42 research outputs found
Shapeshifting for memory: Biochemical and electrical signaling in dendritic spines
No full textOne of the biggest remaining mysteries of science is inside our heads: how does nature wire up a high-performance computer without having a detailed blueprint specifying the location and strength of every connection? It is assumed that local connectivity in our cortex is at first random, and during development undergoes refinement until only the ‘right' connections are left over. But how can the brain tell ‘right' from ‘wrong' connections? The majority of excitatory connections are formed on dendritic spines, tiny excrescences that cover almost the entire dendritic surface of most neurons. Since their discovery by Ramón y Cajal in 1896, neuroscientists have been fascinated by these structures, which ultimately determine which neurons in the brain become connected and form functional networks. Here we review the many important functions of spines and explain why electrical and biochemical processes in these tiny structures are thought to be crucial for the plasticity of the brai
Shapeshifting for memory
No full textAbstract
One of the biggest remaining mysteries of science is inside our heads: how does nature wire up a high-performance computer without having a detailed blueprint specifying the location and strength of every connection? It is assumed that local connectivity in our cortex is at first random, and during development undergoes refinement until only the ‘right’ connections are left over. But how can the brain tell ‘right’ from ‘wrong’ connections? The majority of excitatory connections are formed on dendritic spines, tiny excrescences that cover almost the entire dendritic surface of most neurons. Since their discovery by Ramón y Cajal in 1896, neuroscientists have been fascinated by these structures, which ultimately determine which neurons in the brain become connected and form functional networks. Here we review the many important functions of spines and explain why electrical and biochemical processes in these tiny structures are thought to be crucial for the plasticity of the brain.</jats:p
Continuous-time System Identification: A Bilinear Optimization Approach
No full textIn the noiseless case, the identification of a grey-box model can be posed as a feasibility problem, i.e. determining if existent - and if so - finding a parameter vector such that the parametric model equals the actual model (or its associated input-output data). Being that in this thesis we are interested in continuous-time grey-box identification, we shall be dealing with models that allow for forming a direct relationship with physical meaningful quantities. Such models include the state space representation and the matrix differential equation. In general, identifying such grey-box models turns out to be a non-convex problem. In this thesis, we initially review a framework which allows us to solve feasibility problems which have bilinear constraints. It turns out that most of the aforementioned non-convexities can be captured into a single bilinear matrix equation. However, the resulting feasibility problem, including the bilinear matrix equations, makes the overall search for the actual parameter vector NP-hard. In order to come up with numerical tractable algorithms, we use a heuristic known as Sequential Convex Relaxation to relax the bilinear equality constraints. This iterative scheme is flexible enough to allow for additional (in)equality constraints, possibly resembling any other physical constraints. We explore two different approaches to identify both the state space model and the matrix differential equation; one, by directly identifying the model from the given frequency response function; two, by first identifying a black-box model before performing a small scale optimization problem, transforming the black-box model such that it fits the grey-box parameterization. In addition, we present a novel method which uses the Power Spectral Density to estimate a 2nd order model. All methods are numerically validated.Mechanical Engineering | Systems and Contro
Cellular and nuclear morphology…and calcium signaling: revealing the interplay between structure and function
No full textPoster presentation: Calcium plays a pivotal role in relaying electrical signals of the cell to subcellular compartments, such as the nucleus. Since this one ion type is used by the cell for many processes a neuron needs to establish finely tuned calcium pathways in order to be able to differentiate multiple tasks, [1-3].
While it is known that neurons can actively change their shape upon neuronal activity, [4-7], we here present novel findings of activity-regulated nuclear morphology, [8,9]. With the help of an experimental and computational modeling approach, we show that hippocampal neurons can change the previously spherical shape of their nuclei to complex and infolded morphologies. This morphology regulation is demonstrated to be regulated by NMDA-receptor gated calcium, while synaptic and extra-synaptic NMDA-receptors elicit opposing effects on nuclear morphology, [8].
