, including their pairwise connectivities. This data-driven approach allows for incremental refinement as more experimental data become available, new biophysical models get published, and new questions arise. The NGV circuit is validated against a plethora of literature sources to ensure its biological fidelity: it successfully reproduces the spatial organization of the astrocytes, their morphological characteristics as well as their volume occupancy, and the overlap with their neighbors. The power of the computational model of NGV lies in its ability to serve as a framework for addressing long-standing questions that cannot be experimentally investigated due to the complexity of the microscopic systems and the limitations of current techniques to observe all components simultaneously. In this thesis, I have performed experiments to investigate why astrocytes acquire their particular shapes, the organizational principles of NGV that lead to the observed biological network architectures, and the effect of astrocytic density on endfoot organization. The circuit's structural analysis showed that astrocytes optimize their positions and spacing from each other to provide the vasculature with a uniform coverage for trophic support and signaling. By increasing the density of astrocytes in NGV circuits, I discovered a limit in astrocyte's ability to make perivascular projections because of the vascular spatial occupancy, which constrains the extent of astrocyte morphology. Thus, their role in linking vasculature to neurons constrains their organization via the proportional relationship of density and microdomain shrinkage due to contact spacing. By addressing these questions, I demonstrated how this model can serve as an exploratory tool that provides a window into the complexity of the NGV architecture.

EPFL2021

Comparison of Seismic Design Requirements for Steel Moment Resisting Frames with Emphasis on Stability of Columns in North America, New Zealand, and Europe

Ali Imanpour, Dimitrios Lignos

The seismic design provisions and stability requirements for steel columns used at the first storey of MRFs as specified is Canadian steel design standard (CSA S16), U.S. design provisions for steel buildings (AISC 341 and AISC 360), the New Zealand steel structures standard (NZS 3404), and Eurocodes 3 and 8 (EC3 and EC8) are reviewed. The code provisions are applied to a deep, slender steel I-shaped column to identify possible failure modes. A finite element analysis of the column is performed under cyclic inelastic lateral drift history to validate code predictions. The column was found to fail by out-of-plane instability, after local buckling has developed in the base plastic hinge. This failure mode was not expected from the axial-bending interaction equations available in the design standards except the equation of Eurocode 3. Limits for out-of-plane slenderness in Canadian and European provisions indicate the observed failure mode.

2016

Spinal Subarachnoid Space Pressure Measurements in an In Vitro Spinal Stenosis Model: Implications on Syringomyelia Theories

Bryn Andrew Martin

Full explanation for the pathogenesis of syringomyelia (SM), a neuropathology characterized by the formation of a cystic cavity (syrinx) in the spinal cord (SC), has not yet been provided. It has been hypothesized that abnormal cerebrospinal fluid (CSF) pressure, caused by subarachnoid space (SAS) flow blockage (stenosis), is an underlying cause of syrinx formation and subsequent pain in the patient. However, paucity in detailed in vivo pressure data has made theoretical explanations for the syrinx difficult to reconcile. In order to understand the complex pressure environment, four simplified in vitro models were constructed to have anatomical similarities with post-traumatic SM and Chiari malformation related SM. Experimental geometry and properties were based on in vivo data and incorporated pertinent elements such as a realistic CSF flow waveform, spinal stenosis, syrinx, flexible SC, and flexible spinal column. The presence of a spinal stenosis in the SAS caused peak-to-peak cerebrospinal fluid CSF pressure fluctuations to increase rostral to the stenosis. Pressure with both stenosis and syrinx present was complex. Overall, the interaction of the syrinx and stenosis resulted in a diastolic valve mechanism and rostral tensioning of the SC. In all experiments, the blockage was shown to increase and dissociate SAS pressure, while the axial pressure distribution in the syrinx remained uniform. These results highlight the importance of the properties of the SC and spinal SAS, such as compliance and permeability, and provide data for comparison with computational models. Further research examining the influence of stenosis size and location, and the importance of tissue properties, is warranted. [DOI:10.1115/1.4000089]

2010

Structural architecture of the Neuronal-Glial-Vascular system

Eleftherios Zisis

EPFL2021