The structural alterations of the cell nucleus have significant effects on nuclear calcium dynamics. Compartmentalization of the nucleus, due to membrane infoldings, changes calcium frequencies, amplitudes and spatial distributions, [8,10]. Since these parameters have been shown to control downstream events towards gene transcription, [11,12], the results elucidate the cellular control of nuclear function with the help of morphology modulation. With respect to processes downstream of calcium, we show that histone H3 phosphorylation is closely linked to nuclear morphology. Investigating the nuclear morphologies of hippocampal neurons, two major classes were identified [9,10]. One class contains non-infolded nuclei that have the function of calcium signal integrators, while the other class contains highly infolded nuclei, which function as frequency detectors of nuclear calcium, [10].
Extending this interdisciplinary approach of investigating structure/function relationships in neurons, the effects of cellular morphology – as well as the morphology of the endoplasmic reticulum and other organelles – on neuronal calcium signals is currently being investigated. This endeavor makes use of highly detailed, three-dimensional models of neuronal calcium dynamics, including the three-dimensional morphology of the cell and its organelles
An upper limit on gas production from 3200 Phaethon
No full textThis article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit
Imaging of molecular surface dynamics in brain slices using single-particle tracking
No full textContains fulltext :
135922.pdf (Publisher’s version ) (Open Access)Organization of signalling molecules in biological membranes is crucial for cellular communication. Many receptors, ion channels and cell adhesion molecules are associated with proteins important for their trafficking, surface localization or function. These complexes are embedded in a lipid environment of varying composition. Binding affinities and stoichiometry of such complexes were so far experimentally accessible only in isolated systems or monolayers of cell culture. Visualization of molecular dynamics within signalling complexes and their correlation to specialized membrane compartments demand high temporal and spatial resolution and has been difficult to demonstrate in complex tissue like brain slices. Here we demonstrate the feasibility of single-particle tracking (SPT) in organotypic brain slices to measure molecular dynamics of lipids and transmembrane proteins in correlation to synaptic membrane compartments. This method will provide important information about the dynamics and organization of surface molecules in the complex environment of neuronal networks within brain slices
Water regimes and marsh distribution. In: McComb, A.J., Kobryn, H.T. and Latchford, J.A. (eds) Samphire marshes of the Peel-Harvey estuarine system Western Australia.
No full textTide has long been recognised as the most influential factor determining plant zonation and the development of saltmarsh communities, and it is the tide that largely determines the structure and function of saltmarshes (Clarke & Hannon, 1969).
The zonation of species with increasing distance from the water's edge and increasing elevation is initially determined by the frequency of tidal flooding and the tolerance of various species to this (Huiskes, 1990). Tidal range usually sets the upper and lower limits of the marsh. The lower limits are set by depth and duration of flooding, and the consequent mechanical effect of the waves, sediment availability and rate of erosion. The upper limits are influenced mainly by soil water salinity and nutrient availability, both of which are linked to tidal flooding frequency (Mitsch & Gosselink, 1993), tidal water being the main source of soil salt and the major mechanism for nutrient transport (Clarke & Hannon, 1971)
The significance of saltmarshes. In: McComb, A.J., Kobryn, H.T. and Latchford, J.A. (eds) Samphire marshes of the Peel-Harvey estuarine system Western Australia.
No full textSaltmarshes are complex ecosystems. Numerous studies have been undertaken on them in different parts of the world, mostly in the northern hemisphere. A few previous studies have been made of the marshes of the Peel-Harvey System (Rose & McComb, 1980; Backshall & Bridgewater, 1981; McComb & Lukatelich, 1986) but increased pressure for development, and the need for an understanding the possible effects of the then proposed Dawesville Channel highlighted the lack of information about saltmarshes in the area. This report endeavours to addresses this lack of information by presenting recent research into the extent, composition and functioning of the Peel-Harvey saltmarshes
